Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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INDEX
S.No PAPER TITLE AUTHOR’S NAME PAGE No.
KEY NOTE LECTURE
1 ADVANCED CEMENT BASED COMPOSITES –A
NEW INNOVATION IN MATERIALS
TECHNOLOGY
Dr.M. NEELAMEGAM 3
2 RECENT TRENDS IN STEEL STRUCTURES Dr. L.S.JAYAGOPAL 13
3 GOOD RCC CONSTRUCTION PRACTICE TO
PREVENT CORROSION OF STEEL
Dr.K.JAGADEESAN 28
4 SMART MATERIALS AND SMART
STRUCTURES
Dr.PERUMAL PILLAI
50
5 SEISMIC RESPONSE OF SIFCON STRUCTURAL
ELEMENTS
Dr.G.S.THIRUGNANAM
70
PAPERS PRESENTED
6 STUDY ON FIBRE REINFORCED
CEMENTITIOUS COMPOSITES
Dr.A.JAGANNATHAN
87
7 PERFORMANCE OF CONCRETE ONE WAY
SLABS REINFORCED WITH NON METALLIC
REINFORCEMENTS UNDER CONSTANT AND
VARIABLE REPEATED FATIGUE LOADING
Dr.R.SIVAGAMASUNDARI
Dr.G.KUMARAN 100
8 DUCTILE BEHAVIOR REINFORCED
CONCRETE BEAM – COLUMN JOINTS
SUBJECTED TO CYCLIC LOADING
Prof.A.MURUGESAN
Dr.G.S.THIRUGNANAM 118
9 CORROSION MONITORING OF ELECTRIC
TRANSMISSION LINE TOWER FOUNDATIONS
AND EVALUATION METHODS
- A CASE STUDY
Mr.S.CHRISTIAN JOHNSON
Dr.G.S.THIRUGNANAM 136
10 PROPERTIES OF BRICKS WITH PARTIAL
REPLACEMENT OF BRICK EARTH BY STEEL SLAG
Prof.P.S.KOTHAI
150
11 STUDY ON FLY ASH BASED GEO-POLYMER
CONCRETE.
Prof..C.CHELLA GIFTA 163
12 DESIGN OF COLD-FORMED STEEL PLAIN
CHANNELS
Prof.S. MANJULADEVI
176
13 EFFECT OF THICKNESS OF SHEET IN
BEHAVIOUR OF HOLLOW COLDFORMED
STEEL CONCRETE COMPOSITE COLUMN
USING SELF COMPACTING CONCRETE
N.K.Amudhavalli,
N.Balasubramaniam,
Dr.R.Thenmozhi
Dr.M.K.Saseetharan 186
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14 EXPERIMENTAL INVESTIGATION ON
BEHAVIOUR OF REINFORCED HIGH
PERFORMANCE CONCRETE BEAMS
Prof.P.MUTHUPRIYA,
Dr.B.G.VISHNURAM
Dr.K.SUBRAMANIAN 196
15 NEW TECHNIQUES IN ASEISMIC DESIGN Prof.A.K.KALILUTHIN
Prof.S.RAMANATHAN 209
16 EXPERIMENTAL STUDY OF RETROFITTING
WITH GFRP ON RC ELEMENT UNDER
FLEXURE
Prof.N.R.CHITRA,
Miss.R.ANITHA DEEL
Dr.R.MURUGESAN
219
17 STRENGTHENING ON RC ELEMENTS WITH
GFRP UNDER FLEXURE
Prof.P.SARAVANAKUMAR,
Prof.G.M.GOWTHAMKUMA
R, Miss.T.SRIVIDYA
Dr.R.MURUGESAN
229
18 EXPERIMENTAL STUDIES ON VIABILITY OF
USING GEOSYNTHETICS AS FIBERS IN
CONCRETE
R.Gobinath, K.Rajeshkumar
237
19 EXPERIMENTAL STUDIES ON REDUCING
THICKNESS OF FLEXIBLE PAVEMENTS BY
USING WOVEN AND NON-WOVEN
GEOSYNTHETICS IN SUBSURFACE
R.Gobinath, K.Rajeshkumar
253
20 USE OF SAWDUST ASH IN CONCRETE AS PART
REPLACEMENT OF SAND
M.Mageswari, Dr.B.Vidivelli
266
21 AN EXPERIMENTAL STUDY ON HIGH
PERFORMANCE CONCRETE WITH SILICA
FUME AND FLY ASH AS PARTIAL
REPLACEMENT OF CEMENT
K.R.Muthuswamy,
Dr.G.S.Thirugnanam
273
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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ADVANCED CEMENT BASED COMPOSITES –A NEW INNOVATION IN
MATERIALS TECHNOLOGY
M. Neelamegam*
* Director Grade Scientist and Head Construction Engineering Laboratory, Structural
Engineering Research Centre, CSIR Campus, Chennai – 600113
ABSTRACT
Advanced cementitious composites (ACC‘s) , such as, ultra high performance fiber reinforced
concrete (UHPFRC) and reactive powder concrete (RPC) are a new generation of engineered
cementitious composites employing optimum combination of mineral admixtures, hard, fine
fillers, fibers and modified processing and curing techniques. ACCs are characterized by greater
homogeneity, optimum packing of components, dense and compact microstructure and enhanced
aggregate interface bond. The compressive strength ranges from 150 to more than 200 MPa and
the flexural strength can be as high as 40 MPa or more depending on the fiber content. At the
Structural Engineering Research Centre, Chennai, R & D work is currently under progress to
develop advanced cementitious composites like reactive powder concrete and investigate the
performance of some typical products. Such products would be of benefit to the pre-cast industry
and help in the production of better quality products with enhanced performance. The paper
presents an outline of the development work on RPC undertaken by SERC, Chennai and the
salient findings from the work.
1.0 INTRODUCTION
Advanced Cementitious composites are a new generation of cement based materials with a high
compressive strength of more than 200 MPa and that exhibit exceptional durability and ductility
characteristics and their development marks a quantum leap in concrete technology. This high
performance material offers a variety of interesting applications. It allows the construction of
sustainable and economic buildings with an extraordinary slim design. Its high strength and
ductility makes it the ultimate building material e.g. for bridge decks, storage halls, thin-wall shell
structures and highly loaded columns. Besides its improved strength properties, its outstanding
resistance against all kinds of corrosion is an additional milestone on the way towards no-
maintenance constructions. UHPC has very special properties that are remarkably different to the
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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properties of normal and high performance concrete. For complete utilization of UHPCs superior
properties, special knowledge is required for production, construction and design.
Development of ACCs was made possible due to the introduction of new reinforcement system,
densification of microstructure by optimum particle packing and synergetic combination of highly
reactive components, strong fiber-matrix-aggregate and special thermo-mechanical processing.
Several types of ACCs have been developed over the last couple of decades. They include:
DSP (Densified Small particle system)
MDF (Macro-defect free) cements
RPC (Reactive powder concrete)
ECC (Engineered cementitious composites)
SIFCON (Slurry infiltrated fiber reinforced concrete)
SIC (Special industrial concrete)
Multi-scale FRC
DSP is produced with high superplasticizer and silica fume (SF) by incorporating ultra-hard
aggregate (calcinated bauxite or granite). The compressive strength of this material can vary
between 150 and 400 MPa.
Macro-defect-free (MDF) cement is polymer modified cement mortar pastes produced by special
processing techniques to eliminate the flaws and defects. These pastes have very high tensile
strength (above 150 MPa), particularly when mixed with aluminous cement.
The other types of ACCs combine the principles of DSP and MDF cements to achieve the desired
improvements.
Compact Reinforced Composites (CRC) use metal fibers, 6 mm long and 0.15 mm in diameter,
and fiber volume fractions in the range of 5 to 10 %. The increase of strength is greater than the
increase in ductility.
Reactive Powder Concrete [1-13] is a type of UHPFRC containing a maximum of 2.5% metal
fibers which are 13 mm long and 0.16 mm in diameter.
Slurry-Infiltrated-fibered concrete (SIFCON) consists in placing the fibers in a formwork and
then infiltrating a high w/c ratio mortar slurry to coat the fibers. Compressive and tensile strengths
up to 120 MPa and 40 MPa, respectively have been obtained.
Engineered Cementitious Composite (ECC): is obtained by optimizing the interactions between
fiber, matrix and its interface. By tailoring the micromechanical characteristics, a small volume
fraction of 2% is able to provide the large ductility. ECCs contain synthetic fibers (length 20mm),
dia <0.05mm) with a low density (< 1.5) and high elastic modulus (> 40 GPa), and possess very
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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high specific surface. The compressive strength is generally 70 MPa and the tensile strain capacity
is more than 5-15%
Multi-scale Fiber-Reinforced Concrete (MSFRC): They are produced by a combination of
short and long fibers to increase the tensile strength, the bearing capacity, and the ductility.
2.0 Basic Principles for the Development of UHPFRC
In essence, the following principles underlie the development of UHPFRC
1. Homogenization: -complete or partial elimination of the coarse aggregates for enhancement of
homogeneity.
2. Pozzolanic activation: Utilization of the pozzolanic properties of silica fume and quartz.
3. Optimum packing: Optimization of the granular mixture for the enhancement of compacted
packing density.
4. Thermo-mechanical processing
a) Optimal usage of SP to achieve proper dispersion and workability with very low w/p
(water-powder ratio).
b) Application of pressure (before and during setting) to improve compaction.
c) Post set heat treatment for the enhancement of the microstructure.
5. Micro-reinforcing: addition of small sized steel fibers to improve strength and ductility.
3.0 INVESTIGATIONS CARRIED OUT AT SERC ON RPC
1. Preliminary Investigations
Preliminary Investigations were carried out to identify the various types of materials to be used for
the production of reactive powder concrete. Initially, the basic properties of cements namely
standard consistency, initial and final setting time and compressive strength, etc. were studied.
Similarly, the specific gravity and the particle size of the various materials like cement, silica
fume, quartz, standard sand, etc., were studied which may be required for detailed investigations.
2. Selection of Materials
The selection of materials depends on various the physical and chemical properties, such as,
particle size, specific gravity, glass content, purity, etc. Also, the compatibility and performance in
the presence of other materials need to be established which may help in shortlisting of the
materials when two or more types are available.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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Selection Criteria:
Cement: It is necessary that the cement for reactive powder concrete should possess higher tri-
calcium silicate and lower tri-calcium aluminate contents and should have higher fineness.
However, due to the non-availability studies are carried out with the available OPC.
Silica fume: Higher the purity and fineness better is the reactivity.
Aggregate: It is preferable to have non-flaky, equi-angular aggregates the maximum size of
aggregates is restricted to 600μm.
Silica Sand: Standard Grade silica sand (I, II and III) is used for the study. If, available it is
preferable to use quartz sand.
Quartz Powder: It is recommended to use quartz powder between 5 -20μm.
Steel fiber: Micro-steel fibers of high tensile strengths and 6 to 13 mm length and less than 0.15
mm diameter are best suited.
3. Standard Mix Proportions for Reactive Powder Concrete
Sixteen trial mixes were carried out based on literature survey (Tables 1 and 2) and considering
the selection criteria. The trial mix which gave the best performances both in terms of strength and
workability was finalized The standard mix proportion and quantity of materials per m3
of reactive
powder concrete is shown in Table 3.
4. Preparation of the specimen
The required quantity of RPC mixes was prepared by intensive mixing using a planetary mixer to
produce a flowable consistency. The mix was placed and compacted in steel moulds.
5. Curing Cycle
Based on detailed investigations, a curing protocol involving combination of normal water curing,
hot water curing and high temperature curing was arrived at. Fig. 1 shows the curing regime
adopted. Compressive strength of about 188 MPa was obtained after incorporating 2% micro-steel
fibers. The effect of heat treatment on compressive strength of RPC is shown in Fig. 2.
6. Adoption of pre-compression techniques
To achieve further enhancement in strength, the pre-set compression technique was used. A
pressure of 60 MPa was employed. By this process, compressive strength of 215MPa was
achieved.
7. Check for consistency
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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As seen from Fig. 3, an average compressive strength of 192 MPa is produced having a standard
deviation of 7.25 MPa and co-efficient of variation less than 10%.
8. Investigation on Mechanical properties
It is found that the compressive strength was 215 MPa and 196 MPa for RPC specimens with and
without pre-compression, respectively. The split tensile, flexure and impact strength were found to
be 18MPa, 27 MPa and >7000 Joules, respectively.
9. Structural sections
Structural section like rectangular, I and channel sections of appropriate dimensions were cast
using the standard RPC mix and adopting standardized curing regime. The size of the rectangular
section is 75 x 75 x 350 mm. The load-deformation plot for the rectangular section is shown in
Fig. 4.
10. Durability studies of Reactive Powder Concrete
Various durability tests such as water absorption and sorptivity, water and chloride permeability,
resistance to chemical attacks such as acid, salt, sulphate, carbonation etc., electrical resistivity
have been initiated and are currently in progress.
CONCLUSION
1. It is possible to produce ultra high performance concretes with conventionally available
materials and achieve a compressive strength of the order of 215 about MPa.
2. The selection of material plays a key role in producing RPC.
3. The mix proportion and curing regime are the main factors in deciding the target compressive
strength. The target compressive strength is less without heat treatment. Heat treatment
accelerates the cement hydration and pozzolanic action at the initial stage and makes the
quartz reactive at the later stages of initial heat curing regime.
4. The process of pre-compression helps in removing the water present in excess that is required
for compaction. The compaction pressure can be increased to 60 MPa for better performance.
This results in reduced porosity and overcomes chemical shrinkage.
5. The desired mechanical properties are produced with the application of the basic principles of
RPC viz., homogenization, optimum packing, pozzolanic activation, micro-reinforcing and
thermo-mechanical processing.
6. Using reactive powder concrete, it is possible to produce thin structural sections like I,
Channel, etc., which can give high flexural strength and ductility.
ACKNOWLEDGEMENT
This invited paper is published with the kind permission of the Director, SERC, Chennai. The
authors sincerely thank their colleagues and technical staff in the concrete composites laboratory
of SERC for their help and encouragement.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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REFERENCES
1. Bonneau Oliver, Lachemi L., Dallaire E., Dugat J. and Aitcin, P.C., [1997] ―Mechanical
Properties and Durability of two Industrial Reactive Powder Concretes, ACI Materials
Journal, July-Aug 1997, pp 286-290.
2. Dili, A.S. and Manu Santhanam, [2004] ―Investigations on Reactive Powder Concrete: A
Developing Ultra High-Strength Technology‖, The Indian Concrete Journal, pp. 33-38
3. Dugat, J., Roux, N. and Benier, G., [1996] ―Mechanical Properties of Reactive Powder
Concretes‖, Materials and Structures, RILEM, Vol.29, May 1996, pp.233-240.
4. Enab Shateen and Nigel G. Shrive (2006), ―Optimization of Mechanical properties and
Durability of Reactive powder Concrete,‖ ACI material journal, Title No. 103 – M49, pp.
444-451.
5. Feylessoufi, A., Villeras, L, Michot, P, De Donato, Cases, J, M, and Richard, P., [1996]
―Water Environment and nano-structural Network in Reactive Powder Concretes‖, Cement
and Concrete Composites, 18, 23-29.
6. Jianxin Ma, Marko Orgass [2004], ―Comparative Investigations on Ultra-High
Performance With and Without Coarse Aggregates‖, Institut fur Massivbau und
Baustofftechnologie, Universitat Leipzig.
7. Lee, N.P. and Chisholm, D.H., [2005] ―Reactive Powder Concrete‖, Study Report, Branz,
New Zealand.
8. Matte, V. and Moranville, M., [1999] ―Durability of Reactive Powder Composites:
Influence of Silica Fume on the Leaching Properties of Very Low Water/Binder Pastes‖,
Cement and Concrete Composites, 1999, 21, pp.1-9.
9. Morin, V, Cohen Tenoudji, F., Feylessoufi, A., and Richard, P., [2002], ―Evolution of
Capillary Network in a Reactive Powder Concrete pp, 1907-1914.
10. Richard, P. and Cheyrezy, M., [1995] ―Composition of Reactive Powder Concretes‖,
Cement and Concrete Research, Vol.25, No.7, pp 1501-1511.
11. Roux, N., Andrade, C. and Sanjuan, M.A., [1996] ―Experimental Study of Durability of
Reactive Powder Concretes‖, Journal of Materials in Civil Engineering, pp.1-6.
12. Staquet S, and Espion B, [2000], ―Influence of Cement and Silica Fume Type on
Compressive Strength of Reactive Powder Concrete‖, 6th International Symposium on
HPC, University of Brussels, Belgium, pp 1 to 14.
13. Yin-Wen Chan and Shu-Hsien Chu, [2004] ―Effect of Silica Fume on Steel Fiber Bond
Characteristics in Reactive Powder Concrete‖, Cement and Concrete Research, 34, pp.
1167-1172.
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Table 1 List of Major Investigations Reported in Reactive
Powder Concrete
Names of
Researchers Year Country
Target CS
(MPa)
Richard and Cheyrezy 1995 Canada,
France
170, 288,
230, 275
Feylessoufi et al 1996 France 230
Dugat et al 1996 France 203
Roux et al 1996 Italy 170
Oliver Bonneau et al 1997 Canada 217, 197
Bouygues 1997 France --
Matte 1999 France 216
Staquet 2000 France --
Morin et al 2002 France --
Yin-Wen Chan et al 2003 Taiwan --
Dilli et al 2004 India 130, 198
Orgass et al 2004 Europe 188
Jianxin Ma et al 2004 China 190
Lee and Chisholm 2005 New Zealand 211, 230
Ehab Shaheen et al 2006 USA --
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Table 2 Typical Mix Proportions Used for RPC
(Richard and Cheyrezy, 1995)
Materials Richard and Cheyrezy
Target Strength (MPa) 170 288 230 275
Port land Cement 1.00 1.00 1.00 1.00
Silica fume 0.25 0.23 0.25 0.23
Precipitated silica 0.01 -- -- --
Sand 1.10 1.10 1.10 1.10
Crushed quartz -- 0.39 -- 0.39
Super-plasticizer 0.016 0.019 0.016 0.019
Fibers -- -- 0.175 0.175
Water 0.15 0.17 0.17 0.19
Pre-set Pressure (MPa) -- -- -- --
Heat Treatment Temp. 20°C 90° C 20° C 90° C
Table 3 Standard Mix Proportions for Reactive Powder Concrete Developed at the
Structural Engineering Research Centre, Chennai
Mix ID Mix Proportions
SF C Q FA w/c SP STF
Finalized
Mix
for RPC
0.25 1 0.4 1.1 0.17 3 0.2 (2%
by vol.)
Quantity of Materials / m3 of concrete
SF C Q Sand w/c SP STF
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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kg kg kg kg l l kg
198 792 317 871 135 30 160
SF – Silica Fume, C – Cement, Q – Quartz, FA – Fine Aggregate, W – Water, SP – Super
Plasticizer, STF-Micro-Steel Fibers
0
50
100
150
200
250
0 1 2 3 4 5 6 7 8 9 10
Curing Period (days)
Tem
per
atu
re (
deg
. C
)
Fig. 1 Curing Cycle for RPC
Fig. 2 Effect of Heat treatment on Compressive Strength of RPC
0
20
40
60
80
100
120
140
160
180
200
0 5 10 15 20 25 30
Period of Curing (days)
Co
mp
ress
ive
Str
eng
th
(MP
a)
NWC
HWC-60 C
HWC-90 C
Comb. (AC)
Comb. (HAC)
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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]
Fig. 3 Consistency Chart for RPC
(Avg. = 190.86 MPa, SD = 11.44 MPa, COV = 5.99 MPa)
Fig. 4 Load-deformation Plot for Reactive Powder Concrete with Varying Fiber Contents
75
100
125
150
175
200
225
250
0 5 10 15 20 25 30 35
Number of Specimens
Co
mp
ress
ive S
tren
gth
(M
Pa
)
Compressive Strength of Individual Sample
Average Compressive Strength
0
10
20
30
40
0 1 2 3 4 5 6
Deformation (mm)
Lo
ad
(K
N)
RPC-1%
RPC-2%
RPC-3%
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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RECENT TRENDS IN STEEL STRUCTURES
Dr. L.S.Jayagopal*
* Managing Director, Mithran Structures (P) Limited
Coimbatore
1. Introduction
In the field of steel structures developments in materials, sections connections design and
constructions are happening continuously. It is not possible to list down and detail all these
developments. Few developments which are pertinent to present adoption are briefly provided in
this paper. They are
1. High strength steel and their use
2. Wide flanged I section, Hollow section
3. Open web trusses, deck sheet and concrete composite sections
4. Lattice beams and columns
5. Connections with high strength friction grip bolts
6. Coated metal sheets – types and uses
7. Corrugated web sections
Still research is on in some of the above areas. But they have already been adopted
successfully in the field. In many situations practice precedes research.
2. High Strength Steel
The column steel section available in India is carbon steel (IS 2062) with carbon and
manganese as alloying material. The standard structural steel designated as Fe 410 has ultimate
tensile strength 410 mPa and yield strength of 250 mPa. Micro alloyed medium and and high
strength steel designated Fe 440, Fe 540, and Fe 590 have yield strengths 350 mPa 410 mPa and
450 mPa respectively.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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Compared to Indian steel, steel with enhanced strengths are available as imported material
.. These steels are alloyed steel of vanadium, niobium and titanium with low carbon and
manganese contents. One variety of Swedish steel available in Indian market Named Dome 640
mPa has an yield strength of 550 mPa. Steel with yield strengths up to 740 mPa are also available.
These high strength steels possess the characteristics of formability, weldability, and impact
toughness. They can be cut and welded with laser and they are suitable for hot dip galvanizing.
3. Sections
3.1 Wide Flanged Sections
ISMB, ISMC and equal angles are only sections that are processed in India on account of
rolling wheels available. ISMB members are traditionally used as column members. ISMB
sections have low radius of gyration in the weaker axis. Hence they are not economical for axially
loaded columns and laterally unsupported beams. Parallel flange sections are hot rolled steel
sections, with parallel flanges. This flange design results in higher section modulus. Parallel flange
sections are more efficient than the conventional tapered flange sections in terms of strength,
workability and economy. Connections are far simpler in parallel flange sections.. The use of these
sections was not very common in India until recently, because of non-availability of the same in
medium and large sizes. Such sections are now being produced in India and it is expected that the
use of these efficient sections will increase. The code IS 12778: 2004 covers the nominal
dimensions; mass and sectional properties of hot rolled parallel flange beams, columns and bearing
piles. Some sections presently rolled are listed below.
3.2 Hollow Steel Sections
Tubular members extensively used in structures are efficient in resisting and torsion. It has
been practiced to produce welded connection with out gusset plates. The flow drill and hollow bolt
provide choice of methods to produce bolted joints with hollow tubes. Hollow Structural Sections,
especially rectangular sections, are commonly used in welded steel frames where members
experience loading in multiple directions. Square and circular hollow sections have very efficient
shapes for this multiple-axis loading as they have uniform geometry and thus uniform strength
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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characteristics along two or more cross-sectional axes; this makes them good choices for columns.
They also have excellent resistance to torsion
HSS can also be used as beams, although I- beam shapes are in many cases a more
efficient structural shape for this application. However, the HSS has superior resistance to lateral
torsional buckling.
Square HSS is made the same way as pipe. During the manufacturing process flat steel plate is
gradually changed in shape to become round where the edges are presented ready to weld. The
edges are then welded together to form the mother tube. During the manufacturing process the
mother tube goes through a series of shaping stands and cold forms the round HSS (mother tube)
into the final round, square, or rectangular shape They are classified hot finished welded (HFW),
Hot finished seam less (HFS), Electric resistance welded (ERN) cold drawn electric resistance
welded (CEW) ect., They are available from 15mm OD to 200mm OD with list, Medium and
heavy grades with thickness from 1.6mm to 6mm square hollow tubes (SHS) and rectangular
hollow sections (RHS) are available, as per IS4923 standards. They have an yield strength of 250
mPa and ultimate strength of 410 mPa. They are made with cold bending of sheets thickness
1.6mm to 10mm and seam welding with high frequency induction welding techniques. Square
tubes up to 180mm x 180mm x 5.4mm and rectangular tubes up to 200 x 100 x 5.4mm are
commonly available.
4 Design using HSS
The sections are made with standard mild steel 0f grade E 250(410) with fy=250 mPa and
fu=410 mPa. As similar to hot rolled sections the sections are classified as plastic, compact, semi-
compact and sections according to thicknesses of web and flange. The following table provides the
classification
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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Member plastic compact emi.-
compact
Internal compression members 29 33.5 42
Web(general) 84 105 126
Circular tubes under moment or
Compression
42 52 146
b=B-3t. d=D-3t
4. Roofing cladding sheets
Roofing cladding sheets of the thin steel sheets available in roll from with the thickness up to
0.50mm are used to from roofing sheets. These sheet rolls are available indigenously with Bhutan
steels or with Tata Steels.. Large variety of these steel sheet possessing characteristics of
formability are imported from Australia, Taiwan, Malaysia and China.
Roofing and cladding sheets are formed with the sheets up to 0.60mm having an yield strength
250mPa or 550mPa in continuous preset rollers. These rollers shape the sheets to have ribs and
folds so that they can span a distance of distance of 2m with a live load of 1.0kN/sqm. Sheets can
also shaped to preset profiles with press forming. The ductility of sheets obtained by low carbon
contents allows them to be bent to intricate shapes and profiles. Figure indicates a standard
profiled metallic sheet.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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Profiled sheet
According to protection methods available they are classified in to three groups
1. Pre-painted galvanized sheets.
2. Zinc aluminum coated sheets.
3. Colour coated Zn – AL protected sheets.
4.1 Pre Painted Galvanized Iron Sheets
The rolls to be used for sheet forming are first given a coat of hot dipped zinc oxide coating
of 75 gms / sqm followed by a polyester paint coating with thickness of 27 microns – 200 microns,
over a silicon protective layer.
Sheets formed with these rolls can roof or clad the structures in moderate climates.
4.2Galvalume Sheets
The rolls of base steel are given a coat of silicon coating (1.5%), over which 43.5 zinc
oxide coating for sacrificial galvanic protection. The overlay coating of 55% of aluminum oxide is
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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provided for better barrier protection. The zinc – aluminum oxide coating is specified as an
amount of material deposited over a square meter surface as grams per square meter.(gsm)
In protected areas sheets with 75gms coating are used, while in normal building sheets with
coating intensity of 150gsm is common. In highly corrosive environments coating thickness of
200 gsm is preferred.
Sheet coating profile
4.3 Colour Coated Zn- Al Sheets
The protective capacity of these coated sheets are enhanced with a polyster paint coating of
25 -100 micron on either side. These paint also provide an attractive esthetic look for the external
and internal for buildings provided with these sheets.
4.4 Stand Alone or Clip Lock Sheets
Metal sheets are attached to purlins by self drilling screws. This type of fixing has
limitation of water leaking through the punctured holes.
Presently stand alone roof sheets or clipped roof sheets are available where in the
corrugated sheets are manually pressed and engaged over the clips attached to the purlins.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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Clip lock system
5 Pre Engineered Building Of shelf single stored industrial buildings where components
are made at a centralized factory transported and assembled are now available. In these
buildings 1)metal sheets for roofing and cladding, 2) Purlins ,Girt and sag rods, 3) Main frame,
4) Bracing system, 5) Gantry beams and (6) Mezzanine floors -act as integral structural metal
system.ered buildings coated metal sheets are used for roofing and side cladding needs. The
purlins are of cold formed Z purlins or lipped C purlins. The frames are un-braced gable
portal frames. These framed buildings use the steel in an optimum way. The building can be
extended at any time. The disadvantages included high convertibility cost of material and
heavy foundations to resist horizontal thrust. The horizontal thrust can be resisted long base
ties, floor anchored tie rods or heavy and deep foundations footings.Gable frame is made with
hot rolled I sections or tapered plate girder segments Up to 30m single bay frames are
preferred. Beyond 30m spans frames with intermediate columns are razorpreferred. The bay
spacing of frames may vary from 4.5m to 10m. The eaves height of frames where cranes are
not present is 4.5m to 5m. The eve‘s height for the frames where gantry girder bracket is
welded may vary up to 10m. The slope for pre-engineered gable frames may vary from 30 to
100.
The economy of the gable has been achieved with edge accuracy in fabrication just enough
material and connections to take care of design forces.. Since the section is made of plates the
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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variation is provided with continuously varying depth or varying plate thickness. Connections are
effected through slip critical high strength friction grip bolts. Portal frames made of castellated
sections and latticed frames .Latticed frames made of angles and pipes are also common.
In- plane stability of frame in provided with rigid joints effected through end plate
connections with high strength G.8.8 bolts. The transverse direction stability is provided with wall
and roof bracings.
The roof bracing in usually made of threaded steel rods. Rigid frames have no lateral
resistance normal to their plane. Stability in that direction is provided with side wall bracing.
Typical side wall bracing consists of steel rod or cable diagonals, eave strut and column on each
side.
Each flexural member purlin, frame truss or joint needs to be stable under all loads. The
compression flange of member under bending laterally tend to buckle and must be restrained by
proper bracing. Compression flange bracing for primary framing member is provided by roof
purlins, while top chord of the purlins get supported by roof sheet.
6. Bolt and Bolting
Bolts in steel structure are two type black bolts and high strength friction grip bolts. Bolts
are named as grade ( X .Y) where X denotes one tenth of ultimate strength of bolt material and Y
denotes the yield strength as a percentage of ultimate strength. For example grade 4.6 bolt will
have an ultimate strength 400 mpa and yield strength of 0.6 time 400 is 240 mpa.
High strength grip bolts are made fram alloy steel with grades from 8.8 to 10.9.In slip
critical bolted connections, bolts are installed and lightened to such a degree that large tensile
forces are induced in the bolts. These forces clamp the connected plates together. Applied shear
force is resisted by friction. If the applied shear force in less than the friction that develops
between two surfaces then no slip will occur. Nominal slip resistance of bolt in slip critical
connection.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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V = μf ns Kn Fo
Where V : Shear capacity, μf : Coefficient friction ( 0.3 to 0.5 ), ne: Number of surfaces .
while Kn: 1.0 for clearance holes .The maximum bolt tension values (Fo )of atandard bolts are
listed in the table below.
Failure of these connections is not sudden, since after slipping the connection supports the
loading through bearing.
Slip Critical Joints
7 Open Web Systems
In tension field method web of a plate girder can be thought as an imaginary truss. Except
areas of imaginary diagonal and vertical other portions of web are stressed to a meager value.
Open web systems are based on this concept. Solid web members are provided where needed, rest
of the areas is open. Open web systems are mainly lattice systems.
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7.1 Open Web Lattice Systems
In these structures web consist of simple angles or rods and they are pin connected to the
chords. Members carry axial forces either tension or compression. The lattice assembly may be
plane or space lattice For relatively lighter loads such as stringers in mezzanine floor and roof
purlins light gauge open web sections are preferred.
These sections have many advantages such as
1. Standardized depth and different loadings and can be pre fabricated.
2. They light and economical for the given load and span
Figure indicate open web sections used in practice. The major limitations are open web sections
cannot carry heavy shears or concentrated loads between supports.
In open web joist the bending moment is resisted by flange angles. The shear is resisted by bracing
rods
7.2 Triangular Built up Joists
Plane open web girders suffer from the disadvantage of lateral stability while under
erection and during service. Open web girders having a asymmetrical triangular cross section will
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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then be a better choice. These are linear space trusses with three parallel chords with three faces
having rod bracing lattices. The two inclined planes resist vertical shear and horizontal shear is
resists by all faces. Bending moments are resisted by chord members these members are natural
choice for purlins members. These members tied to chord members at three locations of chord are
efficient bracing elements.
7.3 Corrugated Webs:
Closely spaced stiffeners will enhance the shear strength against buckling. Following the
logic thin plates corrugated has been successfully employed for shear carrying function of plate
girders. Web plates as thin as 1.6 mm are being used in practice. Corrugation may be in sinusoidal
form or trapezoidal form. Corrugated web beams are built-up girders with thin corrugated web and
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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wide flange plates. Web corrugations of trapezoidal and sinusoidal corrugation have the advantage
where local buckling of flat strips is avoided.
Corrugated profile provides more stiffness against shear buckling. Due to local shell
behavior of the corrugated web the principal stresses caused by the shear are resisted by membrane
anchor developed in the web. Profiling of web generally avoids failure due to loss of stability
before plastic limit load is reached.
7.3.1 Sinusoidal Corrugation
Shear carrying capacity of sinusoidal corrugated web beam can be calculated as per the
equations in reference(3)
8 Flooring for Steel Framed Structures.
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8.1 Deck Sheets
A new simple to adopt roof casting is available with decking sheets. The slab is cast a
profiled steel sheering which with ribs . The steel decking act as formwork when the concrete is
fresh with no scaffolding and on hardening the deck acts as a composite beam in caring the load.
Figure 1 indicates a typical profiled sheet flooring (Fig. 1).
Figure 1 Typical Profiled Sheet Flooring
A composite deck arrangement and sections for sagging moments is shown in figure.
FIG.1 PROFILED SHEET FLOORING
FIG.2 RESITANCE OF SLAB DUE TO
SAGGING BENDING M OM ENT
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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8.2 Composite Beam Design.
The composite beam is formed by connecting the concrete slab supported on a profiled
steel sheering. The commonly used connector is the heated stud. The cross section used and
critical forces on the section are shown in figure 3.
F IG . 3 C O M P O S IT E B E A M
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9 Conclusion
A fee recent development in steel structural design and fabricatios are outlined.They are
just a poinder of many of the happening in the fast developing realm of steel structures. India, a
potential centre for economical fabrications , will see further more areas in this material adoption
for local and export markets.
References
1. Alexander Newman, Metal Building Systems., McGrew Hill Publications, Newyork,2005
2. Sheet Steel Design Hand book,SSAB Turnplat AB,Borlannge,Sweden,2004
3. Hassen K.Al Nageim and T.J.MaacGinley, Steel Structures,Taylor &Francis,London,2002.
4. Easley, Buckling Formulas For Corrugated Metal Diaphragms, Journal of ASCE Division,
ASCE No ST 7,July 1975, pp1403-1417.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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GOOD RCC CONSTRUCTION PRACTICE TO PREVENT CORROSION OF STEEL
Dr.K.JAGADEESAN*
*Principal, M.P.N.M.G Engineering College, Chennimalai
INTRODUCTION
The main concern and consideration in Civil Engineering are climate and its effects,
environmental and atmospheric conditions, properties and behaviour of metals and other materials
used. Studies on the damage, deterioration and durability of components attract the attention of
Civil Engineers of today. Among the most pressing concerns for structural concrete durability is
the corrosion of steel reinforcement.
Corrosion is defined as the destruction (or) deterioration of materials due to chemical (or)
electrochemical reaction with the environment, and means other than directly mechanical. The
corrosion of steel reinforcement is the depassivation of steel with the reduction in concrete
alkalinity through carbonation. Most of the materials undergo corrosion on exposure to natural
environments (like atmosphere, water and soil) and to other artificial environments (like gases,
liquids, moisture). Hazard to human life and economic losses occur due to premature deterioration
and destruction of buildings, bridges, culverts, pipes, structures including marine and offshore
structures, towers, water supply and sanitary fittings, carpentry and electrical fittings, implants for
human body, etc.
Deterioration of concrete due to corrosion results because the product of – ferric oxide,
brown in colour – occupies a greater volume (more than 2 to 10 times) than steel and exerts
substantial bursting stresses on the surrounding concrete. The outward manifestations of the
rusting include staining, cracking and spalling of concrete. The progress of corrosion process will
generally be in geometric progression with respect to time. Consequently, the c/s of the steel is
reduced. With time, structural distress may occur either by loss of bond between the steel and
concrete (or) due to cracking and spalling of concrete, (or) as a result of the reduced steel c/s area.
This latter effect can be of special concern in structures containing high strength pre-stressing steel
in which a small amount of metal loss could possibly induce tendon failure. However, the process
leading to the ultimate failure is slow and normally gives years of warning to the maintenance
engineering squad.
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DAMAGES DUE TO CORROSION
Formation of white patches
CO2 reacts with Ca(OH)2 in the cement paste to form CaCO3. The free movement of water
carries the unstable CaCO3 towards the surface and forms white patches.
- It indicates the occurrence of carbonation.
Brown patches along reinforcement
When reinforcement starts corroding, a layer of ferric oxide is formed. This brown product
resulting from corrosion may permeate along with moisture to the concrete surface without
cracking of the concrete.
Occurrence of cracks
The increase in volume exerts considerable bursting pressure on the surrounding concrete
resulting in cracking.
The hair line crack in the concrete surface lying directly above the reinforcement and
running parallel to it is the positive visible indication that reinforcement is corroding.
These cracks indicate that the expanding rust has grown enough to split the concrete.
Formation of multiple cracks
As corrosion progresses, formation of multiple layers of rust on the reinforcement which in
turn exert considerable pressure on the surrounding concrete resulting in widening of hair cracks.
In addition, a number of new hair cracks are also formed.
The bond between concrete and the reinforcement is considerably reduced. There will be a
hollow sound when the concrete is tapped at the surface with a light hammer.
Spalling of cover concrete
Due to loss in bond between steel and concrete and formation of multiple layers of scales,
the cover concrete starts peeling off.
At this stage, size of bars is reduced.
Snapping of bars
The continued reduction in the size of bars, results in snapping of the bars.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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This will occur in ties/stirrups first.
At this stage, size of the main bars is reduced.
Buckling of bars and bulging of concrete
The spalling of the cover concrete and snapping of ties causes the main bars to buckle.
This results in bulging of concrete in that region. This follows collapse of the structure.
When corrosion of reinforcement starts, the deterioration is usually slow but advances in a
geometrical progression.
Corrosion can also cause structural failure due to reduced c/s and hence reduced load
carrying capacity.
It is possible to arrest the process of corrosion at any stage by altering the corrosive
environment in the vicinity of the reinforcement.
PREVENTIVE MEASURES IN NEW CONSTRUCTIONS
Preventive measures for controlling corrosion of steel embedded in cement concrete use
sound corrosion engineering principles directed towards:
Design factors
(i) Low w/c ratio
(ii) High strength concrete
(iii) Higher minimum cement content
(iv) Higher concrete cover
(v) Proper detailing of reinforcement
(vi) Moderate stress levels
Construction aspects
(a) Adequate compaction of concrete
(b) Effective curing
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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(c) Production of impervious concrete
(d) Effective grouting of presented tendons
(e) Periodical maintenance
Reinforcement protection
Coating for reinforcement bars must
* Ensure uniform coating on the deformed surface configuration of the bars
* Be flexible enough to allow post-coated bending bars
* Be mechanically stable to sustain handling, transportation and fixing of reinforcement
* Provide facility of easy application
* Resist the corrosion
Protection to reinforcement in new construction
(a) Cement based coatings
(b) Galvanising/zinc based paints
(c) Epoxy coating
(d) Bitumen based paints
(e) Phosphatic coatings
Surface coating for concrete
Any coating selected to be applied on the concrete surface as a preventive measure for
corrosion of reinforcement, shall perform the following functions.
(a) Controlling carbonation of concrete
(b) Resistance of chloride penetration
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(c) Control of moisture content of concrete
(d) Supplementary protection in case of inadequate cover
(e) Protect concrete from sulphate attack
(f) Protect reinforcement from corrosion
In addition, any paint system used as coating for concrete should possess the following
properties:
(a) Adhesion to concrete surface
(b) Alkali resistance
(c) Abrasion resistance
(d) Flexible/Viscous
(e) Weather resistance
(f) Carbon dioxide diffusion resistance
(g) Water vapour diffusion
(h) Water penetration resistance
(i) Chloride/sulphate penetration resistance
Based on the above functional requirements and other properties surface coating materials
can be classified as follows
BitumensElastomers
(a) Polymers
(b) Silicones
(c) Silanes
(d) Vegetable oils
REMEDIAL MEASURES FOR EXISTING STRUCTURES
Rehabilitation of reinforced concrete structures, affected by the corrosive environments
could be achieved effectively if the factors influencing the durability of the structure and the extent
of damage are investigated systematically and various problems and causes afflicting the structure
are isolated.
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PHYSICAL INSPECTION
Cracks appearing in concrete along the reinforcement, spalling of concrete, tilting of
structures, excessive deflections, crazy formation on concrete surface indicating carbonation, etc.,
can be relied upon to give sufficient data. While making visual inspection those affected due to
corrosive environment should be differentiated from those showing deterioration due to structural
inadequacy.
INSPECTION OF RECORDS
A study of architectural and structural designs pertaining to the structure under
investigation, helps to isolate such features which are more prone to corrosive environment. The
structural drawings could help in arriving at the expected life span of the building apart from
helping to assess the nature and extent of treatment to rehabilitate the structure.
Corrosion monitoring techniques
(a) Non-destructive tests
(i) Rebound hammer test
* To evaluate compressive strength of the affected portion and the same could be correlated
with the designed strength of the element of the structure.
(ii) Ultra-sonic pulse-velocity test
* To investigate extent and depth of deep rooted cracks.
* An ultra-sonic pulse with help of a transmitter and receiving the same on the opposite face
with the help of a receiver.
* The measurement of velocity of sound can indicate the detour taken by the sound due to
presence of cracks in the structure and location/depth of the crack could be monitored on a
cathode ray oscilloscope. Fig. 9 and Fig. 10 show the ultra-sonic test.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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(iii) Potential measurement
Under favourable condition it is possible to use electrical measurements from surface of
concrete to get an indication of the condition of steel inside. Electrical connection will have to be
made with rebar by making a small hole in concrete. Electrical connection with concrete is made
by means of an electrolyte which wets both concrete and conductor to which another wire is
attached. The electrolyte and conductor are made into a probe which can be held against concrete
surface. Fig. 11 shows the half cell potential process.
The following three electrodes are used:
1. Saturated calomel electrode
2. Silver/Silver chloride elctrode
3. Copper/Copper sulphate electrode
As per ASTM standards, the probability of corrosion is as follows: [ASTM 1989]
Half-cell potential Probability
mV vs CSE (Percent)
(Copper/Copper sulphate electrode)
More negative than – 350 90
Between –350 and –200 uncertain
More positive than –200 10
However, in combination with resistivity measurements and resistivity contours the equi-
potential maps will help in assessment of corrosion. In this technique, the corrosion cell ratio is
determined as follows:
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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Corrosion cell ratio =
Maximum difference in potential between
the cathodic and anodic regions
Average electrical resistivity in the
anodic region
Active corrosion in the anodic region is probable in cases where this ratio is not less than 5.0.
(b) Destructive tests
Core samples could be obtained from the affected part with the help of core cutting
machines and compressive strength could be found out. This compressive strength of core after
appropriate modifications, could be compared with the standard cube results of the originally laid
concrete after allowing for age factor.
Concrete cubes could also be prepared from the damaged concrete and after capping etc.,
the same could be tested for compressive strength. The results after correcting for cube size can be
compared with the compressive strength of concrete as known from design considerations.
Specimen of exposed rebars could be taken and tested for metallurgical properties and
tensile characteristics.
Carbonation test
* To find the extent of carbonation in a concrete member.
* It indicates the loss of alkalinity and reduction in the pH value below the corrosion
threshold limit of the cover concrete
* A pH indicator solution of phenolphthalein in dilute alchohol is sprayed on a freshly
concrete surface.
* The pH indicator changes colour according to the alkalinity of the concrete.
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* As pH value decreases from 10.0 to 8.2 and below, the indicator changes from dark pink to
colourless informing that the concrete has carbonated.
REMEDIAL MEASURES
The methods of repairs to be adopted should be specifically suited to arrest further
corrosive action of the environment; which almost invariably continue to ravage the structure even
after its rehabilitation. Some of the important methods of repair to concrete structures damaged by
corrosive environment are given below
Fig.13 & 14 shows the steps of repair techniques of structural member deterioration due to
corrosion.
Step 1 : Hammer testing the concrete surface for cavities and chiseling of all loose portions
to expose the sound core concrete and expose the rusted reinforcement.
Step 2 : Clean rusted reinforcement and exposed concrete surface by sand blasting,
mechanical devices (or) any other established methods.
Step 3 : Application of two coats of mineral based polymer modified corrosion inhibiting
primer colusal mix. Colusal 25 (or) equivalent.
Step 4 : Appliaction of two component polymer based bond coat zentrifix HB + Nafufil BB
2 (or) equivalent.
Step 5 : Application of polymer modified ready to use mortar zentrifix as + Nafufill BB 2
(or) mortar of low permeability (or) guniting with guniting aid.
Step 6 : Application of carbonation resistant, polymer modified, ready to use fine mortar,
Naf liquid + Nafufill BB 2 (or) zentrifix HB + Nafufill BB 2 over the whole
surface.
Step 7 : Final protection coat to concrete depending upon protection required. Nisiwash or
emcecol (or) flex (or) zentrifix – elastic + emcecol (or) equivalent.
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CONCLUSIONS
Based on a critical review and analysis of various causes which influence durability of
reinforced cement concrete structures, the following points should be emphasized during design,
construction and maintenance stages to enhance the life of important reinforced concrete
structures.
1. At the planning, designing and construction stages environment should be accounted for,
so that concrete is able to perform the service for which it has been designed.
2. Use of dense concrete of as high a grade (above M-20) and with adequate cover over
reinforcement should be ensured.
3. Avoid congestion of reinforcement at joints and ensure proper detailing of joints.
4. Use coated steel as reinforcement for conditions exposed to serious attack.
5. Periodical non-destructive testing for assessing the progressive degree of damage under the
cumulative deleterious effect of aggressive media should be carried out.
6. Minimum construction and expansion joints should be provided in the structure.
7. Approaches for inspection facilities to all important places of deterioration must be
included in the design stage.
8. Periodical maintenance of structures shall be carried out.
9. Cover to diameter c/d ratio should be kept above 2.0 for good performance.
10. Under similar conditions Tor Steel corrodes more than Mild steel.
11. Beams exposed to corrosion environment should be provided with at least 25% excess
shear capacity so that unfavourable shear failure at later ages is avoided.
12. W/c ratio > 0.5 should be never be used. It is recommended that w/c ratio is limited to 0.4
for important structures in the coastal areas.
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REFERENCES
1. Dr. A. R. Santhakumar and K. Jagadeesan, ―Corrosion resistance of chemical coatings‖ –
A short-term course on ―Corrosion damage, maintenance and Rehabilitation of Structures‖,
Anna University, Madras, April 1995.
2. Dr. R. Jagadish, ―Corrosion in reinforced concrete structures‖, Bangalore University,
Bangalore
3. Dr. S. Chandrasekaran, ―Corrosion in Civil Engineering‖, C.E.C.R.T., Madras.
4. Prof. P. Kalyanasundaram, ―Assessment of Concrete Deterioration and Corrosion
Damage‖, I.I.T., Madras.
CONCRETE BUILDING
GROWING RUST
CATHODE ANODE CATHODE
Steel Reinforcement
CONCRETE
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Fig. 2(a) Formation of Protective Skin Around Steel
Fig.2(b) Typical Case of Potential Difference in the Ties of Column
OXYGEN DENSE CONCRETE (ANODE)
CHLORIDES MOISTURE POROUS CONCRETE
(CATHODE)
CARBON- DENSE CONCRETE (ANODE)
DIOXIDE
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Fig.2(c) Typical Case of Potential Difference in
Concrete
H2 EVOLUTION BEGINS
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
051015
pH
Co
rro
sio
n R
ate
(in
/yr)
Acid neutral alkaline
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Protective coating
required over concrete
in the case of very
severe attack by acid
media
CaCO3
Carbo-
nated
concrete
Ca(OH)2
alkaline concrete
“active corrosion”
protection for rein
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Fig.4 Carbonation Process
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Fig.6 Chloride Induced Macro Cell Corrosion of Steel in Concrete
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Fig.7 (not to be scaled)
Fig.8
0
10
20
30
40
50
60
0 20 40 60 80 100
TIME (days)
CA
RB
ON
AT
ION
DE
PT
H (
mm
)
w/c=0.35
w/c=0.65
w/c=0.50
w/c=0.80
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RE O
TR
L1
L2
L3
L1 L2 L3 O
INPUT OUTPUT
TR
RE crack
TR
RE
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Fig.9 Ultra-Sonic Test
1 2 1 2 3
Oscillosco
pe
Screen
Uncracked
Specimen
Cracked
Specimen
(a)
(A)
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ULTRASONIC WAVEFORM RECEIVED FROM:
(a) an undamped specimen
(b) damped speciman
Fig.10 Ultra-Sonic Test
(b)
(A’)
+ - -0.244
HIGH IMPENDENCE VOLTMETER
COPPER/COPPER SULPHATE
REFERENCE ELECTRODE
CONCRETE COVER
REINFORCEMENT
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Fig.11 Half-Cell Potential
Fig.12 Cathodic Protection
Current Source
Pipe being
protected
Sacrificial anode
Conducting back fill
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STEP-1 STEP-2
STEP-4 STEP-5
STEP-7 STEPS 3 TO 5 SAME AS BEFORE
Ld Ld
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Reinforcement Steel
Unsound concrete and areas over corroded
reinforcement are removed
Concrete broken out
Area of steel reinforcement to be treated
with a protective coat
Carbonated concrete
Noncorbonated concrete (solid)
COLUMN/
BEAM/
SLAB
Fig 13 (Contd.)
Fig 13 (Contd.)
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SMART MATERIALS AND SMART STRUCTURES
Dr.E.B.PERUMAL PILLAI
Professor of Civil Engineering
Coimbatore Institute of Technology
COIMBATORE – 641 014
email : [email protected]
Introduction:
Civil infrastructures, such as buildings and bridges, are an integral part of modern
civilization. Conventionally, these structures were designed to resist static loads. But however they
are subjected to a variety of dynamic loadings, including winds, waves, earthquakes etc. These
dynamic loads can cause severe and/or sustained vibratory motion, both of which are detrimental
to the structure. Recent earthquakes resulted in huge property damage and loss of lives which
remind us the vulnerability to natural hazards. The control of structures subjected to such
excitation represents a challenging task for the structural engineers. Hence the development of
safer civil structures to better resist these hazards is of prime importance. That results in the
evolution of the new concept Smart Structural Systems. These systems are built with smart
materials, which behave intelligently save the lives and result in minimum damage to properties.
The development of durable and cost effective high performance construction materials and
systems is important for the economic well being of a country mainly because the cost of civil
infrastructure constitutes a major portion of the national wealth. To address the problems of
deteriorating civil infrastructure, research is very essential on smart materials. This paper
highlights the use of smart materials for the optimal performance and safe design of buildings and
other infrastructures particularly those under the threat of earthquake and other natural hazards.
The peculiar properties of the shape memory alloys for smart structures render a promising area of
research in this field.
Smart Materials:
With the development of materials and technology, many new materials find their
applications in civil engineering to deal with the deteriorating infrastructure. Smart material is a
promising example that deserves a wide focus, from research to application. With two crystal
structures called Austenite and Martensite under different temperatures, smart material exhibits
two special properties different from ordinary steels. One is shape memory, and the other is
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superelasticity. Both of these two properties can suit varied applications in civil engineering, such
as prestress bars, self-rehabilitation, and two-way actuators, etc.
Until relatively recent times, most periods of technological development have been linked
to changes in the use of materials (eg the stone, bronze and iron ages). In more recent years the
driving force for technological change in many respects has shifted towards information
technology. This is amply illustrated by the way the humble microprocessor has built intelligence
into everyday domestic appliances. However, it is important to note that the IT age has not left
engineered materials untouched, and that the fusion between designer materials and the power of
information storage and processing has led to a new family of engineered materials and structures.
Dumb Materials:
Most familiar engineering materials and structures until recently have been ‗dumb‘. They
have been preprocessed and/or designed to offer only a limited set of responses to external stimuli.
Such responses are usually non-optimal for any single set of conditions, but ‗optimised‘ to best
fulfil the range of scenarios to which a material or structure may be exposed. For example, the
wings of an aircraft should be optimised for take-off and landing, fast and slow cruise etc.
However, despite the partial tailoring of these structures by the use of additional lift surface, which
we see deployed as each passenger aircraft approaches an airport, such engineering components
are not fully optimised for any single set of flight conditions. Similarly, advanced composites such
as glass and carbon fibre reinforced plastics, which are often thought to be the most flexible
engineering materials since their properties (including strength and stiffness) can be tailored to suit
the requirements of their end application, can only be tailored to a single combination of
properties.
Biomimetics:
‗Dumb‘ materials and structures contrast sharply with the natural world where animals and
plants have the clear ability to adapt to their environment in real time. The field of biomimetics,
which looks at the extraction of engineering design concepts from biological materials and
structures, has much to teach us on the design of future manmade materials. The process of
balance is a truly ‗smart‘ or intelligent response, allowing, in engineering terms, a flexible
structure to adapt its form in real time to minimise the effects of an external force, thus avoiding
catastrophic collapse.
The natural world is full of similar properties including the ability of plants to adapt their
shape in real time (for example, to allow leaf surfaces to follow the direction of sunlight), limping
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(essentially a real time change in the load path through the structure to avoid overload of a
damaged region), reflex to heat and pain. The materials and structures involved in natural systems
have the capability to sense their environment, process this data, and respond. They are truly
‗smart‘ or intelligent, integrating information technology with structural engineering and actuation
or locomotion.
Smart structural applications are the currently exploring topic of investigation in resisting
the natural hazards. The research is carried out in two diversified areas such as health monitoring
of structures and the control of the structures. The first system is the one in which the entire
structural component is monitored which gives you the complete status of the health of the
structure. The second is more specific testing, in which quantitative values are analyzed at
different locations and the damage then completely identified in respect of size, location and
severity and appropriate action is taken to revive the structure and put back in use. These systems
involve materials with embedded or surface mounted sensors whose information is controlled and
processed by computer controlled system, which directs the actuator to perform the remedial
action.
The above said concepts are made possible by the latest development in the field of Fiber
optic materials, Piezoelectric materials, Shape memory alloys, ER and MR fluids etc., Out of the
identified materials fiber optic and piezoelectric materials gain widespread acceptance and are
widely used in health monitoring/ sensing. Whereas Piezoceramics, Shape Memory Alloy, Electro-
and Magneto- Rheological fluids are used in the field of smart control/actuation. The various
materials are described below briefly.
Fiber Optic Sensors:
Earlier Fiber Optic Sensors are very much used in the communication industry. But today
they are extended to civil engineering structures as one of the candidate sensing material. The
advantages are immunity to electro-magnetic interference, small size, lightweight and
compatibility with the host material. To add remote sensing is easily accomplished and the sensed
information transmitted by optical fibers to a remote site for evaluation.
The different type of Fiber optic Sensors used in practice are
Optical Time Domain Reflectometry (OTDR)
Fiber Optic Polarimetric Sensor (FOPS).
Extrinsic Fabry-Perot Interferometric sensor (EFPI)
Bragg Grating strain sensor.
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Piezoelectric Materials:
Piezoelectricity is the ability of a material to develop an electrical charge when subjected to
a mechanical strain (direct piezoelectric effect) and conversely, develop mechanical strain in
response to an applied electric field (converse piezoelectric effect).The coupled mechanical and
electrical properties of piezoelectric materials make them well suited for use as sensors and
actuators. As a sensor, deformations caused by the dynamic disturbance, the structure produce an
electric charge resulting in an electric current in the sensing circuit, while as an actuator, a high
voltage signal is applied to the piezoelectric device, which deforms the actuator and transmits
mechanical energy to the host structure. Piezoelectric materials have been found to be very
attractive for smart structure applications. Piezoelectric materials are light and can be readily
attached or embedded in structures. They are suitable as distributed sensors and actuators
The two common types of piezoelectric materials
Lead Zirconate Titanate (PZT) ceramics
Polyvinylidene fluoride (PVDF) polymers
They are usually produced in thin sheets with films of metal deposited on the opposite surfaces to
form electrodes. Piezoceramics are brittle and stiff, while piezopolymers are tough and flexible. In
particular piezopolymers are good candidates for sensing because of their small stiffness, while
piezoceramics are better suited for actuating due to their greater elastic modulus for effective
mechanical coupling to the structure.
Materials and Application:
Shape Memory Alloys (SMA) :
A shape memory alloy (SMA) is able to memorize and recover its original shape, after
deformed by heating over its transformation temperature. During this transformation, large forces
or large deformations can be generated which can be used for actuation. The advantage of using
SMA is that after severe deformation, SMA can still fully return its original shape. Nitinol (Nickel
- Titanium Alloy) is the most commonly used SMA. The drawbacks of SMA based actuators are
comparatively slow response time. SMAs are not suitable for high-frequency control, but can be
used for low frequency and quasi-static response control.
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The term shape memory refers to the ability of certain alloys (Ni – Ti, Cu – Al – Zn etc.)
to undergo large strains, while recovering their initial configuration at the end of the
deformation process spontaneously or by heating without any residual deformation .The
particular properties of SMA‘s are strictly associated to a solid-solid phase transformation
which can be thermal or stress induced. Currently, SMAs are mainly applied in medical
sciences, electrical, aerospace and mechanical engineering and also can open new
applications in civil engineering specifically in seismic protection of buildings.
Its properties which enable them for civil engineering application are
1. Repeated absorption of large amounts of strain energy under loading without
permanent deformation. Possibility to obtain a wide range of cyclic behaviour –
from supplemental and fully recentering to highly dissipating-by simply varying
the number and/or the characteristics of SMA components.
2. Usable strain range of 70%
3. Extraordinary fatigue resistance under large strain cycles
4. Their great durability and reliability in the long run.
Structural Uses:
The development of durable and cost effective high performance construction
materials and systems is important for the economic well being of a country mainly because
the cost of civil infrastructure constitutes a major portion of the national wealth. To address
the problems of deteriorating civil infrastructure, research is very essential on smart
materials. The peculiar properties of the shape memory alloys for smart structures render a
promising area of research in this field.
1).Active control of structures :
The concept of adaptive behavior has been an underlying theme of active control of
structures which are subjected to earthquake and other environmental type of loads. The
structure adapts its dynamic characteristics to meet the performance objectives at any instant
2).Passive control of structures :
Two families of passive seismic control devices exploiting the peculiar properties of
SMA kernel components have been implemented and tested within the MANSIDE project
(Memory Alloys for New Seismic Isolation and Energy Dissipation Devices). They are
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Special braces for framed structures and isolation devices for buildings and bridges.
Fig.1.shows the arrangement of SMA brace in the scaled frame model and the reduced scale
isolation system.
Fig-1
3) Smart Material Tag :
This smart material tag can be used in composite structures. These tags can be
monitored externally throughout the life of the structure to relate the internal material
condition. Such measurements as stress, moisture, voids, cracks and discontinuities may be
interpreted via a remote sensor.
4) Retrofitting :
SMAs can used as self-stressing fibres and thus they can be applied for retrofitting.
Self-stressing fibres are the ones in which reinforcement is placed into the composite in a
non-stressed state. A prestressing force is introduced into the system without the use of large
mechanical actuators, by providing SMAs. These materials do not need specialized electric
equipments nor do they create safety problems in the field. Treatment can be applied at any
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time after hardening of the matrix instead of during its curing and hardening. Long or short
term prestressing is introduced by triggering the change in SMAs shape using temperature or
electricity.
5) Self-healing :
Experimentally proved self-healing behavior (5) which can be applied at a material
micro level widens their spectrum of use. Here significant deformation beyond the first crack
can be fully recovered and cracks can be fully closed.
6) Self-stressing for Active Control :
Can be used with cementitious fibercomposites with some prestess, which impart self-
stressing thus avoiding difficulties due to the provision of large actuators in active control
which require continuous maintenance of mechanical parts and rapid movement which in turn
created additional inertia forces. In addition to SMA‘s some other materials such as polymers
can also be temporarily frozen in a prestrained state that have a potential to be used for
manufacturing of self-stressing cementitious composites.
7.Structural Health Monitoring :
Use of piezo transducers, surface bonded to the structure or embedded in the walls of
the structure can be used for structural health monitoring and local damage detection.
Problems of vibration and UPV testing can be avoided here.
8)Substitute for steel:
It is reported that the fatigue behaviour of CuZnAl-SMA‘s is comparable with steel. If
larger diameter rods can be manufactured, it has a potential for use in civil engineering
applications. Use of fibre reinforced plastics with SMA reinforcements requires future
experimental investigations.
9)ER and MR Fluids:
Electrorheological (ER) dampers typically consist of a hydraulic cylinder containing micron-
sized dielectric particles suspended within a fluid (usually oil). In the presence of a strong electric
field, the particles polarize and become aligned, thus offering an increased resistance to flow. By
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varying the electric field, the dynamic behavior of an ER damper can be modulated. As the applied
electric field increases, the behavior of ER fluids changes from that of a viscous fluid to that of a
yielding solid within milliseconds. Magnetorheological (MR) dampers are essentially magnetic
analogs of ER dampers. Qualitatively, the behavior of the two types of dampers is very similar
except that the control effect is governed by the application of an electric field in one case and by a
magnetic field in the other. MR dampers typically consist of a hydraulic cylinder containing
micron-sized, magnetically polarizable particles suspended within a fluid (usually oil). MR fluid
behavior is controlled by subjecting the fluid to a magnetic field. In the absence of a magnetic
field, the MR fluid flows freely while in the presence of a magnetic field, the fluid behaves as a
semisolid. MR fluids are made of micron-sized particles which under the influence of magnetic
field form long chains, which can alter the Rheological properties such as viscosity and yield stress
of the fluids. The advantages of MR fluids include fast response times, high dynamic yield stress,
low plastic viscosity and broad operational temperature range.
10)Smart Structural Systems :
Smart Structural Systems are defined as structural systems with a certain-level of autonomy
relying on the embedded functions of sensors, actuators and processors, that can automatically
adjust structural characteristics, in response to the change in external disturbance and
environments, toward structural safety and serviceability as well as the elongation of structural
service life.
General Requirements and Expectations of smart structural systems are given below.
a) High degree of reliability, efficiency and sustainability not only of the structure but also of
the whole system.
b) High security of the infrastructures particularly when subjected to extreme and
unconventional conditions.
c) Full integration of all the functions of the system.
d) Continuous health and integrity monitoring.
e) Damage detection and self-recovery.
f) Intelligent operational management system.
Smart Technologies Prospects
a) New sensing materials and devices.
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b) New actuation materials and devices.
c) New control devices and techniques.
d) Self-detection, self-diagnostic, self-corrective and self-controlled functions of smart
materials/systems.
Sensors and Actuators:
Actuation can be produced by controlling devices such as actuators, pumps, heaters and
dampers, and by a number of new materials. For active noise control applications, microphones
are used as acoustic sensors and loudspeakers as acoustic actuators. For displacement and velocity
control, two types of transducers are convenient: Linear Variable Differential Transformers
(LVDT) and Linear Variable Inductance Transformers (LVIT). Other devices are also available—
accelerometers and two basic types of actuators. Hydraulic and pneumatic actuators are employed
when low frequency, large force and displacements are required, while the electromagnetic/ shaker
types are utilized to react against an inertial electrodynamic mass.
Command and Control Unit:
The command and control unit is the manager of day-to-day operations, responsible for
monitoring the health and integrity of the system by means of a communication network which
works in real time. The unit operates by controlling a compendium of integrated non-destructive
evaluation instruments, by managing optical fibre sensors and actuators, or by overseeing
operational and control devices. This is the brain of the smart structure and has two basic and
distinct functions.
The Processing Function: This function receives information; analyses it; sorts, arranges and
classifies it; and stores and/or processes it depending on the nature, frequency and quality of the
data and its origins. All these previous operations are dealt with by intelligent or smart processing,
with or without human intervention, and with little or no human interaction. Special algorithms
can be used to control the behaviour or detect damage. Pattern recognition algorithms, as well as
neural networks with fuzzy logic can be efficiently employed to process the raw data. Finally,
expert systems can handle the retrieval, management, classification, and storage of the data.
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The Analysis Function: This function deals with the detailed examining of the raw data in an
intelligent way. Using the analysis outlined above, it will exploit the results to assess the condition
of the structure. This analysis consists of localizing and identifying specific variables, items or
features as compared to threshold levels defined in advance, or specified in codes, rules,
regulations or standards. When an adverse condition is detected and the appropriate corresponding
conclusion is reached, decisions for action are sent to the action controlling devices, which will be
triggered to react. Special algorithms are developed to operate these functions.
Fig 2 Smart Structural System
Structural Control:
The control of structures subjected to dynamic excitation represents a challenging task for
the civil engineering profession. Structural control for civil structures was born out of a need to
provide safer and more efficient designs. The purpose of structural control is to absorb and to
reflect the energy introduced by dynamic loads. The total amount energy is estimated by the
following relation
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E = Ek +Es +Eh+ Ed (1.1)
E = The total energy input
Ek = Kinetic energy of the structure
Es = Elastic strain energy
Eh = Energy dissipated due to inelastic deformation
Ed = Energy dissipated by supplemental damping devices
Based on the above the various newer concepts of structural control have emerged and have
been gaining acceptance as an efficient structural system.
Structural Control involves basically the regulation of pertinent structural characteristics as
to ensure desirable response of the structure under the effect of its loadings. The control can be
exerted by using either active or passive control mechanisms or both. These mechanisms provide
in general a system of auxiliary forces, the so- called control forces. These forces are designed so
that they regulate continuously the structural response. The structural control mechanisms may be
active or passive mechanism.
(i) Passive Control Mechanisms:
Passive control mechanisms operate without using any external energy supply. They use the
potential energy generated by the structure‘s response to supply the control forces. In this case, the
control forces are only able to control the structure‘s response up to a certain limit imposed by the
lack of energy needed to tackle larger responses. In the areas of passive systems, they include Base
Isolation Systems, Tuned Mass system and Fluid damper system and a variety of mechanical
energy dissipaters.
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(ii) Active Control Mechanisms:
Active control mechanisms operate by using an external energy supply. Therefore, they are
more efficient than the passive control mechanisms because they can control displacement,
velocity, and acceleration of the structure to any extend. Most of the active Control mechanisms
can operate also as passive ones if the supplied control energy is stopped.
Active Structural Control:
Active control systems are force delivery devices integrated with real time processing
evaluators/ controllers and sensors within the structures. They act simultaneously with the
hazardous excitation to provide enhanced structural behaviour for improved service and safety.
Fig. shows the structure with different control schemes.
An active structural control system has the basic configuration consisting of the following
as shown in Fig 3.
a) Sensors located about the structure to measure either external excitations or structural response
variables or both, provides the signal needed to actuate the controller. The commonly used sensors
are the deflection sensor, the velocity sensor and the acceleration sensor.
b) Devices to process the measured information and to compute the necessary control force
needed based on a given control algorithm.
c) Actuators, usually powered by external sources, to produce the required forces. They can be an
electro-hydraulic servomechanism or proportional gain controller or an automatic gain controller.
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Fig. 3 Structural Control
When only the structural response variables are measured, the control configuration is
referred to as feedback control since the structural response is continuously monitored and this
information is used to make continual correction to the applied control forces. A feed forward
control results when the control forces are regulated only by the measured excitation. In the case
where the information on both the response quantities and excitation are utilized for control
design, the term feed back – feed forward control is used.
Carbon Fibre Reinforced Concrete (CFRC)
Its ability to conduct electricity and most importantly, capacity to change its conductivity
with mechanical stress makes a promising material for smart structures .It is evolved as a part of
DRC technology(Densified Reinforced Composites).The high density coupled with a choice of
fibres ranging from stainless steel to chopped carbon and kelvar, applied under high pressure gives
the product with outstanding qualities as per DRC technology. This technology makes it possible
to produce surfaces with strength and durability superior to metals and plastics.
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Smart Concrete
A mere addition of 0.5%specially treated carbon fibres enables the increase of electrical
conductivity of concrete. Putting a load on this concrete reduces the effectiveness of the contact
between each fibre and the surrounding matrix and thus slightly reduces its conductivity. On
removing the load the concrete regains its original conductivity. Because of this peculiar property
the product is called ―Smart Concrete‖. The concrete could serve both as a structural material as
well as a sensor.
The smart concrete could function as a traffic-sensing recorder when used as road
pavements. It has got higher potential and could be exploited to make concrete reflective to radio
waves and thus suitable for use in electromagnetic shielding. The smart concrete can be used to
lay smart highways to guide self steering cars which at present follow tracks of buried magnets.
The strain sensitive concrete might even be used to detect earthquakes.
Active railway track support
Active control system for sleepers is adopted to achieve speed improvements on existing
bridges and to maintain the track in a straight and non-deformed configuration as the train passes
With the help of optimal control methodology the train will pass the bridge with reduced track
deflections and vibrations and thus velocity could be safely increased.
Active structural control against wind
Aerodynamic control devices to mitigate the bi-directional wind induced vibrations in tall
buildings are energy efficient, since the energy in the flow is used to produce the desired control
forces. Aerodynamic flap system(AFS) is an active system driven by a feedback control algorithm
based on information obtained from the vibration sensors(3).The area of flaps and angular
amplitude of rotation are the principal design parameters.
Applications of Smart Materials
There are many possibilities for such materials and structures in the man made world.
Engineering structures could operate at the very limit of their performance envelopes and to their
structural limits without fear of exceeding either. These structures could also give maintenance
engineers a full report on performance history, as well as the location of defects, whilst having the
ability to counteract unwanted or potentially dangerous conditions such as excessive vibration, and
effect self repair. The Office of Science and Technology Foresight Programme has stated that
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`Smart materials ... will have an increasing range of applications (and) the underlying sciences in
this area ... must be maintained at a standard which helps achieve technological objectives', which
means that smart materials and structures must solve engineering problems with hitherto
unachievable efficiency, and provide an opportunity for new wealth creating products.
Smart Materials in Aerospace
Some materials and structures can be termed ‗sensual‘ devices. These are structures that
can sense their environment and generate data for use in health and usage monitoring systems
(HUMS). To date the most well established application of HUMS are in the field of aerospace, in
areas such as aircraft checking.
An airline such as British Airways requires over 1000 employees to service their 747s with
extensive routine, ramp, intermediate and major checks to monitor the health and usage of the
fleet. Routine checks involve literally dozens of tasks carried out under approximately 12 pages of
densely typed check headings. Ramp checks increase in thoroughness every 10 days to 1 month,
hanger checks occur every 3 months, ‗interchecks‘ every 15 months, and major checks every
24000 flying hours. In addition to the manpower resources, hanger checks require the aircraft to be
out of service for 24 hours, interchecks require 10 days and major checks 5 weeks. The overheads
of such safety monitoring are enormous.
An aircraft constructed from a ‗sensual structure‘ could self-monitor its performance to a
level beyond that of current data recording, and provide ground crews with enhanced health and
usage monitoring. This would minimise the overheads associated with HUMS and allow such
aircraft to fly for more hours before human intervention is required.
Smart Materials in Civil Engineering Applications
However, ‗sensual structures‘ need not be restricted to hi-tech applications such as aircraft.
They could be used in the monitoring of civil engineering structures to assess durability.
Monitoring of the current and long term behaviour of a bridge would lead to enhanced safety
during its life since it would provide early warning of structural problems at a stage where minor
repairs would enhance durability, and when used in conjunction with structural rehabilitation
could be used to safety monitor the structure beyond its original design life. This would influence
the life costs of such structures by reducing upfront construction costs (since smart structures
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would allow reduced safety factors in initial design), and by extending the safe life of the structure.
‗Sensual‘ materials and structures also have a wide range of potential domestic applications, as in
food packaging for monitoring safe storage and cooking.
The above examples address only ‗sensual‘ structures. However, smart materials and
structures offer the possibility of structures which not only sense but also adapt to their
environment. Such adaptive materials and structures benefit from the sensual aspects highlighted
earlier, but in addition have the capability to move, vibrate, and exhibit a multitude of other real
time responses.
Potential applications of such adaptive materials and structures range from the ability to
control the aeroelastic form of an aircraft wing, thus minimising drag and improving operational
efficiency, to vibration control of lightweight structures such as satellites, and power pick-up
pantographs on trains. The domestic environment is also a potential market for such materials and
structures, with the possibility of touch sensitive materials for seating, domestic appliances, and
other products. These concepts may seem ‗blue sky‘, but some may be nearing commercial
readiness as you read this.
Mechatronics
Approaches vary from the use of mechatronics (essentially hybrid mechanical/electronic
systems) to the development of truly smart materials, where sensing and actuation occurs at the
atomic or molecular level. The mechatronic approach is familiar from systems already in existence
such as ABS and active ride control in road vehicles, and such an approach has already been
employed in the vibration control of high rise Japanese buildings. However, in truly smart
structures the integration of sensing and actuation is generally greater than that in pure
mechatronic systems, with the required function integrated within the structural material itself.
Such structures have been compared to Frankenstein's monster since separate sensors and
actuators are integrated (or bolted) together into a structural material, but without the materials
themselves being smart. Examples include sensual structures containing optical fibre sensors for
monitoring load history and damage accumulation in bridges, dams and aircraft and adaptive
structures containing novel piezoceramic, electrostrictive, magnetostrictive and shape memory
actuators, for real time vibration and shape control.
Ken Materials
‗ Mechatronic‘ smart structures have demonstrated the capability of this technology, but
raise the important issue of the complexity of the resulting system. These smart structures contain
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a multitude of different materials, and in the case of sensual structures will generate large amounts
of data. This increase in complexity has been described by Hiroaki Yanagida as the ‗spaghetti
syndrome‘, and has led to the proposal for an alternative type of smart structure based on the
concept of ken materials (the Chinese characters meaning wisdom, structure, monitoring,
integration and benignity being pronounced ken in the Japanese language). Such structures would
move functional integration into the constituent engineering materials themselves.
Few practical examples of ken materials exist at present, although a structural composite
based on this concept has been developed in Japan. This is a carbon and glass fibre reinforced
concrete which is able to monitor concrete structures using only the structural reinforcing fibres,
thus reducing the complexity of the system.
At the Atomic Level
The ultimate integration is a level beyond ken materials where functionality occurs at the
microstructural or atomic and molecular scale. This produces what is commonly known as a
‗smart material‘. Few examples of true smart materials exist at present, although the function of
such a material can be illustrated by the familiar photochromic glass. Such glasses have inbuilt
sensing and response but have only one response to the one stimulus.
The Future
The development of true smart materials at the atomic scale is still some way off, although
the enabling technologies are under development. These require novel aspects of nanotechnology
(technologies associated with materials and processes at the nanometre scale, 10-9
m) and the newly
developing science of shape chemistry.
Worldwide, considerable effort is being deployed to develop smart materials and
structures. The technological benefits of such systems have begun to be identified and,
demonstrators are under construction for a wide range of applications from space and aerospace, to
civil engineering and domestic products. In many of these applications, the cost benefit analyses of
such systems have yet to be fully demonstrated.
The Office of Science and Technology‘s Foresight Programme has recognised these
systems as a strategic technology for the future, having considerable potential for wealth creation
through the development of hitherto unknown products, and performance enhancement of existing
products in a broad range of industrial sectors.
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The concept of engineering materials and structures which respond to their environment,
including their human owners, is a somewhat alien concept. It is therefore not only important that
the technological and financial implications of these materials and structures are addressed, but
also issues associated with public understanding and acceptance.
The core of Yanagida‘s philosophy of ken materials is such a concept. This is ‗techno-
democracy‘ where the general public understand and ‗own‘ the technology. Techno-democracy
can come about only through education and exposure of the general public to these technologies.
However, such general acceptance of smart materials and structures may in fact be more difficult
than some of the technological hurdles associated with their development.
Military Applications:
Number of distinctly military applications for the use of smart materials and smart systems
can be delineated, among them:
Smart Skin : In battle soldiers could wear a T-shirt made of special tactile material that can detect
a variety of signals from the human body, such as detection of hits by bullets. It can then signal the
nature of the wound or injury, analyze their extent, decide on the urgency to react, and even takes
some action to stabilize the injury.
Smart Aircraft : Smart materials can be used in a few potential locations in the structures in
aircraft.
Autonomous Smart systems: Ground, marine or space smart vehicles will be a feature of future
battles. These carriage systems, whether manned or unmanned, and equipped with sensors,
actuators and sophisticated controls, will improve surveillance and target identification and
improve battlefield awareness.
Stealth Applications. The smart vehicles mentioned above could be constructed using stealth
technologies for their own protection: the B-2 stealth bomber or the F-117 stealth fighters are good
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69
examples of this technology. And, just as important, smart systems are needed for rapid and
reliable identification of space or underwater stealth targets. The identification and detection of
such targets, as well as the subsequent decision to take action with or without operator
intervention, is another potential application of smart systems.
The Potential Benefits:
The potential future benefits of smart materials, structures and systems are amazing in their
scope. This technology gives promise of optimum responses to highly complex problem areas by,
for example, providing early warning of the problems or adapting the response to cope with
unforeseen conditions, thus enhancing the survivability of the system and improving its life cycle.
Moreover, enhancements to many products could provide better control by minimizing distortion
and increasing precision. Another possible benefit is enhanced preventative maintenance of
systems and thus better performance of their functions. By its nature, the technology of smart
materials and structures is a highly interdisciplinary field, encompassing the basic sciences —
physics, chemistry, mechanics, computing and electronics — as well as the applied sciences and
engineering such as aeronautics and mechanical engineering. This may explain the slow progress
of the application of smart structures in engineering systems, even if the science of smart materials
is moving very fast.
CONCLUSION
The field of smart materials and structures is emerging rapidly with technological
innovations in engineering materials, sensors, actuators and image processing. Smartness describes
self-adaptability, self-sensing, memory, and multiple functionalities of the materials or structures.
These characteristics provide numerous possible applications for these materials and structures in
aerospace, manufacturing, civil infrastructure systems, and biomechanics. Self-adaptation
characteristics of smart structures are a great benefit that utilizes the embedded adaptation of smart
materials like shape memory alloys. By changing their properties, smart materials can detect faults
and cracks and therefore are useful as a diagnostic tool. This characteristic can be utilized to
activate the smart material embedded in the host material in a proper way to compensate for the
fault. This phenomenon is called self-repairing effect. The technologies using smart materials are
useful for both new and existing constructions. Of the many emerging technologies available the
few described here need further research to evolve the design guidelines of systems. Codes,
standards and practices are of crucial importance for the further development.
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Today, the most promising technologies for lifetime efficiency and improved reliability
include the use of smart materials and structures. Understanding and controlling the composition
and microstructure of any new materials are the ultimate objectives of research in this field, and is
crucial to the production of good smart materials. The insights gained by gathering data on the
behaviour of a material‘s crystal inner structure as it heats and cools, deforms and changes, will
speed the development of new materials for use in different applications. Structural ceramics,
superconducting wires and nanostructural materials are good examples of the complex materials
that will fashion nanotechnology. New or advanced materials to reduce weight, eliminate sound,
reflect more light, dampen vibration and handle more heat will lead to smart structures and
systems which will definitively enhance our quality of life.
REFERENCES
1. DuerigT.W, Melton K.N, Stoeckel D., Wayman C.M., Engineering aspects of shape memory
alloys, Butterwort heinemann Ltd:London,1990.
2. MauroDolce,D.Cardone and R.Marnetto, Implementation and Testing of Passive control
Devices based on Shape Memory Alloys, Earthquake engg. And structural
dynamics,2000;Vol-29, pp945-96
3. J.Holnicki-szulc and J.Rodellar(eds), Smart Structures.,3.High Technology-Vol.65
4. N. Krstulovic-Opara and A.E. Naaman, ACI Structural Journal, March-April 2000,
pp335-344
5. Hannant, D.J and Keer, J.G., Autogeneous Healing of Ti Based Sheets, Cement and
Concrete Research, V-13,1983
6. Sun, G. and Sun, C.T., Bending of Shape Memory Alloy Reinforced Composite Beam,
Journal of Materials Science, Vol-30, No.13, pp5750-5754.
7. Jones,R.T.,Sirkis.J.S.,andFriebele,E.J.(1997)Detection of impact location and
Magnitude for Isotropic plates Using Neural Networks, Journal of Intelligent material
systems and Structures,7,pp90-99.
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SEISMIC RESPONSE OF SIFCON STRUCTURAL ELEMENTS
Dr.G.S.THIRUGNANAM
Institute of Road and Transport Technology, Erode
ABSTRACT
There have been immense developments in the field of Civil Engineering in the last few
decades and the Civil Engineering in our country have kept pace with rapid advances made in
technology. One of the spectacular advances made in the field of Civil Engineering is the
production of high performance materials. Slurry infiltrated fibrous concrete (SIFCON) is one of
the high performance material. SIFCON is a special type of fibre reinforced cement composites
containing as much as 20% volume fraction of steel fibres. In conventional fibre reinforced
concrete, the fibre volume fraction is generally limited to 2 to 3%. Mixing and placing becomes
difficult because of balling effect, if the fibre volume exceeds 2%. Hence a different construction
technique was devised to increase the fibre volume fraction leading to the development of the
SIFCON. Because of its high fibre content SIFCON has unique properties in the areas of both
strength and ductility. Infiltrating steel fibre network with specially designed cement based slurry
makes SIFCON. The primary variables are fibre contents and matrix composition. The addition of
steel fibres to mortar leads to improvement in several properties of concrete.
The present investigation is taken up to assess the load carrying capacity, stiffness
degradation, ductility characteristic and energy absorption of structural elements such as beams,
slabs and wall panel elements of RC,FRC and SIFCON under cyclic loading. Based on
the present investigation significant conclusions are arrived which shows that the SIFCON
structural elements, such as beams, slabs and wall panels, behaves relatively better than
conventional concrete in all aspects.
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INTRODUCTION
SIFCON is slurry infiltrated high performance fibrous concrete which contains relatively
high volume percentage of steel fibres as compared to conventional steel fibre reinforced concrete.
It is different from conventional SFRC in terms of fabrication and composition. SIFCON is also
called as a high volume fibrous concrete. In conventional SFRC fibre volume fraction varies from
1-3 percent depending on the geometry of fibres and type of application where as in SIFCON it
varies from 4-20 percent.
SIFCON is produced by preplacing the steel fibres in a mould to its full capacity and later
infiltrating it through by cement based slurry. Once the slurry infiltration is completed, the curing
of SIFCON is same as that of the conventional concrete. More fibres can be incorporated if aspect
ratios are low. The volume fraction can be increased by using mild vibration.
One of the important aspects in the fabrication of SIFCON is fibre orientation. Fibres tend
to orient themselves in two dimensions. If fibres are long, two dimensional effects can be seen in
thick section.
The primary constituent materials of SIFCON are steel fibres and cement based slurry. The
slurry can contain cement, sand and additives or cement, fly ash, silica fume and additives. In this
cement slurry is prepared by mixing cement, fly ash, silica fume and additive with water. In most
cases high range water reducing admixtures are used in order to improve the flowability of slurry
without increasing the w/c ratio.
A large variety of fibres have been investigated for use in SIFCON. Steel fibres give better
result than that of the other types of fibres. In most applications fibres with hooked ends have
been used, the fibre length vary from 30mm-60mm. the length diameter ratio (aspect ratio) varies
from 60-100. Crimped and straight fibres have also been used in some applications. Past studies
have shown that using of crimped round steel fibres give better results than that of the other steel
fibres.
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The matrix in SIFCON has no coarse aggregate but having high cementitious content. It
contains fine sand, additives such as fly ash, micro silica and latex emulsions. In some cases
cement, fly ash and silica fume is used along with water reducing additive. The matrix fineness
must be designed so as to properly infiltrate the fibre network formed in the mould. Otherwise
large pores may form and leading to substantial reduction in properties. Additives such as high
range admixtures such as super plasticizer are used for improving the flowing characteristics of
SIFCON.
PROPERTIES OF SIFCON
1. Density
The unit weight of slurry used in SIFCON varies form 10 to 19 kN/m3
and that of the
SIFCON composites form 20 to 24 kN/m3
for steel fibre volume content of 5 percent, and from 31
to 34 kN/m3
for steel fibre volume content of 20 percent.
2. Drying Shrinkage
The ultimate drying shrinkage strain of SIFCON is only about 15 to 20 percent that of
unreinforced paste or mortar. It is apparent hat the mass of interconnected steel fibres has the
restraining effect on the shrinkage of the composite. Actual ultimate shrinkage strain for SIFCON
is in the range of only 0.02 to 0.04 percent.
3. Modulus of Elasticity
Recent investigations have shown that the elastic modulus of SIFCON is different for
tensile and compressive loading. The elastic modulus depends on a number of parameters which
include the matrix and fibre properties, the fibre reinforcing parameters which include the matrix
and fibre properties of the interface between the fibre and the matrix. For about the same volume
fraction of fibres, the modulus of SIFCON increases with the compressive strength of the
composite. However, the modulus is also quite sensitive to the length of the fibres or equivalently
to the bond at the fibre matrix interface. Accurate predictions of elastic modulus are becoming
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
74
increasingly important in studies related to damage mechanics, stiffness degradations, fracture
characteristics length and the like. Generally, the secant modulus of elasticity for SIFCON is in the
range form 17.5 to 24.5 X 103 N/mm
2.
4. Resistance to Impact and Blast Loading
Investigations conducted by a number of researchers indicate that SIFCON has a great
energy absorbing capacity under impact and blast loading. Its performance is also better than that
of reinforced concrete for missile loads.
5. Abrasion Resistance
SIFCON possesses very high abrasion resistance when compared with plain concrete and
SFRC specimens. The abrasion resistance improves with the increase in the percentage of fibres.
Mechanism and Mode of Failure
Crack occurs when composite strain exceeds the crushing strain of matrix. Since the
modulus of elasticity of the fibres is more than that of matrix, fibres deform less and exert a
pinching force at the crack tip. Cracks are prevented from propagating until the composite ultimate
stress is reached, when failure occurs either by simultaneous yielding of fibres and crushing of
concrete or by fibre matrix interfacial failure.
APPLICATIONS OF SIFCON
SIFCON is relatively a new product. The following are some of the successful
applications.
1. Security Vaults
In this application the product must have excellent resistance against torching, drilling and
chipping. Both reinforced concrete and steel have certain weakness. For instance steel walls can be
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
75
torched; where as the concrete walls can be drilled and blasted to gain entry. But SIFCON has an
advantage over the steel and concrete. SIFCON walls cannot be torched because concrete will
resist deterioration heat and will also slow down heat the conduction. The composite can resist
blast loading because of its ductility. The chipping and drilling is very hard because of the fibres
obstruction. Hence SIFCON is being used for various types of safe vaults and vault doors.
2. Explosive Resistant Containers
SIFCON has been used for making container to store various kinds of immunition. The
primary concern in this application is to limit the spread of explosions from container to
container. SIFCON provides good resistance in arms of containing the exploded materials in one
chamber. The primary weak points were found to be connections between the walls. Successful
connections have already been developed using the test results of prototype boxes. The SIFCON
is also used for resistance to explosive in missile silo structure.
3. Repair Materials for Structural Components
SIFCON serves as an excellent repair material because it is compatible with reinforced
concrete in terms of stiffness and dimensional changes caused by temperature. It can be placed in
hand to reach places and provides good bonding to the parent concrete because of the presence of
fibers. The matrix can be modified to suit the particular repair. For example rapid strength
required can be obtained using accelerators.
SIFCON was used to repair prestressed concrete beams spanning in an interstate highway
in the state of new Mexico. The beams had been damaged by a vehicle passing under the bridge.
Some of the pretensioned tendons had been exposed by the damage. The beams were restored
using SIFCON without removing them. Restoration in place not only resulted in a large cost
saving but also reduced the time of repair by few months. The repaired beam which is more than
eight years old is functioning well.
4. Bridge Rehabilitation
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SIFCON has been used for a number of bridge rehabilitation projects. Typically, the area to
be repaired is chipped off and cleaned thoroughly. The fibres are placed in position and infiltrated
with slurry. In most cases the infiltration is achieved by gravity alone.
5. Pavement Rehabilitation
Pavement rehabilitation is similar to bridge rehabilitation except that the repair surfaces are
normally large and the loading patterns is primarily compressive. In certain cases, a thin, bonded
overlay is placed on the existing surfaces to act as a wearing surface.
The construction sequence is the same as in bridge deck repairs. SIFCON has been
successfully used for overlays of varying thickness from 10 to 50mm.
6. Precast Product
Precast product made out of SIFCON slabs, safe vaults and special unit such as basketball
ground. Precast slabs that are 25 to 50mm thick were used primarily as the wear resistant surface.
The slabs which provide impact resistance have also been used in airport taxiways and gate areas.
7. Refractory Applications
The concept of SIFCON has also been successfully used for refractory application. In this
application, stainless steel fibres are used with calcium aluminates cement matrix. SIFCON was
found to perform well under the high temperature shock and mechanical loading. The service life
of components such as a soaking pit cover made using SIFCON was found to be much longer than
the components made with other material.
CASTING OF STRUCTURAL ELEMENTS
a) Beams:
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The steel mould of size 100 x 150 x 1100mm and the reinforcement of two numbers of
8mm diameter steel bars are provided in tension as well as in compression zone, with two legged
6mm diameter stirrups at 100mm centre to centre, is provided for casting all the beam specimens.
For RC beams, after placing the steel reinforcement in to steel mould with a cover of 25mm, the
prepared concrete, using the mix proportion, is poured in layers and vibration is given for each
layer. After 24 hours the beam specimen is demoulded from the steel mould and it is taken for
curing for 28 days. For FRC beams, after the preparation of the concrete, the steel fibres are
sprinkled in the concrete and the concrete is poured in to the mould after the placement of
reinforcement in to the mould and the remaining procedure is same as that of RC beam. For the
SIFCON beam ,after the placement of the reinforcement in to the steel mould the steel fibre
network is formed in to the mould to its full volume in such a way that the reinforcement should
be fully covered by the steel fibres.
Then the cement slurry prepared as per the mix proportion is slowly poured in to the mould
till the mould is completely filled with slurry and the vibration is provided to entrap the air
between steel fibres and the remaining procedure is same as that of RC beam.
b) Slabs and Wall Panels:
The steel mould of size 700 x 700 x 30mm steel mould and the reinforcement of 6mm
diameter bars provided on both directions with 70mm c/c spacing with edge distance of 20 mm on
all sides is used for casting, the remaining procedure is same as that of beams. For all the slabs and
wall panel‘s clear cover of 12 mm is provided.
TEST SETUP & TESTING OF SPECIMENS
Beam specimens of RC, FRC & SIFCON are placed as simply supported condition & the load is
applied at two points which are located at 1/3 of the beam. The load is applied through screw jack
gradually. The central deflection is noted down for each increment and decrement of load. The
beams are subjected to cyclic & reversed cyclic loading. The loading setup for beam is shown in
Fig.
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The
slab
specimens of RC, FRC & SIFCON are placed horizontally in simply supported condition on 2
sides as shown in the Fig. and the line load is applied with the help of the steel beam selection
through out the slab at right angle to the supports through screw jack and central deflection is
noted down using dial gauge. The slabs are subjected to cyclic loading only.
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The wall panel elements of RC, FRC & SIFCON are placed vertically in simply supported
condition on three sides as shown in the Fig. and the line load is applied gradually on the centre of
the slab through screw jack. For each load increment / decrement the corresponding central
deflection is noted down. In this case also the wall panels are subjected to cyclic loading only.
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BEHAVIOUR OF BEAMS:
Loading History of SIFCON Beam:
In this case totally 16 cycles were imposed, in these, 8 cycles were forward and 8 cycles
were for reversed loading. The ultimate load is observed as 50 KN. The load deflection curve is
shown in figure as below.
-60
-40
-20
0
20
40
60
-15 -10 -5 0 5 10
DEFLECTION(mm)
LO
AD
(KN
)
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The following table shows the experimental results of the SIFCON beam.
Cycle
Ultimate
load
(KN)
Central
deflection(
mm)
Ductility
factor
Cumulative
Ductility
factor
Stiffness
(KN/mm)
Energy
absorption
(KN/mm)
Cumulative
Energy
absorption
(KN/mm)
1F
1R
2F
2R
3F
3R
4F
4R
5F
5R
6F
6R
7F
7R
20
20
30
30
40
40
50
50
50
50
50
50
50
50
1.78
1.52
2.14
2.46
2.88
3.7
4.47
6.49
5.43
7.81
6.62
9.73
7.97
11.94
0.77
0.61
0.93
0.98
1.25
1.48
1.93
2.6
2.4
3.12
2.88
3.89
3.47
4.78
0.77
1.38
2.31
3.3
4.54
6.03
7.9
10.57
12.93
16.05
18.93
22.82
26.29
31.06
11.23
13.16
11.18
12.2
11.05
10.81
11
7.7
9.21
6.4
7.55
5.14
6.27
4.19
9.36
6.24
10.95
7.3
12.3
8.2
65.02
97.53
107.8
161.7
151.24
226.86
240.2
360.3
9.36
15.6
26.55
33.85
46.15
54.35
119.37
216.9
324.7
486.4
637.64
864.5
1104.7
1465
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0
10
20
30
40
50
60
RC FRC SIFCON
BEAM DESIGNATION
UL
TIM
AT
E L
OA
D(K
N)
8F
8R
50
50
6.12
13.79
2.66
5.5
33.73
39.24
5.8
3.6
240.4
360.6
1705.4
2066
COMPARISION OF THE TEST RESULTS
Load Carrying Capacity The ultimate load carrying capacity of the beams of RC, FRC and
SIFCON was observed as 31.5kN, 36kN and 50kN respectively. The load carrying capacity of the
beam SIFCON and FRC was nearly, 58.73% and 14.3% greater than RC beam respectively. It is
seen from the experimental investigation that of the ultimate load carrying capacity increases
considerably in SIFCON beams compared to RC and FRC beams. The ultimate load carrying
capacity of beams is
shown in fig
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Cumulative Ductility Characteristics
The ductility factor was 0.62 for the beam – RC during the first cycle, whereas for the
beam FRC and SIFCON was 0.88 and 0.77 respectively, during the final cycle of loading the
cumulative ductility factor was 17.96 for the RC beam, whereas it was 21.62 for beam FRC and
39.24for the beam SIFCON. The SIFCON and FRC beam specimens have higher ductility than the
other specimens. The ductility of SIFCON beam and FRC beam specimens was 2.18times and
1.21 times greater than the RC beams. The comparison of cumulative ductility factor is shown in
fig.
0
5
10
15
20
25
30
35
40
45
RC FRC SIFCON
BEAM DESIGNATION
CU
M. D
UC
TIL
ITY
FA
CT
OR
Cumulative Energy Absorption Capacity
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The relative energy absorption capacity of the beam RC, FRC and SIFCON were
16.65KN-mm, 17.55KN-mm and 15.6KN-mm respectively during the first cycle of loading. The
cumulative energy absorption of the beam RC, FRC and SIFCON were calculated as 579.7KN-
mm,
590.6KN-mm and 2066KN-mm respectively. The cumulative energy absorption of SIFCON and
FRC beams always higher than the RC beam, which is evidently shown in fig.
0
500
1000
1500
2000
2500
RC FRC SIFCON
BEAM DESIGNATION
CE
A(K
N/m
m)
The experimental results are tabulated as shown below
BEAM
DESIGNATION
ULTIMATE
LOAD(KN)
CUMULATIVE
DUCTILITY
FACTOR
CUMULATIVE
ENERGY
ABSORPTION
(KN-mm)
STIFFNESS
RANGE
(KN/mm)
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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RC 31.5 17.96 579.7 13.85-6.89
FRC 36 21.62 590.61 12.86-6.1
SIFCON 50 39.24 2066 11.232-3.6
SLAB
DESIGNATION
ULTIMATE
LOAD (KN)
CUMULATIVE
DUCTILITY
FACTOR
CUMULATIVE
ENERGY
ABSORPTION
(KN-mm)
STIFFNESS
RANGE
(KN/mm)
RC 12.8 13.19 43.68 2.19-1.44
FRC 14.4 17.86 84.28 1.26-1.05
SIFCON 16 23.43 123.88 2.58-0.92
CONCLUSIONS
Based on experimental study carried out on structural elements such as beams, slabs and wall
panels of RC, FRC and SIFCON, the following conclusions are drawn.
Beam SIFCON with RC Beam and FRC Beam
1. The load carrying capacity of SIFCON beam was increased by 1.59 times than that of RC
beam and 1.39 times greater than that of FRC beam.
2. The cumulative ductility of SIFCON beam was increased by 2.18 times greater than that of
RC beam and 1.81 times greater than that of FRC beam.
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3. The cumulative energy absorption capacity of the SIFCON beam was increased by 3.56
times greater than that of RC beam and 3.49 times greater than that of FRC beam.
SIFCON Slab with RC Slab and FRC Slab
1. The load carrying capacity of SIFCON slab was increased by 1.25 times greater than that
of RC slab and 1.11 times greater than that of FRC slab.
2. The cumulative ductility of SIFCON slab was increased by 1.77 times greater than that of
RC slab and 1.31 times greater than that of FRC slab.
3. The cumulative energy capacity of SIFCON slab was increased by 2.83 times greater than
that of RC slab and 1.47 times greater than that of FRC slab.
SIFCON Wall Panel with RC Wall Panel and FRC Wall Panel
1. The ultimate Load Carrying Capacity of SIFCON is increased by 4.5 times greater than
that of RC 3.4 times greater than that of FRC wall panel.
2. The cumulative ductility factor of SIFCON wall panel is increased by 2.13 times greater
than that of RC and 1.83 times greater than that of FRC wall panel.
3. The cumulative energy absorption of SIFCON wall panel is increased by 27.23 times
greater than that of RC wall panel and 26.38 times greater than that of FRC wall panel.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
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STUDY ON FIBRE REINFORCED CEMENTITIOUS COMPOSITES
Dr.A.JAGANNATHAN
Assistant Professor in Civil Engineering,
Pondicherry Engineering College,
Pillaichavady, Puducherry – 605 014
E- mail: [email protected]
ABSTRACT
Even though fibre was used from the ancient days, but its awareness and utilization is
growing in the recent decade. In this study a low modulus synthetic fibre called Polyolefin fibre
and both end hooked Steel fibre was used. In the first phase, engineering properties such as
compressive strength, split tensile strength and flexural strength was found using both fibre
varying 0% – 2% by volume of the specimen. In green state workability test was also found. The
engineering properties of cementitious composites increased with increase in fibre content. This
contribution was found significant in 1.5% and above. However steel fibre has got higher value
than that of polyolefin fibre. In the second phase flexural strength study was made on specially
cast slab specimen in a specially fabricated load frame at four points loading. Here also it is seen
that flexure strength of slab specimen increased with increase in % of fibre content and it is
appreciable @1.5% and above.
INTRODUCTION
Brittleness is the inherent property of cementitious composites due to its low tensile
strength and poor fracture strain properties. Cementitious composites are used for all construction
finishing‘s, grouting, lining and thin element casting. Apart from all, Cementitious composites is
the base media for concrete. Hence it should be strong, possess good deformation characteristics,
impact and fatique resistance. The above said characteristic could be generated by the use of fibre.
Fibres are the discrete and discontinuous type of reinforcement which is used to reinforce the
brittle composites from the ancient days [1, 2].
Asbestos fibre was popularly used but its application is slowly reduced due to its hazard
risk factors [3-5].At present steel, glass, carbon and synthetic (Polymeric) fibre are commercially
available which are essential to use in construction industry due its unique behavior and
contribution. The mechanical properties of cementitious composites by the fibre depends on
geometric configuration such as type of fibre, length – to – diameter ratio (aspect ratio ),the
amount of fibre ,size, shape, elastic properties, strength properties, method of preparation etc[6].
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The interest on use of fibre in cementitious composites is to improve ductility behaviour by
the way of bridging crack i.e. by improving cracking strain. During the service period the
formation of micro crack is delayed by the micro type of fibre i.e. post cracking zone [7,8].In the
cracking mechanism high modulus of composites and good bond character‘s of fibre are excellent
in resisting pre cracking zone where as low modulus fibre are effective in post cracking zone
[9,10].
In this investigation the high modulus hooked end steel fibre and low modulus polyolefin
synthetic fibre were combined in various proportions by volume of specimen. In this paper
engineering properties as well as flexural strength properties under four point loads were studied in
specially fabricated flexure set up.
EXPERIMENTAL INVESTIGATION
Materials
In this study, 43 grade OPC was used. The cement was tested as per BIS procedure and the
test results were satisfied the requirements of IS: 8112-1989. Locally available river sand passing
through 2.36mm sieve was used. The fine aggregate was tested in accordance with IS: 2386-
1963.The test results conformed that the sand used was Grading Zone II and specific gravity was
2.32 as per IS: 383-1970. The macro synthetic fibre named Polyolefin and both end hooked steel
fibre were used for this study. The physical properties obtained from the concerns are presented in
Table1& Table 2.
Mix Details
The cement mortar proportion was fixed having sand cement ratio of 3 by weight and water
cement ratio of 0.43. The water cement ratio decided here is the average value recommended for
ferrocement application. This water cement ratio satisfies a slump value of 50 mm stipulated in
ACI: 549[11] and Ferrocement Model Code (FMC)[12]. The workability performance of cement
mortar with and without fibre was found using mortar flow table test as recommended in IS 2250-
1981[13]. The flow value of the mortar was experimented only for worst condition i.e. 2% of
polyolefin and 2% steel. The percentage of flow value obtained is presented in Table 3.
Casting
To study engineering properties 100 mm cube mould, 100mm dia & 200mm height
cylinder and 40x40x160mm square prism were cast. In the next stage flexural slab specimen
700x150x15mm size were cast. In the cementitious composites fibre content was varied from 0-
2% by volume. After making through mix of all the ingredients of matrix, the selected weight of
fibre were added and mixed to get uniform distribution of fibre. In the prepared flexure slab
specimen mould the wet fibre composites was spread in two layers, leveled and compacted using
float and straight edge. The specimen were removed after 24 hours and cured normally under
water.
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Testing
The cube, cylinder and prism specimen were tested at the end of 28 days curing period as
per BIS recommendations [14-16]. The flexure specimen was surface dried, white washed on both
sides to aid visibility of formation and propagation of crack. Then the centre line and loading line
@20cm apart were marked to keep and test in specially fabricated loading frame. The testing setup
is shown in Fig.1.Deflection at centre of the panel was recorded using LVDT for every five
divisions in the proving ring dial gauge (capacity 10 KN).The schematic diagram of loading is
shown in Fig.2.
RESULTS AND DISCUSSION
Strength Properties
The strength properties cementitious composites of individual fibre are presented in Table
4.The individual fibre cementitious composites strength properties have got significant
improvement for the fibre content 1.5% and above. But in case of steel fibre, this contribution is
found more than polyolefin fibre. This may be due to the good bonding of steel fibre with
cementitious composites and hooked end might have assisted against pullout and crack. In split
tensile strength, fibre contribution was found to be most effective in both fibrous mortars. This
contribution is increased with increase in percentage of fibre. Fibre contribution eradicates the
configuration (i.e. ‗the split tensile strength is 10% of cube compressive strength‘).The
performance of strength properties of fibre reinforced cementitious composites is shown in Figs.3-
5.
Flexural Strength
Flexural strength of cementitious composites reinforced with polyolefin and steel fibre is
presented in Table 5. From the test results in an overall observation it is seen that the addition of
fiber 1.5% and above gained significant strength in flexure compared to reference matrix strength.
Cementitious composites with polyolefin fiber 1.5% and 2% gained strength about 34% and 60%
respectively compared to reference matrix. Similar trend is also seen in Cementitious matrix with
steel fiber but the trend of increase is more than 100% in 1.5% and 2% fiber content by volume.
There is no marginal improvement when increasing the fiber content. The crack width is found to
be almost same 0.1mm. The load- deflection diagram Figs 6-7 gives the linear variation up to
breaking point since failure occurred was brittle failure. Flexural strength of cementitious
composites reinforced with polyolefin and steel fibre depicted in the form of bar chart and shown
in Fig.8.Tested flexure slab specimen was photographed to study crack and failure pattern which
presented in Figs. 8-10.
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CONCLUCTIONS
Based on the present experimental study the following conclusions are drawn:
1. The workability performance of cementitious composites decreases with increase in fibre
content.
2. Addition of fibre contributed for the engineering properties. This contribution is found
significant for the fibre content 1.5% and above.
3. The improvement in split tensile and flexure strength will enhance ductility under bending
and toughness in both flexure and impact.
4. Flexural load increased with increase in fibre content in both fibre. But steel fibre gained
flexural strength even more than100% in 1.5% fibre content.
5. Enhanced characteristics of cementitious composites can be used for retrofitting,
renovating old and deteriorated structural elements apart from regular applications like
canal, tunnel lining, roofing, grouting etc.
REFERENCES
1. Dr.Prakash, K.B., Ravi, K., and Nataraj, K.C., ―Characteristics properties of Hybrid fiber
Reinforced Concrete produced with Fibers of different Aspect Ratios‖, Construction
Engineering & Construction Review, Dec-2006, pp 50-60.
2. Zongcai Deng., and Jianhvi Li., ―Mechanical behavior of concrete combined with steel
and synthetic macro-fibers‖, International Journal of physical sciences, Vol.2, Oct.2006, pp 57-66.
3. PitiSukontasukkul., ―Tensile Behavior of high content steel and polypropylene fiber
reinforced Mortar‖, Thammasat International Journal science on Tech, Vol.8, No.3, July-Sep
2003, pp 50-56.
4. ACI Committee 549,2R-04 ―Report on Thin Reinforced Cementitious Products‖,
Farmington Hills, Michigan.
5. ACI 544 ―State – of- the – Art Report on Fiber Reinforced Concrete‖.
6. ACI 544.4R ―Design Considerations for Steel Fiber Reinforced Concrete‖.
7. Parviz Soroushian., and Atif Tlili., et al ―Development and characterization of Hybrid
Polyethylene fibers Reinforced cement composites‖, ACI Materials Journal, V.90, No.2, March-
April.1993, pp 182-190.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
91
8. John S. Lawler., Daide Zampini., and Surendra P. Shah., ―Permeability of Cracked Hybrid
Fiber – Reinforced Mortar under Load‖, ACI Materials Journal, V.99, No.4, July-August 2002, pp.
379-384.
9. Pons, G., Mouret, M., Alcastara, M., and Granju, J.L., ―Mechanical behavior of self
compacting concrete with hybrid fibre reinforcement‖, Materials and Structures, Vol. 40,
Aug.2007, pp 201-210.
10. Piti Sukontasukkul., ―Toughness Evaluation of Steel (SFRC) and Polypropylene fiber
Reinforced Concrete (PFRC) Beams under Bending‖, Thammasat International Journal science on
Tech, V.9, No.3, July-Sep 2004, pp 35-40.
11. ACI Committee Report, 549 R-97, ―Guide for the Design, Construction, and Repair of
Ferro Cement‖, IR-88, ACI Structural Journal, May-June, pp 325-351.
12. Ferrocement Model Code (FMC), Building Code Recommendations for Ferrocement (IFC
10-01) Reported by IFS Committee 10, Asian Institute of Technology, IFIC, Thailand, January
2001.
13. IS: 2250-1981, ―Code of Practice for Preparation and Use of Masonry Mortar‖, Bureau of
Indian Standard, New Delhi.
14. IS: 9013-1978, ―Method of Making, Curing and Determining Compressive Strength Cured
Concrete Specimen‖, Bureau of Indian Standard, New Delhi.
15. IS: 5816-1959, ―Method of Test for Split Tensile Strength of Concrete (First Revision)‖,
Bureau of Indian Standard, New Delhi.
16. IS: 4031(Part8)-1968, ―Methods of Physical Test for Hydraulic Cement: Determination of
Transverse and Compressive Strength of Plastic Mortar Using Prism‖, Bureau of Indian Standard,
New Delhi.
Table 1 Physical Properties of Polyolefin Fibre
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92
Sl.
No. Characteristics Properties
1 Base resin Polyolefin
2 Length 48mm
3 Shape
Straight
4 Surface Texture Continuously embossed
4 Tensile Strength 550 MPa
5 No. fibers per kg 35,000
6 Specific Gravity 0.91
7 Young‘s Modulus 6 GPa
8 Melting Point 150◦ - 165
◦ C
9 Ignition Point Greater than 450◦ C
Table 2 Physical Properties of Steel Fibre
Sl.
No. Characteristics Properties
1 Length 30 mm
2 Average Diameter 0.5 mm
3 Aspect Ratio 60
4 Density 7850 kg/m3
5 Young‘s Modulus 210 Gpa
Shape Straight and hooked end
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6
7 Tensile Strength 530 MPa
Table 3 Flow Value of Cement Mortar
Sl.
No.
Fibre Content
Flow Value
(%)
1 Reference- 0% 19.75
2 Polyolefin fibre 2% 9.75
3 Steel fibre2% 6.75
Table 4 Strength Properties of Fibre Reinforced Cementitious Composites
Type of Fibre Compressive
Strength
(N/mm2 )
Split Tensile
Strength
(N/mm2 )
Flexural
Strength
(N/mm2 )
Polyolefin
(%)
Steel
(%)
0.0 0.0 22.09 3.06 5.56
0.5 - 22.45 3.31 5.62
1.0 - 29.03 3.36 5.76
1.5 - 32.89 3.75 5.93
2.0 - 33.50 3.85 6.31
2.5 0.5 30.45 3.58 5.65
3.0 1.0 35.90 4.43 6.35
3.5 1.5 39.06 5.28 6.87
4.0 2.0 39.74 6.16 7.19
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Table 5 Flexural Strength of Cementitious Composites Reinforced with
Polyolefin and Steel Fibre
Type of Fibre Flexural
Load
(N)
Maximum
Deflection
(mm)
Flexural
Strength
(N/mm2)
Crack
Width
(mm) Polyolefin
(%)
Steel
(%)
0 161 0.49 4.29 -
0.5 179 0.64 4.77 0.2
1.0 193 0.70 5.15 0.2
1.5 215 0.77 5.73 0.1
2.0 258 1.04 6.88 0.1
2.5 0.5 258 0.75 6.88 0.2
3.0 1.0 301 0.89 8.02 0.1
3.5 1.5 330 1.31 8.80 0.1
4.0 2.0 365 1.48 9.73 0.1
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Fig.1 Flexural Test Setup
Fig.2 Flexural Test loading Schematic Diagram
0
10
20
30
40
50
0 0.5 1 1.5 2 2.5
Fibre Content (%)
Co
mp
res
siv
e
Str
en
gth
(M
Pa
)
Polyolefin Fibre
Steel Fibre
Fig. 3 Compressive Strength of Cementitious Composites
P/2 P
P/2 P/2
Test Specimen
200 mm 200mm 200mm
600mm
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0
1
2
3
4
5
6
7
0 0.5 1 1.5 2 2.5
Fibre Content (%)
Sp
lit
Ten
sil
e S
tren
gth
(MP
a)
Polyolefin Fibre
Steel Fibre
Fig. 4 Split Tensile Strength of Cementitious Composites
012345678
0 0.5 1 1.5 2 2.5
Fibre Content (%)
Fle
xu
ral S
tren
gth
(M
Pa)
Polyolefin Fibre
Steel Fibre
Fig. 5 Flexural Strength of Cementitious Composites
0
0.05
0.1
0.15
0.2
0.25
0.3
0 0.5 1 1.5 2
Fiber Content (%)
Lo
ad
(K
N)
Reference
P - 0.5%
P - 1%
P - 1.5%
P - 2%
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Fig 6 Load-Deflection Behavior of Cementitious Composites Reinforced with Polyolefin
Fiber
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0 0.5 1 1.5 2
Fiber Content (%)
Lo
ad
(K
N)
S - 0.5%
S - 1%
S - 1.5%
S - 2%
Reference
Fig 7 Load-Deflection Behavior of Cementitious Composites Reinforced with Steel Fiber
0
2
4
6
8
10
12
0 0.5 1 1.5 2
Fibre Content (%)
Fle
xu
re S
tren
gth
(M
Pa)
Reference
Polyolefin Fibre
Steel Fibre
Fig. 8 Flexural Strength of Cementitious composites Reinforced with Fibres
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Fig.8 Flexural Test Specimen (Reference)
Fig. 9 Flexural Test Specimen - Polyolefin Fibre (0.5%-2%)
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Fig. 10 Flexural Test Specimen- Steel Fibre (0.5%-2%)
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PERFORMANCE OF CONCRETE ONE WAY SLABS REINFORCED
WITH NON METALLIC REINFORCEMENTS UNDER CONSTANT AND
VARIABLE REPEATED FATIGUE LOADING
Dr.R.Sivagamasundari*1
, Dr.G.Kumaran2
*1 Senior grade Lecturer, Structural Engineering, Annamalai University, Annamalai nagar, 600
002, Tamilnadu, India.
E-mail: [email protected]
2Professor of Structural Engineering, Annamalai University , Annamalai nagar, 600 002,
Tamilnadu, India.
E-mail: [email protected]
ABSTRACT
The environmental attack is relentless and sooner or later the alkaline properties of the
concrete cover are reduced leading to corrosion and spalling of concrete. Replacement of steel
reinforcements by the composite reinforcements is considered to be a more innovative approach.
Glass Fibre Reinforced Polymer reinforcements (GFRP) are viable alternate to the conventional
steel reinforcements owing to their excellent properties such as non-corrosive, nonconductive and
nonmagnetic properties. This study focuses mainly on the experimental studies on the behaviour of
GFRP reinforced concrete one way slabs under static, constant and variable amplitude repeated
loadings and it is compared with steel reinforced concrete one way slabs. A total number of
twenty one one- way concrete slabs are cast, out of which three are reinforced with conventional
steel reinforcements and nineteen are reinforced with Glass Fibre Reinforced Polymer (GFRP)
reinforcements. Among the twenty one slabs, seven are subjected to static loading, seven are
subjected to constant amplitude fatigue loading and seven are subjected to variable amplitude
fatigue loading. Finite element analysis is also carried out to study the effect of different
parameters on the flexural capacity of one way slabs. Different parameters like thickness of slabs,
reinforcement ratios, types of reinforcements and grades of concrete are considered. Based on this
study, the fatigue performance of the steel and GFRP reinforced concrete one way slabs are
compared.
Keywords: One way slabs, Glass Fibre Reinforced Polymer reinforcements (GFRP), Static
loading, Constant and Variable amplitude fatigue loading.
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INTRODUCTION
Glass Fibre Reinforced Polymer (GFRP) reinforcements are an alternative to epoxy coated,
galvanized or stainless steel reinforcements in any concrete member susceptible to corrosion by
chloride ion or chemical corrosion. GFRP reinforcements offer many advantages over steel
reinforcements including impervious to chloride ion and chemical attack, 1/4th weight of steel
reinforcement, transparent to magnetic fields and radio frequencies, easy in fabrication and
electromagnetic insulating properties.®. The use of GFRP reinforcements, in lieu of conventional
steel reinforcements requires better understanding under different loading conditions. Considerable
research has also been carried out mainly on FRP reinforced concrete specimens under
monotonically increasing load (1-6). Only a limited research has been carried out on FRP
reinforced concrete specimens under pulsating or repeated loading conditions. Therefore the
present study deals mainly with the flexural behaviour of Reinforced Concrete (RC) one way slabs
reinforced internally with GFRP reinforcements under both static and repeated loading conditions
(Constant and Variable amplitudes). Fatigue is defined as the degradation of a material as a result
of repeated applications of a large number of loading cycles. In the present study, two types of
repeated loading schemes such as Constant amplitude of repeated loading (scheme I) and Variable
amplitude of repeated loading (scheme II) are adopted.
EXPERIMENTAL PROGRAM
The experimental program consisted of twenty one one-way slabs of length 2400 mm and
600 mm width. The constructed slabs were divided into three categories with seven slabs in each
category. First category of slabs were simply supported and subjected to two point static loading.
A clear span of 2200mm was adopted between the supports. The load was applied using a 50 tones
capacity hydraulic jack and 50 tones proving ring and distributed at two points on the slab. The
load was given in increments of 2 KN at each stage of loading. The slabs were kept on the loading
frame and were instrumented with a linear variable differential transformer (LVDT range 0-
100mm) at mid span to monitor deflection. LVDTs of range 0-75mm were used to monitor
deflections at right and left loading points of the slab. Demec gauge (Demouldable mechanical
gauge) pellets were pasted at the topmost compression fibre axis, at the middle axis and at the
level of reinforcements of slab to note down the strains. Crack widths were measured using crack
detection microscope. The experimental setup of static loading is shown in Fig 1.The results of
static test of slabs are presented in Table.1.
Second category of slabs was subjected to constant amplitude of fatigue loading scheme.
By applying constant amplitude loading scheme, the slabs were subjected to sinusoidal wave form
fatigue load cycles between a minimum load level and a maximum load level. Fig.2 shows the
pattern of fatigue loading applied on the slabs. Prior to start the fatigue loading, the slabs were pre
cracked by applying smaller magnitude of static loading to observe the first crack load and initial
propagation of the cracks. After that the minimum load level was set at 10% of ultimate static load
of 1112 DGM slab to prevent any impact effect due to repeated loading and also to represent the
effect of superimposed loads on a bridge like pavement. The maximum load level was set at 80%
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of ultimate static load of 1112 DGM reinforced slab and applied uniformly at a rate of 4 Hz till the
failure of the slab. This procedure was followed up for all the slabs. The fatigue loading range was
chosen to be approximately symmetrical around the service load. Therefore the upper limit
simulates some kind of overloading on the specimen to enable the failure of the slab within a
reasonable time.
Table.1. Experimental and Theoretical results (Static loading condition)
SL
NO
Specification of
the slab specimens
Theoretical,
kN
Experimental,
kN
theo
mm
exp
mm
monocrw mm
crP
uP
crP
uP
1 1112 DGM 11.4 33 11.5 40 67.8 70.2 1.2
2 1122 DGM 11.4 43.6 12 55.2 61 59.2 0.9
3 1222 DGM 11.6 52 12.2 58.6 62.4 56.8 0.74
4 1322 DGM 12.0 56.2 12.6 65.4 62.2 52.4 0.7
5 1123 DGM 11.6 49.2 12.8 60.2 56.5 54.6 0.8
6 2122 DGM 19 62.5 22.6 73.5 40.2 45.6 0.42
7 112 DSM 11 30.4 11.5 40 30.4 40.8 0.36
M2, M3 Grades of concrete M20, M30 respectively; G1, G2, SGrooved, Sand coated GFRP
and Steel reinforcements; 1,2&,3 Different reinforcement ratios 0.65%, 0.82% & 1.15%
respectively; D1 and D2Thickness of slabs
For example, Designation of the slab:
1112 DGM 2M grade of concrete M20; 1G Grooved type GFRP reinforcement
1 Reinforcement ratio, 0.65%; 1D thickness of slab, 100 mm
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A 20mm thick neoprene sheet was used between the steel plate and the concrete surface to
avoid stress concentration. A 50KN capacity with 250mm stroke cyclic load tester controlled by
computer was programmed to apply the repeated loading on the slab. A deflectometer was used to
examine the residual deflection at mid point of slab specimen after every 1000 number of cycles.
The results of slabs under constant amplitude of fatigue loading are presented in Table.2. Fig.3.
shows the experimental test set up for repeated fatigue loading. Fig.4 is the Bar chart showing the
number of load cycles applied on the various types of slabs till failure of the slabs.
Table.2. Fatigue test results of the slabs (constant amplitude repeated loading)
Sl
no
Designation
of slabs
Number of load
cycles )( faticrw mm
Residual
deflection,
mm
P2/P1
1 1112 DGM 65,120 1.8 52 0.8
2 1122 DGM 93,260 1.2 42.6 0.58
3 1222 DGM 1,50,000 1.0 40 0.55
4 1322 DGM 3,02,210 0.74 36 0.49
5 1123 DGM 1,25,260 0.92 35.6 0.53
6 2122 DGM 4,00,000 0.5 20.6 0.44
7 112 DSM 67,510 0.4 35.2 0.8
P1= Ultimate static load of 1112 DGM
P2=Ultimate static load of all the slabs
Third category of slabs were subjected to variable amplitude of fatigue loading scheme by
selecting 2 KN as minimum load for all the slabs and different percentages like 20%, 40%, 60%,
and 80% of the static ultimate loads of the slabs were selected as maximum loads to access the
effect of cycling at lower peak load levels. Each fatigue loading step consisted of minimum load of
2KN to a specified percentage of ultimate load. Each and every fatigue loading steps was applied
for 10,000 cycles at a frequency of 4 Hz till failure of the slab occurs. The degree of fatigue
damage can be evaluated by the magnitudes of strains in reinforcement, crack width, elastic
deflection and residual (plastic) deflection. The deflections, crack widths, crack propagation, crack
patterns, modes of failure and number of cycles up to failure were measured during the repeated
loading at the end of each repeated loading step. The results of slabs under variable amplitude of
fatigue loading are presented in Tables.3 and 4.
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ANALYTICAL STUDY
I In this study, a non-linear finite element model representing a full size one-way concrete
slab is considered. Material modelling for concrete is done based on the compressive and tensile
behaviour and the degradation properties of concrete due to cracking and crushing using shell
elements (7, 8). GFRP reinforcements are modelled as layers which exhibit uni-axial response.
Table. 3. Crack widths (Variable amplitude repeated loading)
Sl
No
Designation of
slabs
Crack widths at various load
levels, mm )( faticrw at
Service
load
mm 0.2P 0.4P 0.6P 0.8P
1 1112 DGM 0.24 0.5 2 - 0.52
2 1122 DGM 0.18 0.36 1.02 1.6 0.42
3 1222 DGM 0.16 0.32 1.0 1 0.36
4 1322 DGM 0.12 0.28 0.8 0.8 0.32
5 1123 DGM 0.15 0.32 1.2 1.56 0.4
6 2122 DGM 0.08 0.26 0.5 0.84 0.26
7 112 DSM 0.06 0.18 0.44 - 0.24
Table.4. Deflections (Variable amplitude repeated loading)
Sl
No
Designation of
slabs
Deflections at various load levels, mm
0.2P 0.4P 0.6P 0.8P
1 1112 DGM 15.2 41.2 75.6 -
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2 1122 DGM 11.2 34.2 54.2 66.5
3 1222 DGM 10.6 32 52.6 64.2
4 1322 DGM 9.5 30.8 50.3 63.6
5 1123 DGM 10.5 32.4 52.6 62.4
6 2122 DGM 5.2 20.3 29.2 46
7 112 DSM 10.4 26 45.8 -
P=Static Ultimate load of the corresponding slabs
RESULTS AND DISCUSSION
Under static loading condition the ultimate load carrying capacity of 1122 DGM slab were
40% greater as compared to 1112 DGM and 112 DSM slabs. The ultimate deflection of 1122 DGM
was observed as 0.75 times smaller than 1112 DGM and 2.5 times greater than 112 DSM .Lesser
amount of deflections and smaller crack widths were observed in sand coated GFRP slabs than the
grooved GFRP slabs . This might be attributed by the good bonding effect existing between the
reinforcements and concrete .By increasing the reinforcement ratio, grade of concrete and the
thickness of the slabs, the maximum load carrying capacity of the slabs increases and the
corresponding deflection decreases. When the reinforcement ratio of sand coated GFRP reinforced
slabs was increased from 0.65% to 1.15%, the ultimate load carrying capacity increases from 6%
to 20% and rapid changes were not perceived in the corresponding deflections. The increase in the
thickness of the sand coated GFRP slabs, improved the static load carrying capacity by 35%, and
lowered the corresponding deflection by 0.7 times . On increasing the grade of concrete from 20
N/mm2 to30 N/mm2 for the sand coated GFRP reinforced slabs, 10 % improvement in the
ultimate load carrying capacity and an insignificant change in deflection (i.e., the stiffness of the
slabs did not change much when the concrete strength increases by 10 N/mm2) were observed.
Based on repeated cyclic loading results, it was observed that with the increase in the number of
load cycles, the corresponding ultimate deflection, number of cracks and the width of the cracks
increase. The slab 1122 DGM showed 1.43 times and 1.38 times greater fatigue performance than
1112 DGM and 112 DSM slabs respectively. The fatigue performance of 2122 DGM slab was
observed as 4.3 times higher than 1122 DGM slab. Also, by increasing the grade of concrete from
20 N/mm2 to 30 N/mm2, the fatigue performance of 1122 DGM was increased by 1.34 times. The
fatigue capacity of 1122 DGM exceeded the fatigue capacities of 1222 DGM and 1322 DGM by 1.6
and 3.24 times respectively. It was also noted that the magnitude of damage accumulated to the
slab reinforced with steel reinforcements is higher than GFRP reinforced slabs (9, 10, and 11).
Among all the GFRP reinforced slabs, sand coated GFRP reinforced slabs exhibited the lowest
residual deflection and the greatest stiffness. This was mainly attributed due to the closer values of
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106
the module of elasticity for GFRP reinforcements and concrete in addition to the linear-elastic
behaviour of GFRP reinforcements. Sand coated GFRP reinforced slabs proved an excellent
fatigue performance over the slabs reinforced with other types of reinforcements. It has been
observed that at the same load level, the deflection under cyclic loading is always greater than the
deflection under static loading. On increasing the number of load cycles, the stiffness of the slab
decreases and the increasing residual and elastic deflections confers the peak load level.
CONCLUSIONS
Experiments carried out on twenty one numbers of one-way concrete slabs, (out of which
three are reinforced with conventional steel reinforcements and eighteen are reinforced with GFRP
reinforcements) were studied. A rigorous analytical and experimental studies on the behaviour of
conventional and GFRP reinforced concrete one way slab under static and repeated loading were
investigated by considering reinforcement ratios, grade of concrete, thickness of slab and type of
GFRP reinforcements(with constant and variable amplitude loadings). All the slabs experienced
flexural type of failure. At ultimate load, GFRP reinforced slabs experienced concrete crushing
followed by the rupture of GFRP reinforcements. Sand coated GFRP reinforcements showed the
better fatigue performance than the grooved GFRP reinforcements due to their higher bonding
characteristics. Due to the low modulus of elasticity and different bond characteristics of the
GFRP reinforcements, slabs reinforced with GFRP reinforcements exhibited larger deflections and
strains than those reinforced with conventional steel reinforcements. Sand coated reinforced GFRP
slabs experienced 1.6 times greater fatigue life than that of conventional slabs. The fatigue
performance of grooved GFRP reinforced slabs was similar to that of conventional slabs. Based on
this study, it was found that a good agreement exists between the theoretical and experimental
results.
ACKNOWLEDGEMENT:
The authors wish to thank the University Grants Commission (UGC) of India for the
valuable financial support rendered from the UGC Major Research Scheme. The financial Grants
released for the project titled ―Alternative Reinforcements for Concrete Application‖ is greatly
appreciated.
REFERENCES:
1. ACI Committee 440 R (1996), ―State-Of-The-Art Report on Fiber Reinforced Plastic (FRP)
reinforcements for concrete structures‖.
2.Amnon Katz(2000), ―Bond to concrete of FRP Rebars after Cyclic loading‖, Journal of
composites for construction, vol.4 , No. 3, pp 137-144.
3.Benmokrane. B. ,O.Challal and R.Masmoudi(1995), ―Flexural response of concrete beams
reinforced with FRP reinforcing bars‖ ACI Materials Journals, Vol. 91, No.2.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
107
4.Craig R.Michaluk, Sami H.Rizkalla, Gamil Tadros and Brahim Benmokrane (1998) ―Flexural
behavior of one-way concrete slabs reinforced by Fibre reinforced plastic reinforcements‖, ACI
Structural Journals vol 95, No.3, pp 353-364.
5.Michale Theriault and Brahim Benmokrane (1998), ―Effects of FRP reinforcement ratio and
concrete strength on flexural behavior of concrete beams‖ Journal of composites for construction
vol.2, No.1,pp 7-16,1998.
6.Ombres.L.T., Alkhrdaji, and A.Nanni(2000), ―Flexural analysis of one way concrete slabs
reinforced with GFRP rebars‖, International meeting on composite materials, PLAST
2000,Proceedings,Advancing with composites 2000,Italy,May 9-11, pp.243-250.
7.Ferreira .A.J.M., P.P.camanho, Marques, A.T. Fenandes, A.A (2001), ―Modelling of concrete
beams reinforce with FRP rebars,‖ Journal of composite structures, 53, 107-116.
8.Kumaran G., D. Menon, and K. Krishnan Nair(2002), ―Evaluation of dynamic load on railtrack
sleepers based on vehicle-track modelling and analysis‖, International Journal of Structural
Stability & Dynamics, Vol. 2, No.3, pp. 355-374.
9.Kae-Hwan Kwak and Jong-Gun Park(2001), ―Shear-fatigue behavior of high-strength reinforced
concrete beams under repeated loading‖, Journal of Structural engineering and Mechanics, Vol 2,
No.3 .
10.Amir El-Ragaby, Ehab El-Salkawy and Brahim Benmokrane(2007), ―Fatigue analysis of
Concrete Bridge Deck Slabs reinforced with E-Glass/Vinyl Ester FRP Reinforcing bars,‖ Journal
of composite structures, vol.11,No.3,258-268.
11.Sobhy Masoud,Khaled Soudki and Tim Topper(2001),―CFRP strengthened and corroded RC
beams under Monotonic and Fatigue Loads‖, Journal of composites for construction, vol.5, No. 4,
pp 228-235.
0
25
50
75
100
0 50 100
Number of load cycles in thousands
Def
lect
ion,m
m
M2G2p1D1
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
108
Fig.1.Experimental setup for testing Fig.2.Constant amplitude fatigue loading
the Slabs
0
100
200
300
400
500
1 2
Various parametric Slabs
Num
ber
of
load
cycl
es i
n th
ousa
nds
M2G1p1D1
M2G2p1D1
M2G2p2D1
M2G2p3D1
M3G2p1D1
M2G2p1D2
M2Sp1D1
Fig. 3. Experimental setup for repeated Fig.4.Comparison of slabs-constant
loading
amplitude loading
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
109
USE OF SAWDUST ASH IN CONCRETE AS PART REPLACEMENT OF
SAND
M. Mageswari*1
, Dr.B.Vidivelli2
*1Research Scholar, Structural Engineering, Annamalai University, Annamalai nagar, 600 002,
Tamilnadu, India.
E-mail: [email protected] 2Professor of Structural Engineering, Annamalai University, Annamalai nagar, 600 002,
Tamilnadu, India.
E-mail: [email protected]
ABSTRACT
Concrete is the most widely used construction material in the recent years. Concrete
strength is influence by the quality of sand, coarse aggregate and cement. The challenge of the
civil engineering community in future will be to execute projects in harmony with the nature using
the concept for sustainable development involving the use of high performance, economic friendly
materials produce at free of cost with the lowest possible environment impact. In the context of the
predominant building material concrete it is necessary to identify less expensive substitute and
competitive to conventional concrete. In the recent years the cost of sand has become high
because of non-availability in the near by construction site and the government had restricted not
to remove the sand form seashore areas. Sawdust ash represents a major component of solid waste.
To deal with these problems, new material concrete was developed: Sawdust ash concrete. This
paper deals with the study of sawdust ash replacing sand at different proportions in concrete for 7,
14, 28 and 45 curing. The compressive strength of concrete are studied by replacing the sand with
0, 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50 percentages of sawdust ash with superplastizer. A
comparison is made with the test results of normal concrete. SEM (scanning electron microscopy)
together with EDS (energy dispersive spectroscopy) is a versatile tool which can use to image
samples. Scanning electron microscope imaging facilities identification of sand and sawdust ash
constituents with greater contrast, and greater spatial resolution than for optical methods and
provide ancillary capability for element analysis and imaging. Scanning electron microscopy
analysis of the sand and sawdust ash is compared.
Key Words: Sawdust ash, scanning electron microscopy, energy dispersive spectroscopy,
compressive strength.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
110
INTRODUCTION
During the last decades it has been recognized with growing sawdust ash waste are of large
volume and that this is increasing year by year in the household , mills and factory‘s. Now a days
even in rice mills they are using sawdust for burning due to shortage of rice husk. In Chidambaram
a huge quantity of sawdust ash waste is produced in the near by rice mills and households are
dumped. On the other hand, one bucket of sawdust cost Rs 6.00 and we get sawdust ash with no
cost. The need for housing are estimated more cost and some construction materials like natural
sand are becoming rare. This waste storage disposals are becoming a serious environmental
problem especially for Chidambaram place disposal sites are lacking. Hence there is a need for
recycling more and more waste materials.
The most widely used fine aggregate for the making of concrete is the natural sand mined
from the riverbeds. However, the availability of river sand for the preparation of concrete is
becoming scarce due to the excessive nonscientific methods of mining from the riverbeds,
lowering of water table, sinking of the bridge piers, etc. are becoming common treats. The present
scenario demands identification of substitute materials for the river sand for making concrete. The
choice of substitute materials for sand in concrete depends on several factors such as their
availability, physical properties, chemical ingredients etc. In this paper, an attempt is made on the
use of sawdust ash as a part replacement of sand for the production of concrete.
Material Used
Cement: Ordinary Porland cement of 53 grades having specific gravity of 3.10 was used.
Sand: The sand used for the study was locally available river sand conforming to grading
zone III of IS: 383-1970.
Gravel: The coarse aggregate was a normal weight aggregate with a maximum size of
20mm IS: 456-2000.
Sawdust ash: The SDA used for this study was collected from the rice mills points in
Chidambaram taluk at Cuddalore District.
Mix proportion: The control mix of the concrete was designed with a mix ratio of cement
/water /Sand /Coarse of 1:0.48:1.66:3.61 by weight. The slump has maintained 30-40mm.
EXPERIMENTAL INVESTIGATION
Specific gravity
The results specific gravity of sand and sawdust ash mixture is given in Table 1.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
111
Parameter
Sand
Coarse
SDA
(S+10
%SD
A)
(S+20
%SD
A)
(S+30%S
DA)
(S+40%S
DA)
(S+50%S
DA)
Specific
gravity 2.65 2.7 2.5 2.67 2.6 2.61 2.55 2.54
Table.1 Specific gravity of sand and sawdust mixture
Sieve analysis
The results Fineness Modulus of sand and sawdust ash mixture is given in Table 2.
Paramet
er
San
d
SD
A
(S+10%S
DA)
(S+20%S
DA)
(S+30%S
DA)
(S+40%S
DA)
(S+50%S
DA)
Fineness
Modulus
2.2
1
1.7
8
2.2 2.1 2.0 1.9 1.85
Table.2 Fineness modulus of sand and sawdust mixture
Scanning electron microscopy of fine aggregate (Sand)
Scanning electron microscopy has distinct advantages for characterization of concrete, cement
and aggregate microstructure and in the interpretation of causes for concrete deterioration.
SEM(scanning electron microscopy) together with EDS (energy dispersive spectroscopy) is a
versatile tool which can used to image samples easily up to 50x and 500 microns magnification
and analyse fine aggregate (sand) is shown in Fig.1, Fig.2 and Table.3 .
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
112
Fig.1 SEM
(scanning electron microscopy) Fig.2 EDS (energy dispersive spectroscopy)
of fine aggregate (sand) of fine aggregate
(sand)
Table 3 Elements of Fine aggregate (sand)
SEM and EDS of Sawdust ash (SDA)
SEM(scanning electron microscopy) together with EDS (energy dispersive spectroscopy) is a
versatile tool which can used to image samples easily up to 5000x and 5 micron magnification
and analyse Sawdust ash (SDA) is shown in Fig.3 ,Fig.4 and Table 4.
Element % Weight % Atomic
Al 3.83 4.15
Si 85.51 89.09
Ca 5.70 4.16
Fe 4.97 2.6
Total 100.00
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
113
Fig.3 SEM (scanning electron microscopy)
of Sawdust ash (SDA)
Fig.4 EDS (energy dispersive spectroscopy)
of Sawdust ash (SDA)
Table 4 Elements of sawdust ash
Element % Weight % Atomic
Mg 2.14 3.15
Al 2.08 2.76
Si 45.94 58.67
Cl 2.49 2.52
K 5.98 5.49
Ca 12.25 10.97
Fe 3.23 2.88
Cu 9.63 5.44
Zn 10.25 8.92
Total 100
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
114
Compressive strength
The compressive strength of the concrete with sawdust ash are measured using 150mm cubes
tested at 7, 14,28 and 45 days for mix 1:1.66:3.61 at water cement ratio of 0.48.These results are
shown in Fig.5, Fig.6, Fig.7 and Fig.8.
Fig.5 compressive strength of cubes in 7 days curing
Fig.6 compressive strength of cubes in 14 days curing
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
115
Fig.5 compressive strength of cubes in 28 days curing.
Fig.6 compressive strength of cubes in 45 days curing
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
116
DISCUSSION OF TEST RESULTS
Fineness modulus
With the addition of sawdust ash, the fineness modulus decreases as the ash increases. Hence, the
fine aggregate with addition with sawdust up to 15% its starts binding up together because of its
fineness and had pozzolanic effect.
Compressive strength
The compressive strength test results for the concretes containing sawdust ash fine
aggregates of cubes according to their age are very similar to each other upto 15%. Concretes
containing Sawdust ash as fine aggregates, with a mixing ratio 5%, 10%, 15% displayed an
increase in compressive strength than that of plain concrete but decreases as the % of sawdust
increases respectively.
CONCLUSION
Based on the present study the following conclusion can be drawn:
1. Sawdust ash to the extent of 15 percent replacement of sand decreases the fineness
modulus of fine aggregate making it pozzolanic.
2. The sem analysis shows the microstructure which fills up the concrete porosity.
3. The EDS show that it as high silica when helps the concrete to get solidified early.
4. There is an increase in compressive strength of concrete for the replacement by
sawdust ash upto 15%. For 15 percent replacement, the compressive strength is
maximum for all 4 curing .Beyond this, the compressive strength reduces gradually. A
50% replacement, the strength is less than normal but even that can be used in the case
where less strength is required.
REFERENCES
1. Kenai S, Benna Y, Menadi B, The effect of fines in crushed calcareous sand on
properties of mortar and concrete. In proceedings of international conference on
Infrastructure regeneration and rehabilitation a vision for next millennium, Sheffield;
pp.253-61. (1999)
2. Fitzgerald O.A, He built a home of Sawdust-Concrete, In: Reprinted by the permission
from popular mechanics, copyright. (1948)
3. Paki Turgut, Cement composites with limestone dust and different grades of wood
Sawdust In: Building and Environment. (2006)
4. BMP Association Ltd. Building out of Sawdust concrete. (2008)
5. Elinwa, A.U., and Mahmood, Y.A., ―Ash from timber waste as cement replacement
material,‖ Cement and concrete Composites, V.24, No.2, pp.219-222. (2002)
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
117
6. Udocyo FF, Dashibil PU. Sawdust ash as concrete material. ASCE, 14(2):173-6.
(2002)
7. Emmanuel A. Okunade., ―The Effect of Wood Ash and Sawdust Admixtures on the
Engineering Properties of a Burnt Laterite – Clay Bricks‖ Journal of Applied Sciences
8(6):1042-1048. (2008)
8. Abdullahi, M., Characteristics of Wood ash/OPC Concrete. Leonardo Elect. Practices
Technol. (LEJPT), 5(8): 9-16. (2006)
9. Amu, O.O., I.K.Adewumi, A.L.Ayodele, R.A.Mustapha and O.O.OLAAnalysis of
California bearing ratio values of lime and wood ash stabilized lateritic soil.J.Applied
Sci., 5(8): 1479-1483. (2005)
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
118
DUCTILE BEHAVIOR REINFORCED CONCRETE BEAM –
COLUMN JOINTS SUBJECTED TO CYCLIC LOADING
A.Murugesan1 and G.S.Thirugnanam
2
1 Research Scholar, Department of Civil Engineering, Sona College of technology, salem-636005,Tamil
Nadu, India.
2 Assistant Professor and Head, Department of Civil Engineering, Institute of Road And
Transport Technology, Erode-638316,Tamil Nadu, India..
Email:1 [email protected] &
ABSTRACT
After the Killari earthquake in Maharashtra and the more recent one in Gujarat ,structural
engineers have woke up, rather belatedly, to the start realities the wrought by the seismic forces of
the structures. With a view to keep abreast of the rapid developments and extensive researches that
has been carried out in the field of earthquake resistant design of reinforced concrete building
continuous refinement in the analysis and design of earthquake resistant structures is being made.
When a RC moment-resisting frame is subjected to seismic load, the possible
inelasticity is concentrated either in beams or in the beam-column joint regions. The failure of
reinforced concrete structures in recent earthquakes in several countries has caused concern about
the performance of beam – column joint. It is subjected to large forces during severe ground
shaking and its behavior has a significant influence on the response of the structure.
This paper presents a review of the behavior of joints. Understanding the joint behavior is
essential in exercising proper judgments in the design of joints. The paper discusses about the
seismic actions on exterior joints and highlights theoretical parameters that affect joint
performance with special reference to bond and shear transfer. The seismic performance of the
reinforced concrete exterior beam-column joints designed for seismic loads as per IS 1893-2002
and detailed with rectangular hoop confinement in column and joints region as per IS 13920-
1993..
KEY WORDS: Beam-column joints, steel fibers, reinforced concrete, cyclic loading.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Many reinforced concrete (RC) buildings or frames built
between 1950‘s and 1970‘s functioning today in many
parts of the world do not satisfy the current seismic
design requirements prescribed by IS 13920-1993.This
type of RC buildings were designed to withstand only
gravity loads. Ductility of the structural members is
lacking in these buildings because detailing of
reinforcement was not adopted .The reinforcement in
the beam do not have adequate anchorage in the joint to
develop their full tensile strength. These issues are very
crucial when the RC-beam-column joints are designed.
The failure of beam-column joint loads to the collapse the structure.
Fig 1-Damage in Beam – Column joint
The strengthening of joints is necessary due to (i) poor detailing of joint
reinforcement. (ii) deficient materials and inadequate anchorage length of reinforcement
(iii)Improper confinement of joint region (vi)changes in current design detailing and (v)
Variation of loads due to frequency of earthquakes and in different earthquake zones. The
nature of damage observed in RC structures due to earthquake forces is as shown in Fig.1
The shear failure of beam-column joints is the primary cause of collapse of many
structures due to seismic forces. The shear failure occurs due to
(i) Lack of confinement in the Beam column joint
(ii) Design of weak column
(iii) Design of strong beam
The beam-column joint leads to failure in RC frames .In order to avoid such
failure and improve the joint performance strength confinement are provided according to
IS 13920-1993.
Non-seismic reinforcement detailing of joint
The non-seismic reinforcement detail of interior joint is shown in Fig-2. The
longitudinal reinforcement in beam is continuous and in column the reinforcement is
lapped with short length just above the floor level. The transverse reinforcement is
proportioned to prevent the shear or lap failures in joints. The stirrups are open and hoop
with 90o bends. Transverse reinforcement is provided in joints.
Failures in RC buildings as shown in Fig-1, the beam column joints lead to total
collapse. In order to strengthen the weak elements the structure is prepared with steel
fiber reinforced concrete.
Recent studies expressed about RC framed buildings suffered significant
strength loss in the beam column joint region during earthquake. Inadequate structural
detailing and other deficiencies in the structures fail particularly exterior beam column
joints.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Present study
The research work on seismic performance of reinforced concrete structures have
considered the structures designed as per Indian Standards of practice (IS 456-2000 and
IS 13920-1993).
This have been considered for analysis, design and detailing of the beam column
joints of a most regular and conventional RC structure subjected to seismic loading. Both
codes have an extensive use in Europe and South – East Asia which are prominently
seismic prone zones.
Moreover, previous earthquakes have demonstrated that due to sudden
discontinuity of the geometry, interior beam column joint are most vulnerable to seismic
loading.. Hence in this study the interior beam column joint has been chosen to study its
performance under seismic loading.
Analysis of the selected RC building frame (shown in Fig-3) has been carried out
and the exterior joint has been designed and detailed based on seismic design as per the
codal provision and adopting special ductile detailing. The specimens are designed
according to the available guidelines and gravity load design concept to fully earthquake
resistant design. A detailed experimental study has been carried out according to the
design considerations.
Fig 2 Non-seismic detailing of interior joint
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Specimen description
Total of two specimens have been designed. Grades of concrete and steel for the
specimens have been taken as M30 and Fe 415 respectively. The specimen is converted
1/5th model from prototype. All assembles have general and cross-sectional dimensions
length of column is 600mm and length of beam is 380mm with cross sectional of
(300x450)mm and (250x300)mm respectively. The top and bottom length from joint face
was chosen to match the bending moment distribution at the joint for which it was
designed.
Test set up and loading
The test set up has been arranged on the test floor so that the beam column joint in
horizontal resting on the floor. Each specimen was tested under reverse cyclic loading.
The column of the test assembly was placed in a loading frame. The column was centered
accurately to avoid eccentricity, the axial load in column through a hydraulic jack resting
on test floor. The reinforcement detail of specimens given in Fig 4. The axial load was
applied on the column through the hydraulic jack positioned between the column and one
of the bulk heads. The axial load was kept during the test. The lateral load was applied at
the beam tip using actuator is displacement control.
Dial gauge is used to measure the downward and upward displacement in beam.
Strain gauges were used to measure the strain at joint region in concrete. At a distance of
350mm from the face of column, the load was applied at the beam through hand operated
screw jack. By changing the screw jack on either side of the beam end apply positive
(downward) and negative (upward) loads. The proving ring was placed between loading
Fig-3 Plan and section for prototype
building
JOINT
JOINT
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
point and screw jack and used measure the applied beam forces. Screw jacks were placed
on the top and bottom beams for the loading frame.
The exterior beam column joint specimen was subjected to quasi-static cyclic
loading simulating earthquake loads. The history of load sequence followed for the test
was presented in Fig-5. The load was applied by using screw jack totally 15 cycles were
imposed. The cyclic load versus deflection diagram was calculated. This was presented in
Fig-6.a
The beam column was gradually loaded by increasing the load level during each
cycle. The observed deflection was greater than it was in earlier cycle. As the load level
was increased further cracks were developed in other portions.
Ductility of a structure is its ability to undergo deformation beyond the initial
yield deformation, while still sustaining load. This is illustrated in the load versus
deflection diagram (Fig-6.b). The first yield deflection is assumed as bilinear behavior of
the beam which is obtained both forward and backward cycles (Fig-7 & Fig-8). When a
structure is subjected to reverse cyclic loading cumulative ductility up to any load point is
defined as the sum of the ductility at maximum load level attained in each cycles up to
the cycle considered (Fig.9& 10)
The reinforced details of the specimens are also presented in table 1.
TABLE 1
CODE PROTOTYPE 1/5
TH
MODEL
IS
13920-
1993
For Beam:
Size : 250x300
mm
Main
reinforcement:
4 nos.12mm
(Ast -452mm2)
Top
For Beam:
Size : 120 x
125 mm
Main
reinforcement:
2 nos.8mm
(Ast -
101mm2)
Top
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
reinforcement:
4 nos.12mm
(Ast -452mm2)
Shear
reinforcement:
8mm at 100mm
c/c
For Column:
Size : 300 x 450
mm
Longitudinal
reinforcement:
6 nos.20mm
(Ast-1885mm2)
Lateral ties:
8mm at 100mm
c/c
reinforcement:
2 nos.8mm
(Ast -
101mm2)
Shear
reinforcement:
8mm at 25
mm c/c
For Column:
Size : 120 x
225 mm
Longitudinal
reinforcement:
4 nos.12mm
(Ast-452mm2)
Lateral ties:
8mm at 25
mm c/c
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
During heavy wind or earthquake some energy is absorbed in each load cycle, the
relative energy absorption capacities during various load cycles were calculated. The
relative energy absorption capacity and cumulative energy absorption capacity of the
beam was obtained by adding the energy absorption capacity.
Then Stiffness for both forward and backward cycles is calculated (Fig.11 to 24).
Fig 5 - Loading Sequence Diagram
Fig.4- Reinforcement details of specimen
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Fig. 6.b- Load-Deflection Diagram-Right side
Fig 6. a -Load- Deflection Diagram-Left side
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Fig 7 Variation of Ductility Factor with Forward Load Cycles-Left Side
Fig 8 Variation of Ductility Factor with Backward Load Cycles-Left Side
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Fig 9 Variation of Cumulative Ductility Factor with Forward Load Cycles-Left side
Fig 10 Variation of Cumulative Ductility Factor with Backward Load Cycles-Left Side
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Fig 11 Variation of Cumulative Ductility Factor with Forward Load Cycles-Right Side
Fig 12 Variation of Cumulative Ductility Factor with Backward Load Cycles-
Right Side
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Fig 13 Variation of Relative Energy Absorption Capacity with Forward Load
Cycles-Left Side
Fig 14 Variation of Relative Energy Absorption Capacity with Backward Load
Cycles-Left Side
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Fig 15 Variation of Relative Energy Absorption Capacity with Forward Load
Cycles-Right Side
Fig 16 Variation of Relative Energy Absorption Capacity with Backward Load
Cycles-Right Side
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Fig 17 Variation of Cumulative Energy Absorption Capacity With Forward Load
Cycles-Left side
Fig 18 Variation of Cumulative Energy Absorption Capacity With Forward Load
Cycles-Left side
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Fig 19 Variation of Cumulative Energy Absorption Capacity with Forward Load
Cycles-Right side
Fig 20 Variation of Cumulative Energy Absorption Capacity With Backward
Load Cycles-Right side
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Fig 21 Variation of Stiffness with Load Cycles – Forward Cycles-Left side
Fig 22 Variation of Stiffness with Load Cycles –Backward Cycles-Left side
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Fig 23 Variation of Stiffness with Load Cycles –Forward Cycles-Right side
Fig 24 Variation of Stiffness with Load Cycles –Backward Cycles-Right side
CONCLUSION
An experimental study was carried out on Beam-Column Joints which are tested
under reverse cyclic loading. Based on the investigation reported, the following
conclusions are drawn. They are summarized below.
The crack was appeared on the beam with a load of 8.2 KN during First cycle.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
The crack was appeared at beam column joint with a load of 11.2 KN during
Second cycle.
The ultimate load carrying capacity was reached at 15 KN during Second cycle.
REFERENCES
1. Andre Filiatrault, Sylvain Pineau, and jules Houde ―Seismic Behavior of steel-
fibre Reinforced Concrete Interior Beam-Column Joints‖, ACI Structural Journal,
V.92, No.5, Sep-Oct 1995, pp 543-552.
2. Bing Li, Yiming Wu and Tso – Chien ―Seismic Behaviour of Nonsensically
detailed Interior beam – wide column joints – part II; theoretical comparisons and
analytical studies‖ The ACI structural journal, Jan-Feb 2003, pp 56-65.
3. Kitayama.K, Otani.S and Aoyama.H, ―Design of Beam – Column joints for
Seismic resistance ‖ ACI SP -123, American Concrete Institute, Michigan,
1991,pp 97-123.
4. Leon R.T ―Shear strength and Hysteric Behaviour of Interior Beam – column
joints‖ The ACI structural journal, V.87, 1990,pp 3-11.
5. Lee.D, Wight.J.K, and Hanson, R.D. ―Original and Repaired Beam – Column
Sub Assemblages Subjected to Earthquake type Loading‖ Report No. UMEE –
7654, Department of Civil Engineering, University of Michigan, April 1976.
6. Murthy C.V.R, Durgesh C.Rai, K.K.Bajpai and Sudhir.K.jain, ―Anchorage
Details and Joint Design in Seismic RC Frames‖, the Indian Concrete Journal,
April 2001, pp 274 – 280.
7. Paul S.Baglin and Richard H.Scott ―Finite Element modeling of Reinforced
Concrete Beam – column connections‖, ACI Structural Journal, V.97, No.6, Nov-
Dec 2000.
8. Park, R., Paulay, T. ―Reinforced Concrete Structures, New York, John Wiley &
Sons, 1975.
9. Pantazopoulou.s and Bonacci.J, ―Considerations of questions about Beam-column
joints‖ The ACI journal, V.89, 1992, pp 27-36.
10. Prota.A, A.Nanni, G.Manfredi, E.Cosenza ―Seismic Upgrade of Beam-column
Joints with FRP Reinforcement‖, Industria Italiana del Cemento, Nov 2000.
11. Subramanian.N & D.S.Prakash Rao ―sesmic design of joints in RC structures – A
review‖, ICJFeb-2003, pp 883-892.
12. Sathiskumar.S.R, B.Vijya Raju and G.S.B.V.S.Rajaram ―Hysteretic behaviour of
lightly Rainforced Concrete exterior Beam-column joint sub-assambalages‖,
Journal of Structural Engineering, Vol.29, No.1, Apr-Jun 2002, pp31-36.
13. Shingeru Hakuto, Robert Park and Hitoshi Tanaka ―Seismic Load Tests on
Interior and External Beam-column joint with substandard Reinforcing Details‖
The ACI structural Journal, V.97, No.1, Jan-Feb 2000.
14. Safaa Zaid, Hitoshi Shiohara and Shunsuke Otani ―Test of a Joint Reinforcing
Detail Improving Joint capacity of R/C Interior and Exterior Beam-column Joint‖
The 1st Japan-Korea joint seminor on Earthquake Engineering for Builing
structures, Oct.30-31, 1999, Faculty Club House, Seoul National University,
Seoul, Korea.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
CORROSION MONITORING OF ELECTRIC TRANSMISSION
LINE TOWER FOUNDATIONS AND EVALUATION METHODS
- A CASE STUDY
S.Christian Johnson* Dr.G.S.Thirugnanam**
ABSTRACT
At present in India 2, 65,000 circuit kilometers of Transmission line are forming
the transmission and distribution network. Mostly these lines are running through open
lands or dense forests with extreme climatic conditions. Further many transmission lines
pass through the coastal lines and this has a very adverse effect on the life of the
transmission lines.(India‘s coastal length is about 7527 Km).
Transmission line tower is considered to be the most stable and versatile semi-
permanent structure which once erected in the open space, serves the power system for
years together most faithfully, facing the vagaries of nature. However, sometimes like
other components of the power system, the transmission line towers also fails, resulting
into disruption to the transfer of large blocks of point of view. Many of these failures are
corrosion related due to the exposure of the system materials to aggressive atmospheric
and/or soil environments. One of such failures is the corrosion of transmission line tower
legs below ground level.
In this paper corrosion monitoring and evaluation methods applicable to
transmission line towers are discussed.
Few case studies have been described dealing with visual assessment of stub
corrosion in transmission line tower foundations.
Factors like improper selection of tower and tower foundation, poor grade of
concrete, inferior quality of concrete, insufficient curing of coping/muffing concrete,
wrong shape of coping, corrosive environments, stray current mechanism etc.,. which are
noticed in visual study are discussed.
Corrosion monitoring undertaken in certain locations in the state of Tamil nadu
using half cell potentiometer test is also presented.the corrosion levels using half cell
potentiometer.
* - Research Scholar
** - Assistant Professor and HOD, Dept. of civil Engineering, IRTT, Erode.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
INTRODUCTION
The reliability of the electric power system is essential in the modern
world. Failures in their transmission line components amounts to thousands of dollars
only in maintenance costs apart from other related expenditures. Many of these failures
are corrosion related due to the exposure of the system materials to aggressive
atmospheric and/or soil environments .One of such failures is the corrosion of
transmission line tower legs at and below the ground level. The condition of these
components is essential, since the disintegration will provoke the collapse of the tower or
other towers in the vicinity, with the consequences associated, i.e. suspension of the
electrical supply.
As a part of a research work on ― Durability of tower foundations‖ half
cell potentiometer readings were taken in the transmission towers in certain c\selected
locations in Tamil Nadu. Before measurements, visual inspection above ground level
were made in tower legs.
VISUAL INSPECTION
The most common method of power line inspection is visual assessment,
performed from the ground by foot- patrol or from the air during routine helicopter
surveillance. This is the most rigorous method since it allows determination of the extent
and type of corrosion attack, including possible involvement of microbial induced
corrosion.
The techniques and methods used to gauge the corrosion attack are
standard and excellent instruments for field and /or laboratory use are readily available.
Breakdown of the protective coating coating occurs usually by a combination erosion and
physical damage. The extent (loss of thickness)of an intact coating can be measured by
variety of methods.These include destructive (scribing ,)magnetic pull –off ,magnetic
flux, eddy current ultrasonic techniques ,etc.,,
Case study on visual assessment of Corrosion in transmission line tower
legs/foundations:
An elaborate discussion with the official of TNEB and reconnaissance survey in
certain transmission tower locations in the state of Tamilnadu had been conducted and
some the causes for the durability related distresses in stub/coping concrete of
transmission line towers had been identifie
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
1) Improper formation of chimney:
The concrete above the ground level ( Chimney concrete should have a
muffing portion which is slantingly formed. This causes stagnation of water on
the chimney leading to pitting corrosion.
Fig.2 Improper formation of chimney Fig.3.Formation of pitting corrosion
2)In sufficient curing of coping concrete and poor quality of material and
construction ( Fig.4.& 5)`
3)Ingress of water /pollutants through the concrete and stub angle interface:
Due to ingress of saline water or other pollutants etc., the stub top part of
the chimney gets corroded. This leads to the formation of local cracks and chip
off, which allows salt to penetrate further into the affected stub where the process
of corrosion will be more and more accelerated as in the figures ( 6& 7) below.
Fig.6 Saline water resulted in bulging of steel Fig.7.Severe pitting corrosion
ERECTED DURING 2008 (STUB STARTS
CORRODED) 110KV ARS – PLDM #
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
4)Corrosive Environments:
The location where subsoil water salinity is very severe, there are
chances of rusting of tower stub encased in the concrete as well as above the
ground level. Corrosion of stub angle just above the muffing or within the
muffing is very common in saline areas or water stagnated areas.This is very
much prevalent in Tamilnadu state wherever corrosive environment is
confronted as in the following figures ( 8&9)
Fig. 8 & 9.Towers standing on corrosive environments
5) Bush /fern growth in and around tower muffing area: ( Fig. 10&11)
Fig. 10 &11 Intensive growth of fern and grass in and around the tower foundation
6) Stray current mechanism:
Leakage currents from power conductors through insulator strings to tower
invariably exist in variable magnitude depending on voltage intensity, insulator
surface contamination and atmospheric moisture. In addition, due to induction in
ground wires from the tree phases, resultant induced current flows through the loop
formed by ground wire, the two towers at each end of the span and the ground
underneath the span.( Fig 12 &13)
Fig.12 &13). Invisible stray currents leads to corrosion
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Structure and enters the ground through the water electrolyte. This results in more
or less uniform attack on tower metal where discrete anodic and cathodic sites or areas do
not exist. Both anodic and cathodic polarization process equally control the corrosion
rate.
A mechanism of pitting or crevice corrosion will initially occur in the
presence of aggressive ions such as chlorides. These ions are responsible in the formation
pits on the surface, which accelerates corrosion attack. An important consequence of
pitting is that the localized attack may be very severe; this may lead to structural
catastrophe.
7)Location of tower:
The location of tower in the bank of river and agricultural field, etc.,
(Fig.14&15) plays a major role in durability based distresses in tower foundations.
Fig14.. Tower spot on the bank of river Fig.15 Tower in the marshy land
8) Under sizing of foundation due to wrong classification of soil.
For example, the soil may be dry black cotton but the foundation cast
may be that for normal dry soil, if the corrective measures are not
taken, the foundation can fail.
Half-cell Potential potentiometer test:
Basic Concept: This method is sometimes called the corrosion potential or rest
potential method. The objective of this method is to measure the voltages that are present
over rebar in concrete. The half-cell is a hollow tube containing a copper electrode and
immersed in copper sulfate solution. The bottom of the tube is porous and is covered in a
sponge material. The copper sulfate permeates this sponge that can then be placed on a
concrete surface allowing an electrical potential (voltage) to be measured. The objective
of the method is to measure the voltage difference between the rebar and the concrete
over the rebar. Large negative voltages (-350mV) indicate that corrosion may be taking
place. Voltages smaller than about -200 mV generally mean corrosion is not taking
place.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Figure 16. Half-cell measuring circuit for detecting rebar corrosion.
Data Acquisition: Half-cell surveys simply require making an electrical connection to the
rebar and then taking readings over the area of interest by pressing the sponge of the
reference electrode against the concrete and observing the voltmeter reading. The
readings are usually taken on some type of predetermined grid system. A device called a
potential wheel is sometimes used. This provides a wheel for the tip of the half-cell and
allows continuous readout of corrosion potentials, making the method quite rapid. To
ensure that sufficient electrolyte is present at the surface, it is usual for all of the reading
locations to be pre-wet using a fine spray of weak detergent mixture. A half-cell
instrument is shown in figure 16.
Data Processing: Since the survey directly measures the quantity of interest (namely
voltage), no data processing is required. The data may be plotted on a map and contoured
for ease of interpretation and for presentation purposes.
Data Interpretation: Experience has shown that for potentials whose magnitude is greater
than -350 mV, there is a 90% probability that corrosion is active. If the magnitude of the
potential is less than -200 mV, then there is a 90% probability that corrosion is not
active.
Figure 17. Example Half-cell Potential results. (Hammand Concrete Testing)
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Limitations: Several factors must be kept in mind when conducting and interpreting half-
cell measurements. It is important to consider the oxygen and chloride concentration and
the resistivity of the concrete, all of which can influence the readings. Adding to these
complications are the advances in concrete and repair technologies, such as dense
material overlays, concrete sealers, corrosion inhibitors, chemical admixtures, and
cathodic protection systems. It is important to understand and consider these
complicating factors during a half-cell survey and to supplement the results with other
nondestructive surveys. With most of the current equipment, an electrical connection has
to be made with the rebar. However, some recent developments involve the
measurement of potential gradients using two reference electrodes, eliminating the need
to make direct electrical contact with the rebar.
Case study on health monitoring of transmission line towers in Tamilnadu:
As on 31St March 2008, the state of Tamilnadu has an EHV network as
follows. 230 kV- 6856 ckm, 110 kV – 12765 ckm, 66 kV – 1196 ckm,Totaling 20817
ckm. Supported by around 60000 transmission line towers. . These towers are of a variety
of designs and were constructed to different specifications. The oldest structure still in
service is more than 75 years old. Some of the transmission line towers have been in
service for more than 40 to 50 years old and are experiencing deterioration on various
accounts. Many transmission lines pass through the coastal lines and this has a very
advesre effect on the life of the transmission lines. Indias coastal length is about 7527 Km
and Tamil nadu‘s is 1076 Km.
Fig.18: Half cell potentiometer test in actual field
Half cell potentiometer test is carried on actual field tower foundation in its
coping portion. During measurement, the coping concrete surface must be wetted by
water, so as it facilitates uniform flow of current between anode and cathode terminals of
half-cell potentiometer instrument.
Measurements on transmission line tower legs of coastal and inland areas in
Tamil nadu had been taken. The results had been compared with laboratory tests are
presented and can be related to different corrosion conditions:
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
For the coastal study, following lines have been taken.
1. ETPS- Manali – (110 kV line ), 1971
2. ETPS- Manali - (230 kV line)
3. NCTPS- Thandiyarpet ( 230 kV Line )
4. Thiruthoraipoondi- Vaimedu ( 66 kV Line ), 1979`
5. Thiruturaipoondi – Vaimedu ( 110 kV Line ), 2004
For inland study following lines have been taken.
1. Mettur- Gobi (110 kV line)
2. MTPS- Mettur Auto SS (230 kV) Line
From the above mentioned lines potential values are obtained and are tabulated
below.
Table - Half cell potentiometer Readings.
TOWER
Leg
-1
Leg-
2
Leg-
3
Leg-
4 Remarks
Coastal area:
Ennore–
Manali 110
kV Line
-
633 -620 - 677 -645
Indication of more than
90% corrosion
-do- (230 kV
line)
-
610 -612 -608 -627 -do-
NCTPS-
Thandiyar
pet 230 kV
Line(36)
-
220 -245 -234 -218
Since this is newly
erected one , less
corrosion
-do- (35) -
458 -463 -456 -467
Though new, its
location and the
quality of concrete is
the cause
Thiruthoraip
oondi-
Vaimedu 66
-
More tthan 90 %
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
kV line ( 9) 543 -453 -457 -650 corrosion
-do- (7) -
527 -530 -470 -403 -do-
-do- 110
kV Line (7)
-
235 -232 -253 -279
Less than 50 %
corrosion.
Inland area:
Mettur- Gobi
110 kV (58)
-
275 -287 -259 -268
Less tha n 50 %
corrosion
MTPS-
Mettur Auto
SS (230 kV)
Line
-
225 -209 -202 -213 -No corrosion-
WEIGHT LOSS PERCENTAGE METHOD:
W1-W2
% of wt. loss = --------- X 100
W1
Where, W 1 = Initial weight of angle specimen
W 2 = Final weight of angle specimen
While determining weight loss, the angle specimen surface should be thoroughly
cleaned using cleaning solution or by using emery sheet and hence the accuracy in weight
should be attained.
LINEAR POLARIZATION RESISTANCE :(LPR)
Basic Concept:
Linear Polarization Resistance (LPR) provides a relationship between the voltage
(potential) and current density of a material. The polarization resistance of a material is
defined as the slope of the potential-
potential. There are a number of ways to carry
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
out the LPR measurement. Perhaps the simplest is to use two nominally identical
electrodes. A small potential difference (e.g., 20 mV) is applied to these electrodes, and
the resulting current is measured. This current is proportional to the inverse of the
polarization resistance and, hence, is directly proportional to the corrosion rate.
Limitations:
For the steel in a concrete system, it is imperative that sufficient time is allowed
for a current value to stabilize at a certain potential (or vice versa). For example, in the
potentiostatic LPR technique, it will typically take several minutes for the current to
reach a stable level after the polarizing voltage is applied. Shorter polarization could lead
to significant measurement errors.
Figure 19. Example Tafel graph.
GALVANOSTATIC PULSE TECHNIQUE:
Basic Concept:
In this technique, an anodic current pulse is imposed onto the rebar for a short
period of time, using a counter electrode positioned on the surface of the concrete. The
resultant rebar potential change (E) is recorded by means of a reference electrode, also
located on the concrete surface. Typical current pulse duration (t) and amplitude have
been reported at 3s and 0.1 mA respectively.
Data Acquisition and Interpretation:
The slope of the potential-vs-time curve (E/t) measured during the current pulse
can be used to provide information on the rebar corrosion state. Passive rebar reportedly
has a relatively high slope, whereas rebar undergoing localized corrosion has a very small
slope. In the latter case, the rebar potential only shifts by a few millivolts under the
applied current pulse. It is also possible to use the potential data to obtain a measure of
the concrete resistivity (for a given depth of cover). The technique is reportedly very
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
rapid and may facilitate more unambiguous information on the rebar corrosion state than
is possible by simple potential mapping. Figure 20 shows the GalvaPulse© instrument
which is manufactured by Germann Instruments.
Figure 20. GalvaPulse© instrument. (Germann Instruments)
ELECTROCHEMICAL NOISE METHOD:
Basic Concept:
Unlike other electrochemical techniques, noise measurements do not rely on any
"artificial" signal imposed on the rebar probe elements. Rather, natural fluctuations in the
corrosion potential and current are measured to acterize the severity and type of corrosive
attack. For these measurements, three nominally identical rebar probe elements can be
conveniently embedded in the concrete.
Data Acquisition:
There may be some reluctance to using electrochemical noise for rebar corrosion
measurements in the field due to a perceived "over sensitivity" of the equipment and fears
of external signal interference. Although such concerns may be justified in certain cases,
and this technology is relatively new to the rebar field, it has recently been used
successfully in rebar corrosion measurements in the Vancouver harbor and in clarifier
tanks of the paper and pulp industry in British Columbia. In these applications, the rebar
noise probes were embedded in large (up to 4 meters long) concrete prisms. These
prisms were partially submerged and exposed to seawater and to the effluent solution in
the clarifiers.
Electrochemical noise data showed increased corrosion activity associated with
the tidal cycle in the Vancouver harbor. In this case, the highest corrosion activity on the
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
probe element, located in cracked concrete, occurred as the tide level approached that of
the crack. Under these conditions, seawater is available to penetrate the concrete as
corrosive electrolyte, together with a high degree of aeration, a combination expected to
stimulate electrochemical corrosion processes. Noise data from electrodes placed in
cracked and uncracked concrete and exposed to pulp and paper effluent confirmed that,
as expected, the presence of cracks facilitated more rapid diffusion of corrosive species to
the rebar surface and led to higher electrochemical corrosion activity. To date, no
significant interference or other problems have been encountered in the noise
measurements of these two field exposure programs.
Data Processing and Interpretation:
Apart from the interpretation of the "raw" noise data, it has become customary to
conduct further statistical data processing, spectral analysis, and chaos theory analysis.
Such data treatment serves to reduce the volume of data and to assist in distinguishing
different forms of corrosion from one another.
Advantages:
A distinct advantage of the electrochemical noise techniques is that the initiation
and propagation of corrosion pits can be clearly identified. Distinct pit initiation
transients, comprised of a sharp signal increase with passive film breakdown and a more
gradual recovery of the signal to baseline levels as the passive film repairs itself, were
observed for a carbon steel rebar probe exposed to chloride containing concrete pour
solution. These distinct signatures of the initiation of corrosion pits were evident long
before the attack was observable by visual means, indicating the "early warning"
capabilities of this technology.
ACOUSTIC EMISSION METHOD:
Basic Concept:
Acoustic emissions (AE) monitoring of concrete has been used to detect rebar
corrosion and has been shown to detect film cracking, gas evolution, and microcracking.
Although attenuation of the AE signal in concrete has been a concern in the past,
placement of the AE transducers on the reinforcing steel and using the steel as a sound
propagation medium should allow the onset of steel corrosion to be detected. It is also
possible to use the AE method to calculate the location where the steel corrosion is
occurring. This appears to be a promising technique that can be used as a bridge
inspection method to quantify the condition of steel-reinforced concrete where corrosion
is occurring.The AE method measures the high-frequency acoustic energy that is emitted
by an object that is under stress. Slow crack growth in ductile materials produces few
events, whereas rapid crack growth in brittle materials produces a significant number of
high amplitude events. Corrosion product buildup and subsequent microcracking of the
concrete represents the latter phenomenon.
Data Acquisition and Processing:
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
A typical AE monitoring system uses piezoelectric sensors acoustically coupled
to the test object with a suitable acoustic coupling medium, (grease or adhesive). The
output of the sensors is amplified and filtered by pre-amplifiers and then fed to the
monitor via shielded coaxial cables. The monitor further filters and amplifies the AE
signals, processes the data, and displays the results. Both results and raw data are
typically recorded for archival purposes or for post-test analysis, for instance, to
determine location of the AE signal.
CONCLUSIONS:
By visual observation carried out in this work, possible causes for
formation of corrosion in tower legs/foundations have been identified.
A kind of Pitting/crevice corrosion noticed in the stub angle /coping
interface is much alarming and so identification of suitable refurbishment
methodology is the need of the hour.
An effective approach to design the concrete and stub angle with suitable
admixture and coatings have to be studied.
Effectiveness of umbrella formation in the coping concrete using steel or
fibre wrapping have to be explored.
Proper method of formation of coping and its curing have to be
emphasized.
Half cell potentiometer readings taken in tower legs are in line with the
corrosion assessment made by visual inspection.
The authorities in power department can use the half cell potentiometer
test to diagnose the intensity stub angle corrosion in the foundation for
implement maintenance works.
Applicability of other corrosion monitoring and evaluation methods
mentioned in this paper can also be verified in the field but beyond the
scope of this work
REFERENCES:
1.) David Huughes ,‖Monitoring steel tower foundation corrosion utility uses
polarization resistance,condition assessment technique‖Aug 1,1996 12:00pm
2) Dhir.RK, M.R.Jones and M.J MCCarthy ‗Chloride-induced reinforcement
corrosion‘, Magazine of Concrete research, 46, No.169, Dec 269-277, March 1994.
3) Gracia.E et.al ―Corrosion monitoring of electrical transmission line tower legs by
Electrochemical Methods‖.email:[email protected]
4) Health monitoring of transmission line tower foundations. BE Project of T.Mythili
from Institute of Road and Transport Technology. Erode-16.
5) K.Sargunan, Study on failure of transmission line tower foundation and remedial
measures, M.E.Project, July 2009, IRTT, Erode.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
PROPERTIES OF BRICKS WITH PARTIAL REPLACEMENT OF
BRICK EARTH BY STEEL SLAG
P.S.Kothai
Senior Lecturer, Kongu Engineering College,Perundurai,Erode
Dr.R.Malathy
Principal, Excel Engineering College, Komarapalayam
ABSTRACT
Bricks are like an artificial stone obtained by moulding clay in rectangular blocks of
uniform size ( 19cm x 9cm x 9cm )and then by drying and burning these bricks. Brick earth is
an important constituent in brick manufacturing. Increased utilization of natural soil for the
manufacturing of bricks results in the depletion of natural resources. Hence there is a need for
conserving resources and environment and for proper utilization of energy. There has been an
emphasis on the use of wastes and industrial by products in all areas including construction
industry. Steel slag, a waste material from steel manufacturing industries may be used as a
partial substitute material for brick earth in brick manufacturing without any deleterious effect.
The study on physical and mechanical properties of steel slag bricks with partial replacement
of brick earth by steel slag shows that the steel slag can be effectively used in brick
manufacturing.
INTRODUCTION
Brick earth is an important constituent in brick. All along in India, we have been using
natural soil in brick manufacturing. The infrastructure development such as power projects and
industrial developments have started now. Availability of natural soil is getting depleted and
also it becoming costly. There is need for conserving resources and environment and for
proper utilization of energy. Hence, there has to be an emphasis on the use of wastes and by-
products in all areas including construction industry. Here in this research work an attempt is
made to utilize steel slag, a waste material from steel manufacturing industry in bricks as a
partial replacement material for soil.
LITERATURE REVIEW
(1)A comprehensive study of the potential health risks associated with the
environmental applications ( eg. fill, road base , landscaping ) of iron and steel making
slag was performed using characterization data for 73 samples of slag collected from
blast furnaces, basic oxygen furnaces and electric arc furnaces. Characterization data
were compared to regulatory health based ―screening‖ bench marks to determine
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
constituents of interest. Antimony, Beryllium, Cadmium, Trivalent & hexavalent
chromium, Manganese, Thallium and Vanadium were measured above screening levels
and were assessed in an application –specific exposure assessment using standard U.S.
Environmental Protection Agency risk assessment methods. A stochastic analysis was
conducted to evaluate the variability and uncertainty in the inhalation exposure and risk
estimates, and the oral bio accessibility of certain metals in the slag was quantified. The
risk assessment found no significant hazards to human health as a result of the
environmental applications of steel-industry slag.
(2)Environmental scientists and toxicologists completed an industry-wide
"Human Health and Ecological Risk Assessment (HERA)". Based on worst case
exposure assumptions the HERA demonstrated that iron and steel slag poses no
meaningful threat to human health or the environment when used in a variety of
residential, agricultural, industrial and construction applications. Consequently, the
metals in the slag matrix are not readily available for uptake by humans, other animals or
plants, do not bio-accumulate in the food web and are not expected to bioconcentrate in
plant tissue. Slag has been safely and successfully used as a construction aggregate in
many applications such as asphaltic concrete, Portland cement concrete, roadway
embankment and shoulders and on unpaved roads, parking lots, walkways, and
driveways. Non-construction related applications include the Portland cement production,
agricultural applications such as soil remineralization, pH supplement liming agent, for
treating acidic run-off from abandoned mines and for remediation of industrial waste
water run-off.
(3) Steelmaking slag -- specifically slag generated from EAFs. BOFs, and BFs
during the iron/steel making process -- has many important and environmentally safe
uses. In many applications, due to its unique physical structure, slag outperforms the
natural aggregate for which it is used as a replacement. Hence, not only does slag offer a
superior material for many construction, industrial, agricultural, and residential
applications, but the use of slag promotes the conservation of natural resources. As a
result, the market for slag has remained strong and, as further applications are promoted,
is expected to grow. The existence of this market and the broad variety of potential uses
offered by steelmaking slag demonstrate that it is clearly a safe, useful and valuable
product and not a "solid waste."
MATERIAL DESCRIPTION
Brick:
The term brick refers to small units of building material, often made from fired clay
and secured with mortar, a bonding agent comprising of cement, sand, and water. Long a
popular material, brick retains heat, with-stands corrosion, and resists fire. Because each unit is
small usually four inches wide and twice as long, brick is an ideal material for structures in
confined spaces, as well as for curved designs. Brick making improvements have continued
into the twentieth century. Improvements include rendering brick shape absolutely uniform,
lessening weight, and speeding up the firing process. For example, modern bricks are seldom
solid. Some are pressed into shape, which leaves a frog, or depression, on their top surface.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Others are extruded with holes that will later expedite the firing process by exposing a larger
amount of surface area to heat. Both techniques lessen weight without reducing strength.
Raw Materials:
Natural clay minerals, including kaolin and shale, make up the main body of
brick. Small amounts of manganese, barium, and other additives are blended with the
clay to produce different shades, and barium carbonate is used to improve brick's
chemical resistance to the elements. Many other additives have been used in brick,
including by products from papermaking, ammonium compounds, wetting agents,
flocculants (which cause particles to form loose clusters) and deflocculates (which
disperse such clusters). Some clays require the addition of sand or grog (pre-ground, pre-
fired material such as scrap brick).A wide variety of coating materials and methods are
used to produce brick of a certain colour or surface texture. To create a typical coating,
sand (the main component) is mechanically mixed with some type of colorant.
Sometimes a flux or frit (a glass containing colorants) is added to produce surface
textures. The flux lowers the melting temperature of the sand so it can bond to the brick
surface. Other materials including graded fired and unfired brick, nepheline syenite, and
graded aggregate can be used as well.
Steel slag:
Steel slag, a by-product of steel making, is produced during the separation of the
molten steel from impurities in steel-making furnaces. The slag occurs as a molten liquid melt
and is a complex solution of silicates and oxides that solidifies upon cooling. Virtually all steel
is now made in integrated steel plants using a version of the basic oxygen process or in
specialty steel plants (mini-mills) using an electric arc furnace process. The open hearth
furnace process is no longer used.In the basic oxygen process, hot liquid blast furnace metal,
scrap, and fluxes, which consist of lime (CaO) and dolomitic lime (CaO.MgO or ―dolime‖),
are charged to a converter (furnace). A lance is lowered into the converter and high-pressure
oxygen is injected. The oxygen combines with and removes the impurities in the charge. These
impurities consist of carbon as gaseous carbon monoxide, and silicon, manganese, phosphorus
and some iron as liquid oxides, which combine with lime and dolime to form the steel slag. At
the end of the refining operation, the liquid steel is tapped (poured) into a ladle while the steel
slag is retained in the vessel and subsequently tapped into a separate slag pot.
There are many grades of steel that can be produced, and the properties of the steel slag
can change significantly with each grade. Grades of steel can be classified as high, medium,
and low, depending on the carbon content of the steel. High-grade steels have high carbon
content. To reduce the amount of carbon in the steel, greater oxygen levels are required in the
steel-making process. This also requires the addition of increased levels of lime and dolime
(flux) for the removal of impurities from the steel and increased slag formation.There are
several different types of steel slag produced during the steel-making process. These different
types are referred to as furnace or tap slag, raker slag, synthetic or ladle slags, and pit or
cleanout slag.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
The steel slag produced during the primary stage of steel production is referred to as
furnace slag or tap slag. This is the major source of steel slag aggregate. After being tapped
from the furnace, the molten steel is transferred in a ladle for further refining to remove
additional impurities still contained within the steel. This operation is called ladle refining
because it is completed within the transfer ladle. During ladle refining, additional steel slags
are generated by again adding fluxes to the ladle to melt. These slags are combined with any
carryover of furnace slag and assist in absorbing deoxidation products (inclusions), heat
insulation, and protection of ladle refractories. The steel slags produced at this stage of steel
making are generally referred to as raker and ladle s Pit slag and clean out slag are other types
of slag commonly found in steel-making operations. They usually consist of the steel slag that
falls on the floor of the plant at various stages of operation, or slag that is removed from the
ladle after tapping. Because the ladle refining stage usually involves comparatively high
flux additions, the properties of these synthetic slags are quite different from those of the
furnace slag and are generally unsuitable for processing as steel slag aggregates. These
different slags must be segregated from furnace slag to avoid contamination of the slag
aggregate produced. In addition to slag recovery, the liquid furnace slag and ladle slags are
generally processed to recover the ferrous metals. This metals recovery operation (using
magnetic separator on conveyor and/or crane electromagnet) is important to the steelmaker as
the metals can then be reused within the steel plant as blast furnace feed material for the
production of iron. lags.
Properties of Steel slag:
Steel slag aggregates are highly angular in shape and have rough surface texture.
They have high bulk specific gravity and moderate water absorption (less than 3 percent).
Table -1 list some typical physical properties of steel slag.
Physical composition:
Property Value
Specific Gravity >3.2 - 3.6
Unit Weight, kg/m3 (lb/ft
3)
1600 - 1920
(100 - 120)
Absorption up to 3%
Table 1-Typical physical properties of steel slag
Chemical composition:
Constituent Composition (%)
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
CaO 40 - 52
SiO2 10 - 19
FeO 10 - 40
(70 - 80% FeO, 20 - 30% Fe2O3)
MnO 5 - 8
MgO 5 - 10
Al2O3 1 - 3
P2O5 0.5 - 1
S < 0.1
Metallic Fe 0.5 - 10
Table 2 - Steel slag chemical composition
Physical Properties of Brick earth used :
The liquid limit of the sample = 29ml.
Plastic limit of soil = 24 %
Liquid limit of soil = 28 %
Plasticity Index IP = 4%
Specific gravity of soil = 2.35
Specific gravity of steel slag = 3.38
Maximum dry density = 2.268 g/cc
Optimum moisture content = 8%.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
METHODOLOGY
PROPERTIES OF MATERIALS USED
Brick Earth
Natural clay soil with fraction passing through the 4.75mm sieve and retained on 600
µm sieve was used and tested as per IS: 2386.Specific gravity 2.35.
Steel Slag
Steel slag in fine form is obtained from Agni steels Private Ltd, Ingur and its specific
gravity was found to be 3.38.
Water
STEEL SLAG FROM
AGNI STEELS (P )Ltd
CLAY MIXING WITH WATER SOIL
END PRODUCT - BRICKS
FIRING
DRYING
MOULDING
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Portable tap water available in the laboratory with pH value of 7.0±1 and confirming to
the requirements of IS: 456 - 2000 was used for mixing the brick earth.
WEIGHT VARIATION FOR PARTIAL REPLACEMENT OF BRICK EARTH IN
BRICKS BY STEEL SLAG
SL.NO PERCENTAGE OF REPLACEMENT OF
BRICK EARTH
DRY WEIGHT IN
(kg)
1 0% 2.955
2 10% 3.165
3 20% 3.265
4 30% 3.376
5 40% 3.510
6 50% 3.615
TESTS ON BRICKS
There are three standard tests for bricks as per IS – 3495:1992
COMPRESSIVE STRENGTH
WATER ABSORBTION
EFFLORESCENCE
COMPRESSIVE STRENGTH A compression – testing machine is used to find
out the compression strength of the brick. The compression plate of which shall have ball
seating in the form of a sphere the center of which coincides with the center of the plate shall
be used.
Place the specimen with flat face horizontal, and mortar filled face facing upwards
between two 3 – plywood sheets of 3mm thickness and carefully centered between plates of
the testing machine. Apply load axially at a uniform rate of 14N/mm2 (140kg/mm2) per
minute till failure occurs and note the maximum load at failure. The load at failure shall be the
maximum load at which the specimen fails to produce any further increase in the indicator
reading on testing machine.
Maximum load at failure in N
Compressive strength = ------------------------------------------
Average area of the bed faces in mm2
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
WATER ABSORPTION
A sensitive balance capable of weighting with in 0.1 % the mass of the specimen and a
ventilated oven is required to find out the percentage of water absorption.
The specimen is dried in ventilate oven at a temperature of 1050C to 115
0C till attains
substantially constant mass. The specimen is cooled to room temperature and obtain its weight
(W1) is obtained. Specimen warm to touch shall not be used for the purpose.
Completely dried specimen is immersed clean water at a temperature of 27+_ 2C for
24 hours. The specimen is removed and any traces of water are wiped out with damp cloth and
specimen is weighted. Complete the weighting 3 minutes after the specimen has been removed
from water (W2).
W2 - W1
Water absorption = ------------------- X 100
W2
EFFLORESCENCE
The brick is placed in water for 24 hours in the room temperature. Then the brick is
removed form the water after immersion of 24 hours. The brick is dried in the open area.
Whether the salt is deposited in the brick is nil, slight, moderate, or heavy is examined.
SL.NO
PERCENTAGE REPLACEMENT BY
SLAG
EFFLORESCENCE
1 0% NIL
2 10% NIL
3 20% NIL
4 30% NIL
5 40% NIL
6 50% NIL
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
RESULTS
COMPRESSIVE STRENGTH
S.NO PERCENTAGE OF REPLACEMENT
COMPRESSIVE
STRENGTH
in N / mm2
1 0% 4.1
2 10% 4.8
3 20% 5.5
4 30% 5.9
5 40% 6.7
6 50% 5.2
COMPRESSION TEST ON BRICKS
4.1 4.85.5 5.9
6.75.2
0
1
2
3
4
5
6
7
8
0% 10% 20% 30% 40% 50%
Replacement
Co
mp
ressiv
e S
tren
gth
(Mp
a)
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
WATER ABSORPTION
S.NO
PERCENTAGE OF REPLACEMENT
WATER ABSORPTION%
1 0% 16.38%
2 10% 13.28%
3 20% 12.95%
4 30% 12.85%
5 40% 11.40%
6 50% 12.80%
WATER ABSORPTION
16.413.3 12.95 12.85 11.4 12.8
0
5
10
15
20
0% 10% 20% 30% 40% 50%
% of Replacement
Wate
r ab
so
rpti
on
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
COST COMPARISON
SL.NO PERCENTAGE OF REPLACEMENT
COST
(Rs)
1 0% 2.60
2 10% 2.56
3 20% 2.52
4 30% 2.48
5 40% 2.44
6 50% 2.40
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
COST ESTIMATION
2.6
2.56
2.52
2.48
2.44
2.4
2.3
2.35
2.4
2.45
2.5
2.55
2.6
2.65
0% 10% 20% 30% 40% 50%
% OF REPLACEMENT
CO
ST
(Rs)
TECHNICAL COMPARISON ON STEEL SLAG BRICKS WITH CONVENTIONAL
BRICK AT OPTIMUM REPLACEMENT LEVEL (40%)
Specification Conventional
bricks Steel slag bricks
Advantage of steel slag
bricks
Compressive
Strength (Mpa) 4.1 6.7
Higher strength for
load bearing wall
Water absorption % 16.4% 11.4% Less water absorption
Hence more durability
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Dimensions
Length-190mm
Tolerance-6mm
Width-90mm
Tolerance-6mm
Height-90mm
Tolerance-6mm
Length-190mm
Tolerance-Nil
Width-90mm
Tolerance-Nil
Height-90mm
Tolerance-3mm
Quicker completion
lesser masonry
uniform shape
Wastage during
transit and storage More than-10% Max-5% Lower construction cost
Weight 3.0kg approx 3.5kg approx Strength is more
Air cracks More air cracks Less air cracks Beautiful plastered walls
DISCUSSIONS
The compressive strength of the brick increases as the percentage of replacement
increases up to 40 % of replacement. The optimum value of 6.7MPa (IS 1077-1972)was found
at a slag replacement proportion of 40% and after that any further replacement of slag
decreases the compressive strength.
The water absorption value of the brick decreases as the percentage of replacement
increases up to 40 % of replacement. The optimum value 11.4% (IS 1077-1972) was found at
slag replacement proportion of 40% and after that any further replacement of slag increase the
water absorption value. The efflorescence absorbed is NIL (IS 1077-1972) for all proportion
bricks.
CONCLUSIONS
From the above discussions it was found that the steel slag can be effectively used in
brick manufacturing in order to improve the compressive strength, water absorption and can be
effectively utilized as a replacement material for brick earth so that the following benefits can
be obtained.
Cost reduction
Social benefits &
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Mass utilization of waste material is possible by using steel slag in brick manufacturing
REFERENCES
(1) ―Assessment of human health and ecological risks posed by the uses of steel Industry
slags in the environment‖ – Deborah M. Proctor, Erinc, Shay, Kurt A. Fehling & Brent L.
Finley – Journal of Human Ecological and Risk Assessment, Vol.8,Issue 4, pp.681-711, 2002.
(2) National Slag Association, Environmental Technical Bulletin, May 26, 2003
(3) National Slag Association, Environmental Technical Bulletin, November , 1998 -
John L. Wintenborn & Joseph J. GreenCollier on behalf of The Steel Slag Coalition,
Shannon, Rill & Scott, PPLC.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
STUDY ON FLY ASH BASED GEO-POLYMER CONCRETE.
Ms.C.Chella Gifta,
Lecturer
Department of Civil Engineering.
St.Peter’s Engineering College, Chennai 54.
ABSTRACT
Concrete usage around the globe is second only to water. An important ingredient
in the conventional concrete is the Portland cement. The production of one ton of cement
emits approximately one ton of carbon dioxide to the atmosphere. Moreover, cement
production is not only highly energy intensive, next to steel and aluminium, but also
consumes significant amount of natural resources. In order to meet infrastructure
developments, the usage of concrete is on the increase. Fly ash –based Geopolymer
concrete has excellent compressive strength .It can be used in many infrastructure
applications. One ton of fly ash can be utilised to produce about 2.5 meters of high
quality Geopolymer concrete, and the bulk cost of chemicals needed to manufacture this
concrete is cheaper than bulk cost of one ton of Portland cement. This paper deals with
the research work carried out on Fly ash based Geopolymer concrete. The fly ash
obtained from Ennore thermal Power station is used to make test specimens. From the
results of the experimental investigations it was concluded that the Geopolymer concrete
has great potential for use in Civil Engineering applications. It is discovered that a great
amount of reduction is obtained in Co2 emissions. And also it is concluded that higher
concentration of polymers results in higher compressive strength.
GENERAL
Ordinary Portland cement (OPC) is conventionally used as a primary binder to
produce concrete. The environmental issues associated with the production of OPC are
well known. The amount of carbon dioxide released during the manufacture of OPC due
to the calcinations of limestone and combustion of fossil fuel is in the order of one ton of
OPC produced. On the other hand, the abundant availability of fly ash worldwide creates
opportunity to utilise this by-product of burning coal, as a substitute for OPC to
manufacture concrete. When used as a partial replacement of OPC, in the presence of
water and in ambient temperature, fly ash reacts with the calcium hydroxide during the
hydration process of OPC to form Calcium Silicate
(C-S-H) gel. The development and application of high volume fly ash concrete, which
enabled the replacement of OPC up to 60% by mass is a significant development.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
FLY ASH-BASED GEOPOLYMER CONCRETE
In this research work, fly ash based Geopolymer is used as the binder, instead of
Portland or other hydraulic cement paste, to produce concrete. The fly ash- based
Geopolymer paste binds the loose coarse aggregates, fine aggregates and other un-reacted
materials together to form the Geopolymer Concrete, with or without the presence of
admixtures. The manufacture of Geopolymer Concrete is carried out using the usual
methods of concrete technology.
As in the case of OPC concrete, the aggregates occupy about 75-80% by mass, in
Geopolymer Concrete. The silicon and the aluminium in the fly ash react with an alkaline
liquid that is a combination of sodium silicate and sodium hydroxide solutions to form
the Geopolymer paste that binds the aggregates and other un-reacted materials.
The main objectives of this work are:
1. To use fly ash based Geopolymer as the binder, instead of Portland cement paste, to
produce concrete.
2. To develop a concrete mix to produce fly ash based Geopolymer Concrete.
3. To study the Compressive Strength and effect of curing temperature of fly ash based
Geopolymer Concrete.
Constituents of Geopolymer
Source Materials
Any material that contains mostly Silicon (Si) and Aluminium (Al) in amorphous form is
a possible source material for the manufacture of Geopolymer. Several minerals and
industrial by-product materials have been investigated in the past. Metakaolin or calcined
kaolin (Davidovits; Barbosa et al), low-calcium ASTM class F fly ash (Palomo et al),
natural Al-Si minerals(Xu and van Deventer), combination of calcined mineral and non-
calcined minerals (Xu and van Deventer), combination of fly ash and metakaolin (van
Jaarsveld et al.), and combination of granulated blast furnace slag and metakaolin have
been studied as source materials.
Metakaolin is preferred by the niche Geopolymer product developers due to its
high rate of dissolution in the reactant solution, easier control on the Si/Al ratio and the
white colour,but for making concrete in a mass production state, metakaolin is expensive.
Low-calcium (ASTM Class F) fly ash is preferred as a source material than high-
calcium (ASTM Class C) fly ash. The presence of calcium in high amount may interfere
with the polymerization process and alter the microstructure.
Davidovits calcined kaolin clay for 6 hours at 750ºC. He termed this metakaolin
as KANDOXI (KAolinite, Nacrite, Dickite OXIde), and used it to make geopolymers.
For the purpose of making Geopolymer concrete, he suggested that the molar ratio of Si-
to-Al of the material should be about 2.0
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Natural Al-Si minerals have shown the potential to be the source materials for
Geopolymerisation, although quantitative prediction on the suitability of the specific
mineral as the source material is still not available, due to the complexity of the reaction
mechanisms involved (Xu and van Deventer). Among the by-product materials, only fly
ash and slag have been proved to be the potential source materials for making
Geopolymers. Fly ash is considered to be advantageous due to its high reactivity that
comes from its finer particle size than slag. Moreover, low-calcium fly ash is more
desirable than slag for Geopolymer feedstock material.
The suitability of various types of fly ash as Geopolymer source material has been
studied by Fernandez-Jimenez and Palomo. These researchers claimed that to produce
optimal binding properties, the low-calcium fly ash should have the percentage of
unburnt material (LOI) less than 5%, Fe2O3 content should not exceed 10%, and low CaO
content, the content of reactive silica should be between 40-50%, and 80-90% of particles
should be smaller than 45 µm. On the contrary, van Jaarsveld et al found that fly ash with
higher amount of CaO produced higher compressive strength, due to the formation of
calcium-aluminate-hydrate and other calcium compounds, especially in the early ages.
The other characteristics that influenced the suitability of fly ash to be a source material
for Geopolymers are the particle size, amorphous content, as well as morphology and the
origin of fly ash.
Alkaline Liquids
The most common alkaline liquid used in Geopolymerisation is a combination of
sodium hydroxide (NaOH) or potassium hydroxide (KOH) and sodium silicate or
potassium silicate .The use of a single alkaline activator has been reported by Palomo et
al concluded that the type of alkaline liquid plays an important role in the polymerization
process. Xu and van Deventer confirmed that the addition of sodium silicate solution to
the sodium hydroxide solution as the alkaline liquid enhanced the reaction between the
source material and the solution.
Mixture Proportions
Most of the reported works on Geopolymer material to date were related to the
properties of Geopolymer paste or mortar, measured by using small size specimens. In
addition, the complete details of the mixture compositions of the Geopolymer paste were
not reported.
Palomo et al studied the Geopolymerisation of low-calcium ASTM Class F fly ash (molar
Si/Al=1.81) using four different solutions with the solution-to-fly ash ratio by mass of
0.25 to 0.30. The molar SiO2/K2O or SiO2/Na2O of the solutions was in the range of 0.63
to 1.23. The specimens were 10x10x60 mm in size. The best compressive strength
obtained was more than 60 MPa for mixtures that used a combination of Sodium
hydroxide and Sodium silicate solution, after curing the specimens for 24 hours at 65˚C.
On the other hand, van Jaarsveld et al reported the use of the mass ratio of the solution to
the powder of about 0.39. In their work, 57% fly ash was mixed with 15% kaolin or
calcined kaolin. The alkaline liquid comprised 3.5% sodium silicate, 20% water and 4%
sodium or potassium hydroxide. In this case, they used specimen size of 50x50x50 mm.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
The maximum compressive strength obtained was 75 MPa when fly ash and buiders‘
waste were used as the source material.
Fresh Geopolymers and Manufacturing Process
Only limited information on the behaviour of the fresh Geopolymers has been
reported. Using metakaolin as the source material, it was found that the fresh
Geopolymer mortar became very stiff and dry while mixing, and exhibited high viscosity
and cohesive nature. They suggested that the forced mixer type should be used in mixing
the Geopolymer materials, instead of the gravity type mixer. An increase in the mixing
time increased the temperature of the fresh Geopolymers, and hence reduced the
workability. To improve the workability, they suggested the use of admixtures to reduce
the viscosity and cohesion.
However, curing temperature and curing time have been reported to play important roles
in determining the properties of the Geopolymer materials made from by-product
materials such as fly ash. Palomo et al stated that increase in curing temperature resulted
in higher compressive strength.
Factors affecting the Properties of Geopolymers
Curing temperature, water content, CaO content, water-to-fly ash ratio, molar
composition of the oxides present in the mixture, molar Si-to-Al ratio in the source
material, type of alkali liquid, dissolution of Si, and the molar Si-to-Al ratio in solution
are the factors identified as important parameters affecting the properties of
Geopolymers.
Geopolymer Concrete Products
Palomo et al reported the manufacture of fly ash-based Geopolymer concrete
railway sleepers. Earlier, Balaguru et al reported the use of Geopolymer composites to
strengthened concrete structures as well as Geopolymer coating to protect transportation
infrastructures.. The performance of Geopolymers was better than the organic polymers
in terms of fire resistance, durability under ultra violet light, and did not involve any toxic
substances. In that study, Geopolymers with the Si/Al ratio of more than 30 was used.
Application of Geopolymers
Geopolymers can be used for several applications as given below.
Bricks, ceramics, fire protection
Low CO2 cement, concrete, radioactive & toxic waste encapsulation
Heat resistance composites, foundry equipments, fibre glass composites
Sealants for industry
Fire resistance and heat resistance fibre composites
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
EXPERIMENTAL PROGRAM
In this research work investigations were directed towards the development of the
process of making fly ash-based Geopolymer Concrete.
The focus of the study was to identify the salient parameters that influence the
mixture proportions. As far as possible, the current practice used in the manufacture and
testing of ordinary Portland cement (OPC) concrete was followed. The aim of this action
was to ease the promotion of this ‗new‘ material to the concrete construction industry. In
order to simplify the development process; the compressive strength was selected as the
benchmark parameter. This is not unusual because compressive strength has an intrinsic
importance in the structural design of concrete structures and many other mechanical
properties of concrete can be related to the compressive strength. Although Geopolymer
concrete can be made using various source materials, the present study used only dry fly
ash. Also, as in the case of OPC, the aggregates occupied 75-80 % of the total mass of
concrete. In order to minimize the effect of the properties of the aggregates on the
properties of fly ash-based Geopolymer, the study used aggregates from only one source.
Fly Ash
In the present experimental work, low-calcium, Class F, dry fly ash obtained from
the silos of Ennore Thermal Power Station in Tamil Nadu was used as the base material.
It is refractory and alkaline in nature, having fineness in the range of 3000-6000
sq.cm/gm. The molar Si-Al ratio was about 2 and the calcium oxide content was very low
when compared to the iron oxide (Fe2O3) content. The colour was dark grey.
Alkaline Liquid
A combination of sodium silicate solution and sodium hydroxide solution was
chosen as the alkaline liquid. Sodium-based solutions were chosen because they were
cheaper than Potassium-based solutions. The sodium hydroxide solids were either a
technical grade in flakes or pellets.
The sodium hydroxide (NaOH) solution was prepared by dissolving either the
flakes or pellets in water. The mass of NaOH solids in a solution varied depending on the
concentration of the sodium expressed in terms of molar, M. For instance, NaOH
solution with a concentration of 8M consisted of 8 x 40 = 320 grams of NaOH solids (in
flake or pellets form) per litre of the solution, where 40 is the molecular weight of NaOH.
The chemical composition of sodium silicate solution was Na2O = 8.5%, SiO2= 28% and
water 62.5% by mass.
Aggregates
Both coarse and fine aggregates were used. In this, there are three combinations
of coarse aggregates are used of various sizes namely 20mm, 12mm and 7mm. Coarse
and fine aggregates are obtained from local sources. Different sizes of aggregates are
used in this work to facilitate uniform grading and to minimise voids in the concrete
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Mixing
It was found that the fresh fly ash-based Geopolymer concrete was grey in colour
(due to the grey colour of the fly ash), and was cohesive. The amount of water in the
mixture played an important role on the behaviour of fresh concrete and segregation of
aggregates, and the paste occurred of hardened concrete.
Davidovits (2002) suggested that it is preferable to mix the sodium silicate solution and
the sodium hydroxide solution together at least one day before adding the liquid to the
solid constituents. He also suggested that the sodium silicate solution obtained from the
market is usually in the form of a dimmer or a trimer, instead of a monomer, and mixing
it together with the sodium hydroxide solution assists the polymerization process. When
this suggestion was followed, it was found that the occurrence of bleeding and
segregation ceased. The effects of water content in the mixture and the mixing time were
identified as test parameters to observe the following standard process of mixing in all
further studies.
Curing
Geopolymer concrete specimens should be wrapped during curing at elevated
temperatures in a dry environment (in the oven) to prevent excessive evaporation. Unlike
the small Geopolymer paste specimens, which can easily be wrapped by placing a lid on
the mould, a suitable method was needed for large size Geopolymer concrete specimens.
Extensive trials revealed that concrete specimens by using vacuum bagging film is
effective for temperature up to 100°C for several days or a twist tie wire was utilized. The
later was used in all further experimental work due to its simplicity and economics.
Fig1: Concrete specimens after wrapping
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
MIX PROPORTION
Based on the past research on Geopolymer pastes available in the literature and the
experience gained during the preliminary experimental work, the following ranges were
selected for the constituents of the mixture used in further studies described below:
Dry fly ash
Alkaline liquid
Ratio of sodium silicate solution-to- sodium hydroxide solution, by mass:
0.4 to 2.5. This was fixed at 2.5 .Molarity of sodium hydroxide (NaOH)
solution in the range of 8M to 16M.Ratio of activator solution-to-fly ash,
by mass, in the range of 0.3 and 0.4.
Coarse and fine aggregates, of approximately 75% to 80% of the entire mixture
by mass. This value is similar to that used in OPC concrete.
Super plasticizer, in the range of 0% to 2% of fly ash, by mass.
Extra water, when added, in mass.
MIXING, CASTING AND CURING
The aggregates were prepared in saturated-surface-dry condition, and were kept in
plastic buckets with lid. The solid constituents of fly ash-based Geopolymer concrete, i.e.
the aggregates and fly ash, were dry mixed. The liquid part of the mixture, i.e. sodium
hydroxide and sodium silicate solution, added water (if any) were premixed and then
added to the solids. The wet mixing was usually continued.
The fresh fly ash-based Geopolymer concrete was grey in colour and shiny in
appearance. The mixtures were usually cohesive. Compaction of fresh concrete in the
cubical steel moulds was achieved by applying 25 manual strokes per layer in three equal
layers. After casting, the specimens were covered using vacuum bagging film.
Curing was done both at room temperature and elevated temperature. Curing at
high temperature (60˚C) for 24 hours was done with the help of laboratory oven. Figure
3.9 shows the curing process at elevated temperature in laboratory oven.
COMPRESSIVE STRENGTH TEST
The compressive strength tests on hardened fly ash-based Geopolymer concrete
were performed using a 1000 kN capacity compression testing machine. Four 150x150
mm concrete cubes were tested for every lot. The results are given in various Figures and
Tables.
EXPERIMENTAL RESULTS AND DICUSSION
Each of the compressive strength test data plotted in Figures or given in Tables
corresponds to the mean value of the compressive strength of four test cubes in a series.
The details of Geopolymer concrete mixtures used in the present study are given
in Table 1. The type of curing for each mix is also given in the Table. Totally four
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
mixtures were used for study. The molarity for the alkaline solution and curing
temperature were varied for the different mixtures as shown in Table 1.
The effects of various salient parameters on the compressive strength of fly ash-based
Geopolymer concrete are also discussed. The parameters considered are as follows:
1. Concentration of sodium hydroxide (NaOH) solution, in Molar
2. Curing temperature
3. Age of concrete
Table 1: Details of Mixtures
Mix
No
Aggregate Fly ash
(kg)
NaOH Solution
Sodium
Silicate
(kg)
Curing
Temperature 20mm
(kg)
12 mm
(kg)
7 mm
(kg)
Fine
sand
(kg)
Mass
(kg) Molarity
1 277 370 647 554 476 74 8 M 184 Room Temp.
2 277 370 647 554 476 74 8 M 184 60˚C
3 277 370 647 554 476 74 14 M 184 Room Temp.
4 277 370 647 554 476 74 14 M 184 60˚C
Table 2: Compressive strength of concrete after 7 days and 28days for Mix 1 at
room temperature
Concrete
Specimen
No.
Size
(mm)
7 daysCompressive
strength
(MPa)
28 daysCompressive
strength
(MPa)
1 150 x 150 x 150 11.02 14.67
2 150 x 150 x 150 10.44 14
3 150 x 150 x 150 10.8 13.77
4 150 x 150 x 150 10 14.67
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Tables 2 give the compressive strength at 7 days and 28 days for Design Mix 1 with
curing at room temperature. The average compressive strength was 10.57 MPa at 7 days
and 14.28 MPa at 28 days. The increase in compressive strength of concrete was 26 %.
Table 3 Compressive strength of concrete after 7 days and28 days for Mix 2 at
elevated temperature (60˚C)
Concrete
Specimen
No.
Size
(mm)
7daysCompressive
strength
(MPa)
28 daysCompressive strength
(MPa)
1 150 x 150 x 150 26.88 29.33
2 150 x 150 x 150 26.44 29.11
3 150 x 150 x 150 25.77 28.44
4 150 x 150 x 150 26.66 28.44
Tables 3 give the compressive strength at 7 days and 28 days for Design Mix 2 with
curing at elevated temperature (60˚C). The average compressive strength was 26.44 MPa
at 7 days and 29.05 MPa at 28 days. The increase in compressive strength of concrete
was 9 %.
Table 4: Compressive strength of concrete after 7 days and 28days for Mix 3 at
room temperature
Concrete
Specimen No.
Size
(mm)
7days Compressive
strength
(MPa)
28daysCompressive
strength
(MPa)
1 150 x 150 x 150 15.55 17.55
2 150 x 150 x 150 14.66 17.33
3 150 x 150 x 150 15.55 17.11
4 150 x 150 x 150 15.33 17.55
Tables 4 gives the compressive strength at 7 days and 28 days for Design Mix 3 with
curing at room temperature. The average compressive strength was 15.27 MPa at 7 days
and 17.38 MPa at 28 days. The increase in compressive strength of concrete was 12.14
%.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Table 5: Compressive strength of concrete after 7 days and 28days for Mix 4 at
elevated temperature (60˚C)
Concrete
Specimen
No.
Size
(mm)
7daysCompressive
Strength
(MPa)
28daysCompressive
strength
(MPa)
1 150 x 150 x 150 34.22 36.22
2 150 x 150 x 150 33.77 36.44
3 150 x 150 x 150 34.22 36
4 150 x 150 x 150 34.44 36.22
Tables 5 give the compressive strength at 7 days and 28 days for Design Mix 4 with
curing at elevated temperature (60˚C). The average compressive strength was 34.16 MPa
at 7 days and 36.22 MPa at 28 days. The increase in compressive strength of concrete
was 5.68 %.
GRAPHICAL COMPARISON OFCOMPRESSIVETEST RESULTS
12
34
7
280
5
10
15
20
25
30
35
40
Compressive
Strength (MPa)
Mixture No.
Age of Test (days)
7
28
EFFECT OF SALIENT PARAMETERS
Concentration of Sodium hydroxide (NaOH) Solution
Mixtures 1 to 4 were made to study the effect of concentration of sodium hydroxide
solution on the compressive strength of concrete. The test specimens were cured at room
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
temperature and elevated temperatures according to the schedule. The measured 7th day
and 28th
day compressive strengths of test specimens are given in Table 6 and Figure 2.
Table 6: Effect of Alkaline Solutions
Mix
Concentratio
n of NaOH (
in Molars)
Ratio of
Sodium
silicate to
NaOH
solution (by
mass)
Curing
Temperature
Average Compressive
strength
At 7th day
(MPa)
At 28th
day
(MPa)
1 8M 2.5 Room
temperature 10.57 14.28
2 8M 2.5 60˚C 26.44 29.05
3 14M 2.5 Room
temperature 15.27 17.38
4 14M 2.5 60˚C 34.16 36.22
The study revealed that the increase in compressive strength of concrete at room
temperature is 30.77 % and 22.59 % at 60˚C at 7 days for change in concentration from
8M to 14M of NaOH.
.
Fig 2: Effect of Concentration of Sodium hydroxide solution
Curing temperature
Fig 3 shows the effect of curing temperature on the compressive strength for mixtures 1
to 4 after curing at room temperature and elevated temperature (60˚C) respectively.
Higher curing temperature results in larger compressive strength. Curing was performed
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
in an oven for 24 hours in case of mixtures 2 and 4 while the other mixtures are left in
room temperature in laboratory.
Fig 3: Effect of Curing Temperature for Mix 1 and 2 & Mix 3 and 4
Age of Concrete
Fig 4 shows the effect of age of concrete on the compressive strength. The test specimens
were prepared using mixtures 1 and 3 cured at room temperature while mixtures 2 and 4
cured at elevated temperatures (60˚C) for 24 hours. Because the chemical reaction of
heat-cured Geopolymer concrete is due to substantially fast polymerisation process, the
compressive strength increased slightly with the age of concrete by 19.07 % and 7.34 %
with respect to the curing temperature. This observation is in contrast to the well-known
behaviour of OPC concrete, which undergoes hydration process and hence gains strength
over time. The compressive strength of the specimens was tested at 7th and 28
th day after
the date of casting.
Fig 4. Compressive Strength of concrete at different ages for Design Mixes 1 and 2 &
Mixes 3 and 4
CONCLUSIONS
Based on the carried out experimental work on Geopolymer concrete, the following
conclusions are made:
1. The production of cement is increasing about 3% annually. The production of one
tone of cement liberates about one tone of CO2 to the atmosphere. It is suggested
that the amount of CO2 emissions by the cement industries can be reduced by
using Geopolymer concrete.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
2. Huge volumes of fly ash are generated around the world. Most of the fly ash is
not effectively used, and a large part of it is disposed in landfills. In this work, the
unused fly ash is used to produce the valuable concrete material.
3. Higher concentration (in terms of molar) of sodium hydroxide solution results in
higher compressive strength of fly ash-based Geopolymer concrete.
4. As the curing temperature is increased to 60˚C, the compressive strength of fly-
based Geopolymer concrete also increased.
5. The compressive strength of heat-cured fly ash-based Geopolymer concrete does
not depend on age as the specimens attained its maximum strength in 7 days
itself.
6. The normal water curing needed for the hydration process in OPC concrete is not
needed in this case as the process deals with polymerisation process and the
curing time is greatly reduced which facilitates the concrete to be used after 7
days.
7. Geopolymer concrete has great potential for use in civil engineering applications.
Further studies are required on various properties of Geopolymer Concrete and
structural members to prepare necessary guidelines for its use.
8.
REFERENCES
1. Barbosa.V.F.F, (2000). ―Synthesis and Characterisation of Materials Based on
Inorganic Polymers of Alumina and Silica: Sodium Po lysialate
Polymers‖ .International Journal of Inorganic Materials 2(4): 309-317.
2. Davidovits, J . (2002). Perso na l Co mmunicat io n o n t he Process o f
Mak ing o f Geopolymer Concrete.383-397
3. Malhotra, V. M.(2002). "High-Performance High-Volume Fly Ash Concrete."
ACI Concrete International 24(7): 1-5.
4. McCaffrey, R. (2002). "Climate Change and the Cement Industry." Global
Cement and Lime Magazine (Environmental Special Issue):
15-19.
5. Mehta, P.K. (2001)."Reducing the Environmental Impact of Concrete."
ACI Concrete International 23(10): 61-66.
6. Palomo,A., A.Fernandez-Jimenez, C.Lopez-Hombrados, J.L.Lleyda (2004).
Precast Elements Made of Alkali-Activated Fly Ash Concrete. 1323-1329
7. van Jaarsveld, J. G. S.,(1997). "The Potential Use of Geopolymeric Materials to
Immobilise Toxic Metals: Part I. Theory and Applications." Minerals Engineering
10(7): 659-669.
8. Xu, H. and J.S.J.van Deventer (2002). "Geopolymerisation of Multiple
Minerals."Minerals Engineering 15(12): 1131-1139.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
DESIGN OF COLD-FORMED STEEL PLAIN CHANNELS
S.Manjuladevi1
1Lecturer, Department of Civil Engineering
Sathyabama University, Chennai
ABSTRACT
This paper gives an overview of the design procedures formulated for plain
channels. These formulations are based on experimental and finite element studies. The
scope of the work covers laterally braced beams, columns and beam-columns of cross-
sections in the range of practical applications by the industry. The recommendations treat
members that are made up of elements that may be in the post-buckling or post yielding
range.
Key Words: cold-formed steel; plain channels; design; effective width
INTRODUCTION
Cold-formed steel plain channels shown in Figure1 are used in several
applications such as bracing members in racks and tracks in steel framed housing. This
paper gives an overview of the design procedures developed for laterally braced beams,
columns and beam-columns of plain channels. Current design procedures were found to
be inaccurate.
The design procedures developed are applicable to cross-sections in the range of practical
sections used in the industry, namely 1/ 12 bb . The design procedures developed are
consistent with AISI Specification for calculating the overall capacity of plain channels.
ELASTIC BUCKLING
The determination of the ultimate strength when the plate elements are in the post
buckling range is based on the effective width procedure. The effective width procedure
necessitates the use of the plate buckling stress or the plate buckling coefficient k.
Simple equations for plate buckling coefficient k considering the interaction between
plate elements were developed for minor and major axis bending as well as for columns.
These equations were obtained by using a computer program CUFSM developed by
Schafer (1997) at Cornell University. The dimensions of plain channels are in the ranges
of practical applications by the industry. Below is a list of these equations.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Minor Axis Bending with Stiffened Element in Tension (Figure 2)
2555.1)(1451.01
2 b
bk f
Minor Axis Bending with Stiffened Element in Compression (Figure 3)
2064.0)(5345.6)(5119.41
22
1
2 b
b
b
bk f
fw kbbk 2
21 )/(
Figure 2
Figure 3
Figure 1 Plain Channel
flange
b1
b
2
1
web
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
1329.0)(2346.41
2 b
bk f , when 2264.0
1
2 b
b
7452.0)(3561.01
2 b
bk f , when 2264.0
1
2 b
b
Major Axis Bending with Unstiffened Element in Uniform Compression
Type a (Figure 4)
fw kbbk 2
21 )/(
Type b (Figure 5)
1246.1)(0348.01
2 b
bk f
Figure 4
Figure 5
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
fw kbbk 2
21 )/(
Columns (Figure 6)
0237.0)(2851.11
2 b
bk f , when 7201.0
1
2 b
b
8617.0)(0556.01
2 b
bk f , when 7201.0
1
2 b
b
ULTIMATE STRENGTH
The formulations developed involve the use of effective widths for the component
plate elements that are in the post-buckling. Using these effective widths effective section
properties and hence the ultimate load carrying capacities are determined. The approach
is thus in agreement with the frame work of the unified approach of Pekoz (1987) used in
the AISI Specification (1996).
For members that exhibit inelastic reserve capacity, post yield strain reserve capacity
expressed in terms of a ratio, Cy that is the ratio ultimate strain divided by the yield strain.
The ultimate moment of a flexural member is determined by statics based on the ultimate
strain capacity as is done in the AISI Specification (1996). The details of the equations
developed are given below.
MINOR AXIS BENDING WITH STIFFENED ELEMENT IN TENSION
Effective Width Model for Flanges
fy Ekftb /)/(052.1 2 or cry ff /
2555.1)/(1451.0 12 bbk f
if 8590
9.31
925.0
y
cr
ff
if 8590
Figure 6
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
f2
f1
b1o
b2o
1
2bbe
eyns SfM
Post-yield Strain Reserve Capacity Model
Cy = 3.0 for 5350
Cy = 20924058770
for 85905350
Cy = 1 for 859.0
The nominal moment capacity is determined as described in AISI Specification
(1996) Section C3.1.1 b.
MINOR AXIS BENDING WITH STIFFENED ELEMENT IN COMPRESSION
Effective Width Model
For stiffened elements in uniform compression:
The effective width, b, is to be determined using AISI Specification Section B2.1
yFf , wk k . The value of wk is to be determined by the equations given above.
For unstiffened elements under a stress gradient:
For the post-buckling behavior of unstiffened elements a consistent effective
width shown in Figure 7 as suggested by Schafer (1997) is used.
When 1
2
f
f ,
)1(1
bb o
2))1(
( 2
2bb o
where
77.00 30.0
95.077.0 23.0
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Figure 7
00.195.0 6.46.4
in which,
1 when 673.0
)/22.01( when 673.0
crf
f1
eyns SFM
When unstiffened elements does not undergo local buckling, the nominal moment
capacity is determined based on initiation of yielding or its ultimate moment. The
ultimate is determined based on the ultimate (post-yield) strain capacity.
Post-yield Strain Capacity Model
Cy=3 for 46.0
Cy= )46.0673.0()46.0(
*23
for 673.046.0
Cy=1 for 673.0
The nominal moment capacity is determined as described in AISI Specification
(1996) Section C3.1.1 b.
MAJOR AXIS BENDING
For unstiffened element in uniform compression, the effective widths are
determined as described in AISI Specification Section B3.2 with yFf , and using
the plate buckling coefficient as given above, namely k= kf
For stiffened element under a stress gradient, the consistent effective width described
above is used and eyns SFM .
FLAT-ENDED AND PIN-ENDED COLUMNS
Flat-ended columns: as the shift of the line of action of the internal forces caused by
local buckling deformations does not induce overall bending in flat-ended columns,
column equation can be used to design flat-ended columns.
Pin-ended columns: as the shift of neutral axis caused by local buckling is
significant in overall bending of pin-ended columns, beam-column equation can be
used to design pin-ended columns. Two thirds of the maximum eccentricity is
selected for the beam-column equation because the eccentricity varies along the
length of the column.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
BEAM-COLUMNS
Strength of plain channel beam columns can be determined by the interaction
equations (AISI Specification Section C5.2.2) with the improved plate buckling
coefficient k described above.
The parameters for the column part of the beam-column equations, flat-ended columns
are to be treated as concentrically loaded columns; while pin-ended columns are treated
as beam-columns. The eccentricity of the load should be determined on the basis of the
location of the load and the average deflections of the beam column instead of the
maximum deflections. The parameters for the beam part of the beam-column equations,
the formulations developed above are to be used.
COMPARISON STUDIES
The experimental results of several studies were first evaluated by finite element
approaches as to their validity. Some of the test results were not reliable due to some
deficiencies in the tests. The finite element studies indicated which test results should be
excluded from further evaluation.
Minor Axis Bending with Stiffened Element in Tension
Experimental result of El Mahi and Rhodes (1985), Enjiky (1985), Jayabalan (1989),
and the tests carried out at Cornell University in 1999 by Fang Yiu and Teoman Pekoz
were used to formulate the provisions for the case of minor axis bending with stiffened
element in tension.
The mean value of Mns over Mtest ratio (excluding the results for plain channels where the
flanges are not at right angles to the web) is 0.993; the sample standard deviation is
0.114; resistance factor is 0.718 in probability model. For specimens with post-yield
reserve capacity, that is, Cy>1, is 0.690; When Cy=1, is 0.740. The comparison
results are shown in Figure 8.
Minor Axis Bending with Stiffened Element in Compression
Test results of Enjiky (1985) are used for minor axis bending with stiffened element
in compression. Comparison in Figure 8 shows that the mean value of Mns over Mtest ratio
is 1.038; the sample standard deviation is 0.087; resistance factor = 0.769 in probability
model. The comparison results are shown in Figure 9.
Major Axis Bending with Unstiffened Elements in Uniform Compression
Test results of Reck reported by Kalyanaraman (1976) and Talja (1992) provided the
basis for the design procedure. For the relevant test data from these references the mean
value of Mns over Mtest ratio is 0.956 and the sample standard deviation is 0.080. The
comparison results are shown in Figure 10.
Flat-ended Columns Data from Talja (1990), Young (1997), Mulligan & Pekoz (1983) provided the
basis for the procedures for flat-ended columns. The mean value of Mns over Mtest ratio
for the data is 0.950; the sample standard deviation is 0.126; resistance factor is 0.670
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
in probability model for fixed-ended columns. The results are illustrated in Figure 11.
Pin-ended Columns
Test results from Young (1997) for two series of pin-ended column test Series
P36 and P48 were used in the development of the design procedures. The mean value of
Mns over Mtest ratio is 0.920; the sample standard deviation is 0.078; resistance factor is
0.675 in probability model. The results are illustrated in Figure 12.
Beam – Columns
Jayabalan (1989) and Srinivasa (1998) provide results of beam-column experiments
with eccentricity of the load in the plane of symmetry. Fang Yiu and Pekoz in 2000 tested
beam-column with eccentricity of the load in the plane of asymmetry. Only the data
corresponding to practical cross-sections are evaluated and plotted in Figure 13.
The correlation of the test results of C, channel, and hat section beam-columns with the
use of interaction equations was plotted in Figure 7.3-1 of Pekoz (1987). This figure
presented the results of all the tests with loads with uniaxial or biaxial eccentricities. Rp,
Rx and Ry represent the first, second and the third terms of the AISI interaction equation.
Ro equals 0.707(Rx+Ry). The projections of test points on the Rp-Ro plane was plotted.
The results that fell outside of the solid line in the Figure 12 on the right indicated that the
interaction equation is conservative for those cases. Results from Jayabalan (1989) and
Srinivasa (1998) and Fang Yiu and Pekoz are added to the Pekoz (1987) figure and given
in Figure 13. It is seen that the interaction equation is also conservative for plain channel
section.
CONCLUSION
Design recommendations for calculating the overall capacity of plain channel
sections in the range of practical applications by the industry are presented. Comparison
studies indicate good agreement with experimental results.
REFERENCES:
1. American Iron and Steel Institute (1996). AISI Specification for the Design of
Cold Formed Steel Structural Members. American Iron and Steel Institute.
Washington, D.C.
2. Ben Young (1997). ―The Behavior and Design of Cold-formed Channel
Columns‖, Ph. D Dissertation, Dept. Of Civil Engineering, University of Sydney,
Australia
3. El Mahi, A. (1985). ―Behavior of Unstiffened Elements in Bending‖, M. S.
Thesis, Dept. Of Mechanics of Materials, University of Strathclyde, Glasgow, UK
4. Enjily, Vahik (1985). "The Inelastic Post Buckling Behavior of Cold-Formed
Sections", Ph.D Dissertation, Dept. of Civil Engineering, Building and
Cartography, Oxford Polytechnic, UK
5. Jayabalan, P. (1989). " Behavior of Non-Uniformly Compressed Thin Unstiffened
Elements", Ph.D Dissertation, Dept. of Civil Engineering, India Institute of
Technology, Madras
6. Kalyanaraman, Venkatakrishnan (1976). " Elastic and Inelastic Local Buckling
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
and Postbuckling Behavior of Unstiffened Compression Elements", Ph.D
Dissertation, Dept. Of Civil Engineering, Cornell University, USA
7. Mulligan, G. P. and Pekoz, T. (1983). The Influence of local Buckling on the
Structural Behavior of Singly-Symmetric Cold-Formed Steel Columns. Ph.D.
Thesis, Cornell University, Ithaca, NY.
8. Pekoz, Teoman(1987). Development of a Unified Approach to the Design of
Cold-Formed Steel Members
9. Rao, K. Srinivasa (1998), " Coupled Local and Torsional-Flexural Buckling of
Cold-Formed Steel Members", Ph.D Dissertation, Dept. of Civil Engineering,
India Institute of Technology, Madras
10. Rhodes, J. (1985). ―Final Report on Unstiffened Elements‖, University of
Strathclyde, Glasgow, UK
11. Schafer, B.W. (1997). Cold-Formed Steel Behavior and Design: Analytical and
Numerical Modeling of Elements and Members with Longitudinal Stiffeners.
Ph.D. Thesis, Cornell University, Ithaca, NY.
12. Talja, Asko (1990). "Design of the Buckling Resistance of Compressed HSS
Channels", Research Note 1163, Technical Research Centre of Finland
13. Talja, Asko (1992). "Design of Cold-Formed HSS Channels for Bending and
Eccentric Compression", Research Note 1403, Technical Research Centre of
Finland
NOTATION:
E = Modulus of Elasticity
= Poisson's ratio
G = )1(2
E = Shear Modulus
t = plate thickness
D = )1(12 2
3
Et = plate rigidity
1b = Depth of web element
2b = Width of flange element
yf = yield stress
crf = critical buckling stress of the cross-section
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
fk = plate buckling coefficients considering interaction of plate elements in terms of
flange width
wk = plate buckling coefficients considering interaction of plate elements in terms of web
depth
= post-buckling reduction factor
= slenderness factor
nsM = nominal moment capacity
eS = elastic section modulus of the effective section
yC = compression strain factor
1f = maximum compressive (+) stress on an element under a stress gradient
2f = tension (-) stress for an element under a stress gradient
1
2
f
f
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
EFFECT OF THICKNESS OF SHEET IN BEHAVIOUR OF
HOLLOW COLDFORMED STEEL CONCRETE COMPOSITE
COLUMN USING SELF COMPACTING CONCRETE
N.K.Amudhavalli 1, N.Balasubramaniam
2, Dr.R.Thenmozhi
3 &
Dr.M.K.Saseetharan 4
1. Lecturer of TCE College, Karumathampatti,
2.Principal of Ramakrishna Polytechnic college,
3.Asst Professor in structural Engineering,
4. Professor, Dept of Civil Engg, GCT, Coimbatore.
ABSTRACT
Considering the performance of the existing structures, the parameters that need
more attention are two things:
1. Strength and Ductility as for as the steel structures are concerned.
2. Density and Compaction as for as the concrete structures are concerned.
An attempt was made to study the structural element (namely column) which is
made of two differentmaterials. The column was made of Hollow Cold Formed Steel as
outer skin (stay-in-place form) and Self-Compacting Concrete (SCC) as filler.
Compared to concrete-filled composite columns, the Hollow columns can reduce
its own weight while having high flexural stiffness. SCC is an innovative concrete that is
able to flow under its own weight, completely filling formwork and achieving full
compaction, even in the presence of less hollowness ratio.
The experimental program was aimed to study the effect of thickness of sheet in
the performance of hollow composite columns using SCC as filler. An attempt was made
to study the properties of fresh and hardened concrete. Four trial mixes of SCC were
prepared and the mix with the characteristic strength of M25 was ascertained.
Later, Nine Hollow composite columns without spacers [three of each thickness
1.1, 1.6 and 2mm] were cast. Testing for each set of specimen are studied and compared
with SCC (RCC).
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
1. INTRODUCTION
Cold-formed steel tubular structures are being increasingly used for structural
applications. This is due to the aesthetic appearance, high corrosion resistance, ease of
maintenance and ease of construction. Hollow columns consisting of two concentric
circular thin steel tubes with filler between them have been investigated for different
applications.
In composite construction, the concrete and steel are combined in such a fashion
that the advantages of both the materials are utilized effectively in composite column.
The lighter weight and higher strength of steel permit the use of smaller and lighter
foundations. The subsequent concrete addition enables the building frame to easily limit
the sway and lateral deflections. Hollow column has less self weight and a high flexural
stiffness and hence its usage in seismic zone proves promising. It reduces requirements
on labor and construction time and maintains the construction quality.
1.1 Features of Hollow Column:
i. Column sections using Hollow Tube Filled with concrete can be reduced because
of its high strength.
ii. Vibrations caused by earthquakes and winds can be reduced due to its higher
rigidity than that of steel structure.
iii. Fire-resistant coating can be reduced or omitted due to the effect of concrete filled
in steel tubes.
Self-compacting concrete (SCC) is an innovative concrete that does not require
vibration for placing and compaction. The SCC proves much advantageous to be used in
hollow columns due to its self compacting ability. The placing of this concrete is easy
and rapid.
1.2 Need for Hollow composite column:
i. Increased strength for a given cross sectional dimension.
ii. Increased stiffness, leading to reduced slenderness and increased buckling
resistance.
iii. Significant economic advantages over either pure structural steel or reinforced
concrete alternatives.
iv. Identical cross sections with different load and moment resistances can be
produced by varying steel thickness, the concrete strength and reinforcement. This
allows the outer dimensions of a column to be held constant over a number of
floors in a building, thus simplifying the construction and architectural detailing.
v. Erection of high rise building in an extremely efficient manner.
vi. Formwork is not required for concrete filled tubular sections.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
1.3 Need for self-compacting concrete:
i. Faster construction and reduction in site manpower
ii. Excellent surface quality without blowholes or other surface defects
iii. Easier placing and improved durability
iv. Reduced noise levels, absence of vibration during casting
2. Hollow Composite Columns Using SCC
Steel members have the advantages of high tensile strength and ductility, while
concrete members may be advantageous in compressive strength and stiffness. Many
researchers agree that composite members utilize the advantages of both steel and
concrete. They are comprised of a steel hollow section of circular or rectangular shape
filled or centrifuged with plain or reinforced concrete. Figure 1. Shows the various types
of composite columns (a) Concrete encased steel (CES), (b) CFST, (c) combination of
CES and CFST, (d) Hollow CFST sections, (e) Hollow double skin sections.
Various types of composite columns
The main effect of concrete is that it delays the local buckling of the tube wall and
the concrete itself, in the restrained state, and is able to sustain higher stresses and strains
when unrestrained. These composite columns can be also used for the resisting outside
pressure, such as ocean waves, ice; in seismic regions because of excellent earthquake-
resistant properties such as high strength, high ductility, and large energy absorption
capacity. Concentrically layered hollow CFST elements are more effective than ordinary
hollow elements, because of the interaction between surfaces of concrete layers which
appears after spinning .This interaction appears independently on the type of loading
applied to such hollow CFTS element and on the increased load-bearing capacity of the
components.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
2.1 Method of Achieving Self Compatibility:
There are three key aspects of workability which require to be carefully controlled.To
ensure satisfactory performance during its wet phase and for successful classification as
SCC: Figure 2. shows the Method of Achieving Self Compactibility.
1. Filling ability – the ability of the concrete to flow, maintaining homogeneity
whilst undergoing the deformation necessary to completely fill the formwork,
encasing the reinforcement and achieving compaction through its own weight.
2. Resistance to segregation – the facility of the particle suspension to maintain a
cohesive state throughout the mixing, transportation and casting process.
3. Passing facility – the ability to pass through closely spaced rebar‘s or enters
narrow sections in formwork, and to flow around other obstacles without blocking
due to aggregate lock.
2.1.1. Materials
The materials that are used in the production of Self Compacting Concrete are
cement, fine and coarse aggregate, and a viscosity-modifying agent and High Range
Water Reducer. The properties of the ingredients are given below.
2.1.2 Cement
Through out this investigation, 53-Grade Ordinary Portland cement [Birla super]
will be used coarse aggregate. Locally available hard granite broken stone jelly of
maximum size 12.5mm-10mm will be used for investigations. The aggregates are clean
and free from deleterious materials.
2.1.3 Fine aggregate
Clean river sand, Grading of which in conformity to IS-383 will be used
2.1.4 Water
Clean, portable drinking water available in the college campus will be used.
2.1.5 Super plasticizer
High Performance Superplasticising Admixture used: CONPLAST SP430
Description:
a) Brown solution based on selected sulphonated naphthalene polymers.
b) Improved cohesion and particle dispersion
c) Major reduction in water/cement ratio
d) Chloride free, safe for use in prestressed and reinforced concrete.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Uses:
a) To all types of concrete with cem i or cem ii cement.
b) Is delivered ready for use.
c) It is recommended to be added to the concrete separately with the mixing water
Dosage:
0.7 –2.0 l / 100 kg cement
2.1.6 Viscosity modifying agent (VMA)
Viscosity Modifying Admixture used: GLENIUM STREAM 2
Uses:
a) Rheodynamic Self-Compacting Concrete
b) Concrete containing gap-graded aggregates
c) Lean concrete mixtures
d) Concrete containing manufactured sand
Advantages
a) Increased viscosity & thixotropic properties
b) Improved stability during transport & placing
c) Controlled bleeding
d) Reduced segregation, even with highly fluid mix
e) Enhanced pumping and finishing
f) Reduced sagging – dimensional stability
g) Enables flexibility in mixture proportioning
Mechanism of action:
Mixture of water soluble copolymers is absorbed onto the surface of the cement
granules, changing the viscosity of the water and influencing the rheological properties of
the mix.
Dosage:
50 to 500 ml/100 kg of cementitious material.
3. EXPERIMENTAL WORK
From the varies trial mix the mix proportion form M25 are arrived .It satisfies the
requirement of both the rheoplastic and the strength aspect and hence is used in the
casting of hollow composite column. Columns are cast for varies Diameter to thickness
ratio like using SCC, R.C.C with SCC .
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
3.1 Test methods for SCC:
The test methods to assess properties in fresh state are given
Lists of Test Methods for Self Compacting Concrete
Property Test methods Suggested values
Filling ability
Slump flow
T50cm slump flow
V funnel
650-800mm
2-7sec
8-12sec
Passing ability L box(H2/H1)
U box(R1-R2)
0.8-1.0
0-30mm
Segregation resistance V funnel at T5min +3sec
The experimental investigations were carried out in 2 phases. In phase I, ―Trial
mixes‖ were cast and final mix proportion was arrived. Appropriate w/c ratio by slump
flow test for Self Compacting Concrete was determined. The fresh properties and
hardened properties are determined for Self Compacting Concrete. The hollow columns
of known slenderness ratio and known hollowness ratio without spacers were cast using
SCC as the filler material.
3.2. Determination of material properties:
Sieve Analysis was carried out for fine aggregate, coarse aggregate and the
graded aggregates were used for casting purpose. The strength of the steel used was
250mpa.
3.3. Test results on fresh concrete:
The following test were used to estimate the fresh concrete properties of Self
Compacting Concrete namely, Slump flow test, L box test, U box test, V funnel test by
adjusting the super plasticizer and VMA content to arrive a mix satisfying rheoplastic
characteristic.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Dimensions of the hollow column specimen
Sl.no Details Outer Tube Inner Tube
1. Height(l) 500 500
2. Diameter 114mm 40mm
3. Thickness
a). 1.1.mm
b). 1.6mm
c).2.0mm
In each tk 2 tubes
a) 1.6mm
b). 1.6mm
c). 1.6mm
In each tk 2
tubes
4. Diameter / thickness
Ratio a). 103.60 b) 71.25 c).57.00
5. Thickness ratio 6
6. Grade of Concrete M25
Two columns are cast for each thickness of the outer sheet and the specimen is
cured for 28 days. After curing cleaning and painting of specimen are done and tested.
3.4 Test Methods & Equipments:
The hollow column to be tested is placed in between the top and bottom faces of
the UTM. The ends are hinged supported with the help of ball and socket arrangement
and the load is applied axially under manual control and the deflection for each load
increment is noted in the center, top and bottom plates with the help of deflectometer as
shown in fig.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Cast Specimen for different D/t ratio Tested Specimen
Ultimate load for Hollow column
Experimental Ultimate load for
Hollow and RC column
Sl.
No
Description
of specimen
Column
ID
Exp.ultimate
load of the
specimen
(KN)
Avg.ulti
mate
load
(KN)
1 HCC for
D/t=103.6
A1 408
409
A2 410
2 HCC for
D/t=73.25
B1 482
484
B2 485
3
HCC for
D/t=57
C1 510
511
C2 512
4
RCC for
D/t=73.25
A1 291
290
A2 289
Hollow
Column
of
Different
D/t Ratio
Average
experimental
ultimate
load(KN)
Difference
between
HCC and
RC
column
Increased
% of load
of HCC
compared
with RC
column
HCC
column
RC
column
D/t=103.6 409. 290 119 244
D/t=73.25 484 290
290
194 150
D/t=57 511 221 131
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
0
100
200
300
400
500
600
0 50 100 150 200 250 300 350
Lateral Deflection (mm)
Lo
ad
(K
N)
D/t =57 (t =2mm)
D/t =71.25 (t=1.6mm)
D/t =103.64 (1.1mm)
R.C.C. Column
511484
409
290 290 290
112 112 112
0
100
200
300
400
500
600
1 2 3
D/t=57 D/t=73.25 D/t=103.6
Lo
ad
in
KN
Composite Column
Rcc Column
PC column
Load Vs Deflection of HCC and RC columns for Experimental Ultimate load for
Hollow, RC&PC different D/t ratio columns.
4. CONCLUSIONS:
The following conclusions are arrived from the experimental investigations:
1. Addition of the super plasticizer should be made after 60% addition of mixing
water to fulfill its purpose.
2. Usage of the super plasticizer increases the early strength of concrete
3. W/P ratio should be less to sustain the strength and rheoplastic properties of the
concrete.
4. Usage of graded coarse aggregate helps in achieving the characteristics strength
of SCC to a great extent.
5. Generally, when the thickness of sheet was increased, the load carrying capacity
of the composite columns was increased.
6. Comparing the results of composite columns with the ordinary reinforced
columns, the load carrying capacity is 156% times higher. This is due to
confinement effect of the steel shell
7. The presence of steel confinement prevents the crushing of the concrete.
8. The compressive strength of the hollow columns is comparatively less than the
fully confined columns.
9. The ductile capacity of the hollow column is higher than the ductile capacity of
the RC columns.
CONCLUSIONS:
The following conclusions are arrived from the experimental investigations:
1. Addition of the super plasticizer should be made after 60% addition of mixing
water to fulfill its purpose.
2. Usage of the super plasticizer increases the early strength of concrete
3. W/P ratio should be less to sustain the strength and rheoplastic properties of the
concrete.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
4. Usage of graded coarse aggregate helps in achieving the characteristics strength
of SCC to a great extent.
5. Generally, when the thickness of sheet was increased, the load carrying capacity
of the composite columns was increased.
6. Comparing the results of composite columns with the ordinary reinforced
columns, the load carrying capacity is 156% times higher. This is due to
confinement effect of the steel shell
7. The presence of steel confinement prevents the crushing of the concrete.
8. The compressive strength of the hollow columns is comparatively less than the
fully confined columns.
9. The ductile capacity of the hollow column is higher than the ductile capacity of
the RC columns.
REFERENCES:
1. The European Guidelines for Self-Compacting Concrete Specification, Production and
Use, May 2005,
www.efca.info or www.efnarc.org
2. Prof.Lin, Prof.Chien-Hung, August 2008, ―Self Consolidating Concrete in Hollow
Composite Columns‖, ACI
journal .
3 .Prof.Min-Lang Lin, Prof.Keh-Chyuan Tsai ―Mechanical Behavior Of Double-Skinned
Composite Steel Tubular
Columns‖ National Center for Research on Earthquake
4 .Prof.Yan Xiao, Prof. Wenhui He ―Confinement Design Of Cft Column For Improved
Seismic Performance ―
5. Prof.Okamura,Prof.Ozama ,2003, ―Self Compacting Concrete‖,Journal Of Advanced
concrete Technology , Vol 1,
No1, Pg.5-15
6. Dr. R. Sri Ravindrarajah, D. Siladyi and B.Adamopoulos,August 2003‖Development
Of High-Strength Self-
Compacting Concrete With Reduced Segregation Potential‖ Proceedings of the 3rd
International RILEM Symposium,
1 Vol., 104
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
EXPERIMENTAL INVESTIGATION ON BEHAVIOUR OF
REINFORCED HIGH PERFORMANCE CONCRETE BEAMS
P.Muthupriya1, Dr.B.G.Vishnuram
2, Dr.K.Subramanian
3
1 Senior Lecturer, Department of Civil Engineering, VLB Janakiammal College of
Engineering and Technology, Coimbatore-641042.
2 Principal,Easa College of Engineering and Technology,Coimbatore-641 105.
3 Professor/Head, Department of Civil Engineering, Coimbatore Institute of
Technology, Coimbatore-641014.
Telephone:0422 2625626 Mobile:9677772322
[email protected], [email protected], [email protected]
ABSTRACT
The main objective of the present investigation is to study the behaviour of
reinforced high performance concrete beams under shear and flexure, using silica fume as
admixture. Apart from this a super plasticizer is used to achieve better workability. High
performance concrete (HPC) in this study was produced using mineral admixture silica
fume(SF) as partial replacement for cement considering three levels such as 0%, 5%,
7.5% and 10% respectively. Specimens (cubes, cylinders) were cast to study the strength
properties such as compressive strength (3, 7, and 28 days), split tensile strength (28
days). Water binder ratio was maintained at 0.32. Test results indicate that concrete
containing silica fume to an extent of 5% and 7.5% as partial replacement to cement
shows better strength characteristics when compared to the concrete with 10% of SF.
Henceforth, for the further investigation in testing of beams, 5% and 7.5% replacement
levels for silica fume were maintained to study the flexural and shear behaviour. Beams
of 100 x 200 x 2000 mm were cast for testing. Two- point loading was applied on the
beams. The Load versus deflection (P-∆) and moment versus curvature (M-φ)
characteristics were studied. The investigation suggests from the results obtained that the
reinforced high performance concrete beams using silica fume for 7.5% replacement
level have a better ultimate load carrying capacity than the control beams both in flexure
and shear.
Keywords: Reinforced High Performance Concrete, Silica fume, flexure and shear
behaviour.
INTRODUCTION
The usage of high strength concrete (HSC) in structural application has been
increasing worldwide. A few years ago, a characteristic compressive strength of
40N/mm2 would have been considered high. Nowadays concrete with characteristic cube
strength of 60N/mm2 and above is considered as a HSC.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
HPC using cement alone as a binder requires high paste volume which often leads
to excessive shrinkage and large evolution of heat of hydration, besides increased cost. A
partial replacement of cement by mineral admixtures such as silica fume, metakaolin,
fumed silica and ground granulated blast furnace slag (GGBS) in concrete mixes would
help to overcome these problems and lead to improvement in strength and durability of
concrete. This would also lead to additional benefits in terms of reduction in cost, energy
savings, promoting ecological balance and conservation of natural resources etc.
In India silica fume is a relatively new material. The interest in the silica fume
started with the strict enforcement of air pollution controls in many countries which
implies that the industry has to stop releasing silica fume along with other fine gases in to
the atmosphere. To find a solution to this problem studies were initiated and after some
investigations, it was found that silica fume could be used as a reactive pozzolanic
material in concrete.
A number of research works on silica fume have been reported with blended
cement and other pozzolanic materials like fly ash. The aim has been to develop early age
strength by using silica fume. Silica possesses little or no cementitious properties but in
finely divided form and in presence of moisture can chemically react with calcium
hydroxide generated in cement hydration process at ordinary temperatures to form
compounds possessing cementitious properties. While silica fume is used for achieving
higher strength and enhanced durability there are instances where it is used in
combination with fly ash. Silica fume is powerful pozzolanic material. The use of silica
fume in combination with a super plasticizer is a way to obtain HSC.
Silica fume In Concrete
The American Concrete Institute (ACI) defines silica fume as, ―very fine non-
crystalline silica produced in electric arc furnaces as a byproduct of the production of
elemental silicon or alloys containing silicon‖
Silica fume is usually referred to as
(a) Condensed silica fume
(b) Micro silica
(c) Volatized silica
Silica fume is used in concrete because it significantly improves the properties of
fresh concrete and hardened concrete.
OBJECTIVES OF THE INVESTIGATION
I. To study the material properties.
II. To determine the ultimate load carrying capacity of reinforced HPC beams.
III. To study the load-deflection characteristics.
IV. To study the moment-curvature characteristics.
V. To study the crack pattern in the beams.
The above studies on reinforced concrete beams containing silica fume are
compared with that of reinforced beams cast with normal concrete.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
MATERIALS AND METHODS
Ordinary Portland Cement (OPC) 43 grade conforming to IS 8112.
Locally available river sand as fine aggregate.
Crushed granite coarse aggregate of size 12.5mm as coarse aggregate.
Potable water for mixing of concrete and curing purposes.
Silica fume as mineral admixture.
A commercially available Sulphonated Naphthalene Formaldehyde based Super
Plasticizer as chemical admixture.
Tests on Cement properties
Tests were conducted to find the specific gravity, consistency, setting time,
soundness and compressive strength of OPC and the results are tabulated in Table 1. This
table also compares the results obtained and the requirement as per IS: 8112-1989.
Fine Aggregate
Tests were conducted to obtain specific gravity and fineness modulus of the fine
aggregate used in this study as per IS: 2386-1983 and the results are tabulated in Table 2.
Coarse Aggregate
Tests were conducted to obtain the specific gravity and fineness modulus of the
coarse aggregate used in this study as per IS: 2386-1983 and the results are tabulated in
Table 3.
Silica Fume
Silica fume is the commonly used mineral admixture in HPC. Silica fume is very
fine non crystalline silica, produced in electric arc furnaces, as a by product of the
production of elemental silicon or alloys containing silicon also known as condensed
silica fume or microsilica. It is mainly amorphous silica with high SiO2 content,
extremely small particle size and large surface area, highly reactive pozzolan used to
improve mortar and concrete.
Physical properties
The colour of silica fume varies from pale grey to dark grey. The specific gravity
of silica fume is 2.2. The specific surface area is 20,000m2
/kg. They are mostly fine
spheres with a particle size 0.1 to 1m. The chemical composition of silica fume is given
in Table 4, supplied by a Private Company Ltd, Mumbai.
Silica fume used in this study is shown in Fig. 1.
Super Plasticizer
Super plasticizer used in this investigation is sulphonated naphthalene polymer
based one and supplied as a brown liquid instantly dispersible in water.
EXPERIMENTAL INVESTIGATION
There is no specific method of mix design for HPC. The absolute volume method
was used to determine the quantities of different ingredients. In the mix proportions, air
content for concrete was assumed as 1%. The mixes M0, MS1, MS2 and MS3 were
obtained by replacing 0, 5, 7.5 and 10 percent of the mass of cement by silica fume. The
water binder ratio (w/b) of 0.32 for all mixes was maintained. In this study sulphonated
naphthalene type super plasticizer is used as chemical admixture. The mix proportioning
details for various mixes of the concrete are given in the Table 5 below.
All the test specimens such as cubes and cylinders shown in Figs. 2 and 3 were
cast using steel moulds. The specimens were removed from the mould after 24 hours and
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
cured in water. The cube specimens were tested for compressive strength, whereas
cylinder specimens were tested to study split tensile strength. The beam specimens were
tested to study the flexural as well as shear behaviour. The details of test specimens are
tabulated in the Table 6.
REINFORCEMENT DETAILS OF BEAMS
Flexure Beam Detailing
The reinforcement detailing for the beams tested for flexural
behaviour is shown in Fig.4.
Shear Beam Detailing
The reinforcement detailing for the beams tested for shear behaviour
is shown in Fig.5.
EXPERIMENTAL SETUP
All the beam specimens were cast at the structural laboratory. The raw materials
for concrete mixes already described in the previous section were mixed by a rotary
mixer. The wooden moulds were prepared and lubricated with oil before the concrete was
poured. The reinforcement bars were cut to the required lengths. The longitudinal bars
and stirrups were secured to each other at correct spacing by means of binding wires. A
mixing time of 3 to 5 minutes was given to ensure uniform mixing. The specimens were
demoulded after 24 hours and cured for 28 days using wet gunny bags. After curing
period, the beams were kept for 24 hours in a dry state. After drying they were cleaned
with a sand paper to remove all grit and dirt. Then all the specimens were prepared by
white washing from all sides. White washing was done to facilitate easy detection of
crack propagation.
A total of six beam specimens were cast. Out of six beams cast, two were
conventionally reinforced concrete beams. Remaining four beams were separated into
two categories and were cast with concrete, one with the 5% silica fume and the other
with 7.5% silica fume. All the beams were tested for flexure and shear under a loading
frame of capacity 1000kN. These beams were tested on an effective span of 1500mm
with simply supported conditions under two- point loading. Deflections were measured
under the loading points and at the mid span using Linear Variable Differential
Transducers (LVDTs). A typical two-point loading experimental set up is shown in the
Fig.6. The crack patterns were also recorded at every load increment. All the beams were
tested up to failure. The pivot arrangement for measuring strain is shown in the Fig.7.
RESULTS AND DISCUSSIONS
Compressive Strength Test
The compressive strength of concrete is determined at the age of 3, 7 and 28 days
respectively using cubes. The test was carried out on 150mm x 150mm x 150mm size
cube. A 2000kN capacity standard Compression Testing Machine (CTM) was used to
conduct the test. Three cubes are cast for each proportion.
The tested compressive strength for various mixes M0 to MS3 at the age of 3, 7,
and 28 days are given in Table 7. Test results indicate that when silica fume is added as
additional admixture, there is a significant improvement in the strength of concrete
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
because of high pozzolanic action to form more calcium silicate hydrate (CSH) gel. The
maximum cube compressive strength is obtained for Mix MS2 with 7.5% of silica fume
and its 28 days strength is 68 MPa. The increased strength is due to high reactive silica
present in silica fume concrete. The maximum compressive strength of concrete in
combination with silica fume is based on two parameters that are the replacement level
and the age of curing. The comparison of compressive strength for various mixes is
shown in Fig. 8
Split Tensile Strength
Cylinders (100x200mm) were cast to determine split tensile strength. Tests
were carried out according to IS 5816-1970 to obtain the split tensile strength for various
concrete mixes. The split tensile strength at the age of 28days for various mixes varies
from 4.395 to 5.563 MPa.
It was observed that for mix MS2 with 7.5% silica fume shows higher split
tensile strength. The strength is about 23.7% more than the control concrete mix.
The rate of increase of split tensile strength when compared to compressive
strength is less. The split tensile strength for various mixes at the age of 28 days are
tabulated in Table 8 and graphically represented in Fig. 9.
Split Tensile Strength = LD
P
2
Where,
P=Load in kN
L=Length in mm
D=Diameter in mm
Indian standard code (IS 5816) suggests a value of 0.7 ckf for split tensile strength. In
this test we obtained a split tensile strength of 5.563 MPa, for Mix MS2 replaced with
7.5% silica fume, which is more than the value suggested by the code.
Beam Test Results
The failure and the crack pattern of beam specimens tested for flexure are shown
in Fig.10 and Fig 11 respectively. The shear failure of beam is shown in Fig.12. The test
results for beam tested for flexure and shear are shown in Tables 9 and 10.
Load Vs Deflection Curves
The load versus deflection curves for flexure and shear beam specimenns are
shown in Fig.13 and Fig.14 respectively.
Discussion of Beam Test Results
Test results of beams under flexure indicate that, the beam with 7.5% of silica
fume (FMS2) has the highest load carrying capacity of 95kN. This is about 2.3 times
higher than that of the control beam (FCM). The first crack appeared at a load of 30kN
for FCM and FMS1 beams, whereas the first crack for FMS2 beam appeared at 35kN
load. This shows that 7.5% silica fume replaced beams show a better load carrying
capacity than the other two companion beams. At every load increment it was observed
that the FMS2 beam has the higher deflection values compared to that of the control
beam. The deflection values obtained are well below the serviceability condition
provided by the code provision.
In case of shear behaviour tests, the first crack appeared at the load of 24kN for
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
SCM beam where as the first crack load was 30kN for SMS2 beam which is 80% higher
than that of the control beam. The ultimate load of SMS2 beam is 92kN which is 33%
higher than that of the first crack load of control beam. Beams for whose values of shear
spans a/d<6 failed due to combined effect of bending and shear. A crack is first initiated
by flexure in the vertical direction, which further propagates in an inclined direction
towards the load due to the combined action of flexure and shear. With further increase in
load, the crack further progresses up to point in the compression zone and at some stage it
becomes unstable, splitting the beam into two segments I and II. This mode of failure is
termed as diagonal tension failure or shear flexure failure.
For all the beams tested in flexure, ultimate load carrying capacity obtained
experimentally is greater than the value obtained theoretically. The curvature is greater
experimentally compared to that of theoretical values. Due to this increase of curvature
the deflection is also increased. The deflection is within the allowable limit. The first
crack appeared at the jack load of 35kN and 30kN for flexure and shear beams
respectively. The ultimate load is higher in the 7.5% silica fume replaced beams in both
shear and flexure.
From the moment-curvature relationship, within the yielding stage the 5% silica
fume beams show higher stiffness than the control and 7.5% silica fume beams. But in
the plastic stage, the 7.5% beams (FMS2) show better ductility behaviour compared to
that of conventional and 5% silica fume replaced beams.
CONCLUSION
1. The compressive strength of high performance concrete containing 7.5% of silica
fume is 11% higher than that of the normal concrete.
2. Indian standard code (IS 5816) suggests a value of 0.7 ckf for split tensile
strength. In this test we obtained a split tensile strength of 5.563 MPa, which is
more than the value suggested by the code.
3. The ultimate load carrying capacity obtained experimentally is greater than the
value obtained theoretically for both shear and flexure beams. The curvature is
greater experimentally compared to that of theoretical values. Due to this increase
of curvature the deflection is also increased.
4. The addition of 7.5% of silica fume has considerably increased the load carrying
capacity as well as the deflection, both in flexure and shear beam specimens than
the control beams.
ACKNOWLEDGEMENT
The investigations, reported in this project report, were carried out at the Concrete
and Structures Laboratory. The authors would like to place on record their appreciation
and thanks to the Management and staff of Civil Engineering Department, VLB
Janakiammal College of Engineering and Technology, Coimbatore for their assistance
and co-operation throughout the investigations.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
REFERENCES
1. Adam Neville and Pierre Claude Aitcin(1998). ―High Performance Concrete – An
Overview‖, Materials and Structures, Vol.32, March 1998, pp.111-117.
2. Edward F‘ O Neil and Charles A. Weiss, Jr.(2001). ―Strength And Durability Of
Low Cost , High Performance Concrete‖, High Performance Materials and
Systems Research Program, Information Bulletin, June 2001, pp.01-13.
3. Ganesan N. and Sekar T. (2003). ―Mechanical Properties of Super Plasticized
Micro Silica High Strength Concrete‖ ICI Journal, October – December 2003,
pp.37-40.
4. Hassan K.E., Carbera J.G., Maliehe R.S.(2002) ―The Effect Of Mineral
Admixtures On The Properties Of High Performance Concrete‖, Cement and
Concrete Composites 22 (2002), pp.267-271.
5. IS 456-2000, ―Plain and reinforced concrete code of practice‖, BIS, New Delhi,
India.
6. Rachel J.Detwiler and P. Kumar Mehta(1989). ―Chemical And Physical Effects
Of Silica Fume On The Mechanical Behaviour Of Concrete‖, ACI Materials
Journal, Title No.86,M60, November-December 1989, pp.610-614.
7. Ravindra S.R. and Dr. Mattur C. Narasimhan(2003). ―Experimental Studies On
High Strength Micro Silica Concrete‖, ICI Journal, July – September 2003, pp.19
– 22.
8. Ravindra S.R. and Dr.Mattur C.Narasimhan (2003). ―Experimental Studies on
High Strength Micro Silica Concrete‖, The Indian Concrete Journal, July-Sep,
pp.19-22.
9. Said Iravani (1996). ―Mechanical Properties of High Performance Concrete‖, ACI
Materials Journal, Sep-Oct, Vol.93, No.5, pp.416-425.
10. Santanu Bhanja and Bratish Sengupta(2003). ―Optimum Silica Fume Content And
Its Mode Of Action On Concrete‖ , ACI materials journal, September – October
2003, pp. 407-412
11. Shetty M.S (1997).―Concrete Technology‖, S.Chand and Company Limited, New
Delhi.
12. ―SILICA FUME – USER‘S MANUAL‖ by Silica Fume Association, April,2005.
13. Tiwari A.K.(2005). ―Advances In High Performance Concrete – The Fifth
Ingredient‖, Civil Engineering and Construction Review, June
14. 2005,pp.28-38.
15. Venkatesh Babu D.L. and Krishnamoorthy R. (2005). ―Studies on Strength and
Durability Characteristics of High Performance Silica Fume Concrete‖, The
Master Builder, July-Aug, pp.73-75.
16. Venkatesh Babu D.L, S.C. Natesan (2003). ―Studies On Strength And
Durability Characteristics Of High Performance Silica Fume Concrete‖,
Proceedings of the INCONTEST 2003, September 2003, pp.262 – 267.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Table 1 Properties of 43 grade OPC
Table 2 Properties of Fine Aggregate
Test particulars Result obtained
Specific gravity 2.67
Fineness modulus 2.25
Size Passing through 4.75mm sieve
Table 3 Properties of Coarse Aggregate
Test particulars Result obtained
Specific gravity 2.80
Fineness modulus 5.96
Size Passing through 20mm sieve and
retained in 10mm sieve
Test particulars Result obtained
Requirements as per
IS:81121989
Specific gravity 3.15 3.103.15
Normal consistency
(%) 31 3035
Initial setting time
(minutes) 37 30 minimum
Final setting time
(minutes) 570 600 maximum
Compressive strength
(MPa)
a) 3 days 28 23
b) 7 days 38 33
c) 28 days 44 43
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Table 4 Chemical Composition of Silica Fume
Constituent Percentage
(%)
SiO2 9096
Al2O3 0.50.8
MgO 0.51.5
Fe2O3 0.20.8
CaO 0.10.5
Na2O 0.20.7
K2O 0.41
C 0.51.4
S 0.10.4
Loss of ignition
(C+S) 0.72.5
Table 5 Mix Proportioning Details
Mix Cement
(kg/m3)
S.F.
(kg/m3)
Fine
Aggregate
(kg/m3)
Coarse
Aggregate
(kg/m3)
SP
(Lit/m3)
w/b
M0 500 0 716.916 1100 4.16 0.32
MS1 476.190 23.8 716.916 1100 6.25 0.32
MS2 465.116 34.88 716.916 1100 7.30 0.32
MS3 454.54 45.45 716.916 1100 8.40 0.32
Table 6 Details of Test Specimens
Table 7 Compressive Strength Test Results
Sl.No Nature Of Test Size Of Specimens (m)
1 Compression
test 100x100x100.
2 Split tensile test 100 diameter, 200 height.
3 Beam
specimens 100x200x2000.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Table 8 Split Tensile Strength Test Results
Mix % of Silica Fume 28 Days(MPa)
M0 0 4.395
MS1 5 4.819
MS2 7.5 5.563
MS3 10 4.8
Table 9 Flexure beam test results
Table 10 Shear beam rest results
Fig .1Silica Fume
Fig.
2
Mix Silica Fume in
%
3Days (MPa) 7Days
(MPa)
28Days (MPa)
M0 0 43 50.5 60.5
MS1 5 42 52 64
MS2 7.5 43 53 68
MS3 10 40 50.5 60
Description
of test
specimens
% of Silica
Fume
First Crack
load (kN)
Ultimate
Load (kN)
Deflection
at Ultimate
Load (mm)
FCM Beam 0 30 72 15.65
FMS1 Beam 5 30 90 20.9
FMS2 Beam 7.5 35 95 23.6
Description
of test
specimens
% of Silica
Fume
First
Crack load
(kN)
Ultimate
Load (kN)
Deflection
at Ultimate
Load (mm)
SCM Beam 0 24 75 4.36
SMS1 Beam 5 27 87 5.61
SMS2 Beam 7.5 30 92 6.40
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Cube and Cylinder Specimen Fig .3 Specimens after curing
Fig. 4 Reinforcement detailing of Flexure Beam
Fig .5 Reinforcement Detailing of Shear Beam
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Co
mp
ress
ive
Stre
ngt
h
Fig .6 Experimental Test set up Fig.7 Arrangement of Pivots
Fig.8 comparison of Compressive Strength for various mixes
Fig.9 splitting tensile strength for various mixes
Fig. 10 Failure of Flexure Beam Fig.11 Crack Pattern of Flexure Beam
Mix
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Fig.12 Shear failure of Beam
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25
Deflection (mm)
Lo
ad
(kN
)
FCM
FMS1
FMS2
0
10
20
30
40
50
60
70
80
90
100
0 2 4 6 8
Deflection (mm)
Lo
ad
(kN
)
SCM
SMS1
SMS2
Fig.13 Load Vs Deflection curve for Fig.14 Load Vs Deflection curve
flexure beam for shear Beam
0
5
10
15
20
25
0 50 100 150 200 250 300 350
Curvature (rad/mm) x 10-6
Mo
men
t in
kN
m
FCM
FMS1
FMS2
Fig.15 Moment Curvature relationship for flexure beams
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
NEW TECHNIQUES IN ASEISMIC DESIGN
A.K.Kaliluthin1 S.Ramanathan
2
Lecturers, Department of Civil engineering, V.R.S.College of Engineering & Technology-Arasur
Villupuram, Tamil Nadu
INTRODUCTION:
Modern seismic design relies upon the inelastic response of structural members and
system to dissipate the energy imparted to a structure by an earthquake. Base isolation technique
has become an increasingly applied structural design technique for buildings and bridges in
highly seismic areas. The objective of a seismic isolation system is to decouple the building
structure from the damaging components of the earthquake inputs motion that is to prevent the
superstructure of the building from absorbing the earthquake energy. The entire superstructure
must be supported on discrete isolators whose dynamic characteristics are chosen to uncouple the
ground motion. Displacement and yielding are concentrated at the level of the isolation devices,
and the superstructure behaves very much like a rigid body. The main feature of the base
isolation technology is that it introduces flexibility in the structure. This helps in further reducing
the seismic response of the building.
BASE ISOLATION TECHNIQUE:
Concept of Base Isolation:
One of the most widely implemented and accepted seismic protection system is
base isolation. Seismic base isolation is a technique that mitigates the effects of an earthquake by
essentially isolating the structure and its contents from potentially dangerous ground motion
.especially in the frequency range where the building is most affected .the objective is to
simultaneously reduce linear-storey drifts and floor accelerations to limit or avoid damage not
only to the structure but also its contents , in a cost-effective manner.
Seismic base isolation is emerging as on alternative approach for earthquake protection of
structures. The basic concept of this approach is to uncouple a structure from the ground by
interposing a flexible element /bearing between the structure and foundation. Many buildings
have been constructed on some type of rubber bearings, and such structures have shown superior
performance in earthquakes.
The aim of the base isolation is to minimize the energy that is transferred from ground
motion to the structure by buffering it with a bearing layer at the foundation which has relatively
low stiffness. The bearing level longer period than the superstructure, which reduces the force
and displacements demands on the superstructure, allowing it to remain elastic and generally
undamaged. As a result of flexibilization, the natural period of the past fixed-base structures
undergo a jump and the new base isolation structure has a new natural period. The flexibility of
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
the interposing layers between structure and its foundation lead to a bigger fundamental period
for structural ensemble.
Need for Base Isolation:
Base isolation technique is necessary for the following situations:
Building is located in a high seismic intensity zone
Building should be operational in post-earthquake period such as hospital, school, water
tank,etc
Limitations exist with the lateral force restraining system or due to construction scheme
such as precast construction scheme or masonry construction scheme.
Existing structure is unsafe.
Minimize the damage to primary and secondary structural members.
Cost economics of the structure with and without isolators.
Elements of seismic base isolation system:
Seismic base isolator consists of energy dissipation core (lead plug), vulcanized rubber
layers, steel reinforcing plates, bottom mounting plate and cover rubber as shown in figure.
Energy dissipation core reduces earthquake forces and displacements by energy dissipation and
also it provides wind resistance. Rubber layer provides lateral flexibility to the system. Steel
reinforcing plates provide vertical load capacity and also it confines lead core. Bottom mounting
plate is integrated with the isolator and it is used to connect the structure below and above
isolator. Rubber is used to protect the steel plate.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Fig: 1 Isolator
Fig: 2 Rubber Bearing (RB) System
TYPES OF SEISMIC BASE ISOLATION SYSTEM
There are two basic types of isolation system. The system that has been adopted most
widely in recent years is typified by the use of elastomeric bearings, where the elastomer is made
of either natural rubber or neoprene. In this approach, the building or structure is decoupled from
the horizontal components of the earthquake ground motion by interposing a layer with low the
horizontal stiffness between the structure and the foundation. This layer gives the structure, a
fundamental frequency that is much lower than its fixed base frequency and also much lower
than the predominant frequencies of the ground motion. The first dynamic mode of the isolated
structure involves deformation only in the isolation system, the structure above being to all
intents and purposes rigid. The higher modes that produce deformation in the structure are
orthogonal to the first mode and consequently also to the ground motion. These higher modes do
not participate in the motion, so that if there is high energy in the ground motion at these higher
frequencies, this energy cannot be transmitted into the structure the isolation system does not
absorb the earthquake energy, but rather deflects its through the dynamics of the system. This
type of isolation works when the system is linear and even when undamped; however, some
damping is beneficial to suppress any possible resonance at the isolation frequency.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
The second basic type of isolation system is typified by the sliding system. This works by
limiting the transfer of shear across the isolation interface. The sliding system are simple in
concept and have a theoretical appeal. A layer with a defined coefficient of friction will limit the
accelerations to this value and the forces which can be transmitted will also be limited to the
coefficient of friction times the weight. Sliding movements provides the flexibility and force –
displacement trace provides a rectangular shape that is the optimum for equivalent viscous
damping.
RESPONSE OF BUILDINGS:
As a result of an earthquake, ground beneath each building begins to move, say first to
left, building responds with movement, which tends towards the right that is the building
undergoes displacement towards right (fig-3). The building‘s displacements in the direction
opposite to ground motion is actually due to inertia. The inertial forces acting on a building all
the most important of all those generated during an earthquake. But when the ground shakes,
isolated buildings do not move. No inertia forces transferred to the building due to shaking of the
ground. The inertia force acting on buildings have been reduced. Acceleration is decrease d
because base isolation system lengthens a building‘s period of vibration. And in general,
structures with longer period of vibration tend to reduce acceleration. While those this shorter
period tend to increase or amplify acceleration. The inertial forces which the building undergoes
are proportional to the building‘s acceleration during ground motion.
Fig: 3 Isolated Structure Conventional Structure
CRITERIA TO BE MET BY BUILDING FOR EFFECTIVE BASE ISOLATION:
Not founded on soft soil.
Buildings of low to medium height (H/L <1,f(0.1-0.3 Hz), and usually heavy).
Contents of building sensitive to high frequency vibration.
Lateral loading system making the building rigid.
Wind lateral load and other non-earthquake loads < 10% weight of structure.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
EFFECTIVE BASE ISOLATION:
The base isolation systems reduces the base shear primarily because the natural vibration
period of the isolation mode, providing most of the response, is much longer than the
fundamental period of the fixed base structure, leading to a much smaller spectral ordinate. The
higher modes are essentially not excited by the ground motion, although their pseudo-
acceleration are large because their modal static responses are very small.
The primary reason for effectiveness of base isolation in reducing earthquake induced
forces in a building is the lengthening of the mode period. The damping in the isolation system
and associated energy dissipation is only a secondary factor in reducing structural response.
APPLICATIONS AND ADVANTAGES OF BASE ISOLATION:
Base isolation systems are found useful for short period structures, say less than 0.7 s
including soil-structure interaction. Base isolation provides an alternative to the conventional,
fixed –base design of structures and may be cost effective for some new buildings in locations
where very strong ground shaking is likely. It is an alternatively for buildings that must remain
functional after a major earthquake. (e.g. hospital, emergency communication centre , computer
processing centre‘s etc.) Several new buildings have been isolated using rubber or elastomeric
bearings. Several commercial brands of base isolators are now available in the market especially
in foreign countries. Care should be taken to identify the most suitable type of device for a
particular building.
Fig: 4 Isolator Components between the Foundation and Superstructure
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Fig: 5 Base Isolation in Buildings
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
BASE ISOLATION IN INDIA
The first base isolation structure is the new 30,000 m2 with 300 beds, Bhuj hospital,
Gujarat reconstructed after the devastating earthquake of 26 Jan 2001 (fig- 6). It is reputed to be
able to stand a force of tremor on the Richter scale 10. It is being founded on Robison seismic
lead rubber bearings which will give it the highest possible earthquake protection. This will
protect the patients and ensure that the hospital will remain operational following future seismic
attacks.
Fig: 6 View of Basement in Bhuj Hospital building – built with base isolators after the
original District Hospital building at Bhuj collapsed during the 2001 Bhuj earthquake.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
SEISMIC DAMPERS:
Another approach for controlling seismic damage in buildings and improving their
seismic performance is by installing seismic dampers in place of structural elements, such as
diagonal braces. These dampers act like the hydraulic shock absorbers in cars – much of the
sudden jerks are absorbed in the hydraulic fluids and only little is transmitted above to the
chassis of the car. When seismic energy is transmitted through them, dampers absorb part of it,
and thus damp the motion of the building.
Dampers were used since 1960s to protect tall buildings against wind effects. However, it
was only since 1990s, that they were used to protect buildings against earthquake effects.
Commonly used types of seismic dampers include viscous dampers (energy is absorbed by
silicone-based fluid passing between piston-cylinder arrangement), friction dampers (energy is
absorbed by surfaces with friction between them rubbing against each other), and yielding
dampers (energy is absorbed by metallic components that yield) (Figure 7). In India, friction
dampers have been provided in a 18-storey RC frame structure in Gurgaon.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Fig 7: Seismic Energy Dissipation Devices – each device is suitable for a certain building.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
REFERENCES:
1. S.K.Thilakar,Base Isolation,Supplemental Damping And Active Control For Seismic
Construction.
2. S. Unnikrishna pillai and Devadoss Menon, Reinforced Concrete Design,2008
3.Duggal, Earthquale Resistant Design,2006
4. Pankaj Agarwal, Earthquake Resistant Design,2006
5. C.V.R.Murty,Indian Institute of Technology Kanpur,Kanpur, India, IITK-BMTPC
Earthquake Tips, Building Materials and Technology Promotion Council, New Delhi,
India.2002.
6.S.R.Damodarasamy,Basics of Structural Dynamics and a Aseismic
Design,Government College of Engineering ,Salem.2009.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
EXPERIMENTAL STUDY OF RETROFITTING WITH GFRP ON RC
ELEMENT UNDER FLEXURE
Mrs.N.R.Chitra *, R.Anitha Deel**, Dr.R.Murugesan
* Selection Grade Lecturer, Dept of Civil Engg, IRTT,Erode
** PG student, Dept of Civil Engg, IRTT,Erode, *** Asst.Prof., Dept of Civil Engg, IRTT,Erode
ABSTRACT
The study of the project is concerned with the investigation of properties of concrete by
wrapping with glass fibre reinforced polymer sheet (GFRP). The use of GFRP is emerging in
several applications in the construction industry, properties that are so different from those of
steel. These applications are found evenly in structural concrete, architectural concrete, and
masonry and both in new construction and repair and retrofits. These techniques can be adopted
for rehabilitation of earthquake affected structures.
Many researches have shown that the introduction of glass fibre into concrete and their
uniform disbursement give rise to higher strength like tensile strength, flexural strength, impact
strength, resistance to cyclic loading etc. can be improved by the wrapping of concrete.
Cubes, prisms and beams was also cast for M20 grade of concrete. These specimens will
strengthened with ISO branded GFRP wrap.
The properties of concrete with GFRP sheet wrapping was compared with those of the
conventional concrete (concrete without GFRP wrapping) from the experimental investigation, it
has been concluded that there is considerable improvements in compressive strength, tensile
strength and modulus of rupture of concrete with GRRP wrapping.
INTRODUCTION
Reinforced concrete beams are damaged due to over loading, errors in design and bad
construction. Effective strengthening technique is needed for the beams to regain their structural
capacity. Glass fibre reinforced polymer (GFRP) composites are increasingly used for this
purpose.
This experimental programme is used for studying this technique on simply supported
beams of rectangular cross section. Two sets of beams were tested – Normal beam with out
GFRP material, damaged and then wrapped with GFRP material.
Each beam was initially loaded above its cracking loads. The cracked beams were
wrapped in three ways (full wrapping, bottom wrapping, center wrapping).
Traditionally, repair of RC beams has been achieved by using bonding steel plates. But it
has several disadvantages like corrosion and increased self weight for long span. In recent years,
use of FRP as strengthening materials has shown great promise as an alternative material to steel
plates. Externally bonded FRP has emerged as a new structural strengthening technology for
strengthening of RC structures. These materials are superior to steel when it comes to comparing
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
the resistance to electro chemical corrosion, higher strength-to- weight ratio, durability, low
labour cost, and ease of handling and easy availability in required length or shape.
NEED FOR RETROFITTING
In present days the structures are in the aggressive environment. The old structures were
constructed in non aggressive environment without any special preventive measures are now
badly affected due to gradual deterioration of the environment around them. Not only that
whenever the building gets damaged and the rehabilitation work of the damage is economical
then that of the new construction, then obviously we opt for rehabilitation work. Monuments are
our national properties and we are supposed to safe guards those monuments, we cannot
demolish the deteriorated monuments. So we go for Retrofitting.
TYPES OF FIBRE
Although every type of fibre has been tried out in cement and concrete, not all of them
can be effectively and economically used. Each type fibre has its characteristics properties and
limitation. Some of fibres that could be used are steel fibres, glass, carbon, asbestos, coir,
polypropylene, nylons.
Fibre is a small piece of reinforcing material possessing certain characteristic properties.
They can circular or flat. The fibre is often described by a convenient parameter called ―aspect
ratio‖. The aspect ratio of fibre is the ratio of its length to its diameter. Typical aspect ratio
ranges from 30 to50.
Steel fibre is the one of the most commonly used fibre. Generally, round fibres are used.
The diameter may be varying from 0.25 to 0.75mm. The steel fibre is likely to get rusted and
lose some surface. Uses of steel fibres make significant improvement in flexural, impact and
fatigue strength of concrete.
Polypropylene and nylon fibres are found to be suitable to increase the impact
strength. They possess very high strength but their low modulus of elasticity and higher
elongation do not contribute to the flexural strength.
Asbestos is a mineral fibre and as proved to be most success full of all fibre, it can be
mixed with Portland cement. Tensile strength of cement varies between 5600 to 9800 kg/cm2.
Glass fibre is a recent introduction in fibre concrete. It has a very high tensile strength
(10200 to 14800 kg/cm2. Glass fibre, which is originally used in conjunction with cement, was
found to be affected by alkaline condition of cement
Carbon fibre perhaps posses very high tensile strength (21100 to 28150 kg/cm2) and
young‘s modulus. It has been reported that cement composite made with carbon fibre as
reinforced will have very high modulus of velocity and structural strength. The limited studies
have shown good durability. The use of carbon fibres for structures like cladding, panels cells
will have promising future
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Plastic fibres are a new invention in the field of fibre reinforced concrete. Reliance found out a
new type of fibres which are called REECRON3s fibres, which can be effectively used in
concrete and shotcrete works.
GLASS FIBRE REINFORCED POLYMER (GFRP)
The use of composite materials in civil engineering field is growing popular because of their
greater strength and efficiency.FRP is one of the composite materials obtained by reinforcement
of fibres in the polyester resin. The various types of fibres used may be glass fibres, carbon
fibres, asbestos fibres, whisker etc. FRP offer a combination of properties not easily found in
traditional materials. Most outstanding of them being high strength and dimensional stability at
low product weights.
Glass fibres are widely used type of reinforcement to produce glass fibre reinforced plastics
(GFRP).
Thus fibre reinforced plastics (FRP) are complete materials obtained by reinforcement of
fibres in the resin. In this fibre provides stiffness and strength while the resin provides a matrix to
transfer the load to the fibres, gives them stability and chemical resistant surface. The fibre
matrix interface is the critical factor that determines to what extent the potential properties of the
composite will be achieved and maintained during usage. The interface must have appropriate
chemical and physical features in order to provide the necessary load transfer from the matrix to
the reinforcement. The interfacial bond must resist stresses due to factors such as thermal
expansion of fibre and matrix and shrinkage of the resin during curing.
It is in the advent of fifties that the glass fibre reinforced plastics (GFRP) have made their
appearance into structural engineering. GRFP are essentially structural materials that compose
the versatile chemical, electrical and other properties of plastics with the mechanical strength,
chemical inertness and electrical resistance of glass fibres to create synergistic material which
can be engineered for specific applications.
EXPERIMENTAL WORK DETAILS
The beams are of 100 mm x 150 mm size and 1.1 m long simply supported and tested for
two point load for beams designed for shear failure.
The mix ratio and water cement ratio of concrete were kept constant. A mix ratio of 1:
1.425: 3.1 of cement, fine aggregates, coarse aggregates with water cement ratio of 0.5
was used for all beams.
All beams were provided with the main reinforcement of 2 numbers of 10 mm diameter bars are
provided at bottom and 2 numbers of 6 mm diameter bars are provided at top with shear
reinforcement of two legged stirrups of 6 mm diameter @ 90 mm c/c.
OBJECTIVES OF PRESENT INVESTIGATION
To study major application of GFRP sheets for seismic strengthening of RC columns
To know Shear strength and ductility of RC columns
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
To study about Shear strength should be strong enough to avoid brittle shear failure
To study about Type of glass fibre mat
To know Type of resin Araldite
To study Volume of fibre to resin that is 45% by weight
To study about the Thickness of GFRP sheet(fine filaments of diameter ranges 10-12
microns)
The main objective of experimental study is to examine the effectiveness of strengthening
material and externally bonded GFRP laminates to strengthen damaged flexural members.
LITERATURE REVIEW
Amlan K. Sengupta Asst professor in IIT Chennai.
The chapter starts with an explanation of the need of retrofit of buildings in India
with reference to the revisions of IS 1893. The measures emphasized by the national institute of
disaster management are highlighted the chapter explains the attributes of seismic design, goals,
objectives and steps of seismic retrofits. The performance based objectives are mentioned.
Options for considering reduced base shear for retrofits of older buildings are provided. There is
a glossary of terms associated with seismic retrofit.Repair & Rehabilitation of Structures
REINFORCEMENT DETAILS
All dimensions are in mm
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
REINFORCEMENT DETAILS OF NORMAL BEAM
All dimensions are in mm
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
REINFORCEMENT DETAILS OF FLEXURE BEAM
EXPERIMENTAL BEHAVIOUR OF BEAMS
The experimental work consisted testing of simply supported beams. All beams
had the same dimensions and flexural and shear reinforcements. The beam had 100 x 150 mm
rectangular cross section and a clear span of 1100mm. Two 8 mm diameter steel bar were used
for flexural reinforcement at the bottom & tow 6 mm diameter steel bar were for flexural
reinforcement at the bottom.6 mm stirrups were spaced every 90 mm for the shear reinforcement.
The concrete mix was proportioned to target strength of 20 N/mm2. Each cast used a hand mixed
concrete with coarse aggregate passing through 20 mm sieve and retained in 10 mm sieve,
locally available river sand as fine aggregate and 53 grade cement. The specimens were
compacted by a pate vibrator for good compaction. To monitor the strength of concrete, cube
specimen were cast for each batch of concrete and strength was obtained by testing cubes at the
age of 28 days curing.
TESTING PROCEDURE
All the beams were marked by 5 cm x 5 cm grids on both faces to mark the crack
pattern. The loading point, end points of the beam, centre line between centre of the beam and
end point of beam was marked.
Support and loading points were checked for any surface defects and small pits if any
were filled with plaster paste to make it even for proper distribution of load.
The beam specimens were divided into two groups:
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Group I: Normal Beam (NR), Flexural Retrofitting Beam 1(FR 1), Flexural Retrofitting Beam
2(FR 2), Flexural Retrofitting Beam 3(FR 3), without wrapping of GFRP material.
Group II: Normal Beam (NR), Flexural Retrofitting Beam 1(FR 1), Flexural Retrofitting Beam
2(FR 2), Flexural Retrofitting Beam 3(FR 3), with wrapping of GFRP material.
NR Beam is fully wrapped by using GFRP sheet. FR1 Beam is fully wrapped by using
GFRP sheet.FR2 beam is wrapped at the bottom by using GFRP sheet. FR3 beam is wrapped by
using GFRP sheet. Beam of these types were externally bonded with GFRP strips using epoxy
resin as per the procedure laid down by the manufacturer.
PREPARATION OF BEAM FOR FIXING GFRP
The beams and reference specimens were taken out after 28 days of curing and dirt on the
surface were wiped off and allowed to dry inside the room for two days. On the third day the
surface was hogged using hand hammer and cleaned thoroughly. Strengthening of beam was
provided by glass fiber reinforced polymer (GFRP) fabric.
GFRP Wrapping: PREPARATION OF RESIN
1. GFRP sheet for surface mat
2. Iso resin- Twice the times of the weight of surface mat (1 litre)
3. Catalyst (10 ml)
4. Accelerator & Solvent (10 ml)
FIXING OF VERTICAL STRIPS OF GFRP
1. Hogging the concrete surface to a width of 40mm at an interval of 20 mm up to 500 mm
length from the end of beam and cleaned thoroughly.
2. Coating chalk powder and mixed with ISO resin by 50% weight to avoid air gap.
3. Glass woven fabric cut to needed width an length and spreader on the resin coated
surface
4. Resin was poured on fabric mat by brush and gently pressed around the beam to get even
surface.
Left curing for 24 hours.
FIXING GFRP ON BEAMS
WRAPPING OF GFRP
1. Hogging the concrete surface using hand thoroughly all around the beam and column.
2. Coating with ISO resin at 50% by weight to avoid air gap.
3. Glass woven fabric cut to needle length and spreader on the surface of the beam.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
4. Resin was poured on fabric mat by gently pressing with brush.
5. Curing period for 24 hours for all the beam specimens treated with GFRP.On the next
day the grid lines of 2 cm x 2 cm were drawn on both sides of the beams to sketch crack
pattern. The location of support loading point, deflection point and center of beam were
marked.
WRAPPING OF GFRP MAT
TEST PROCEDURE AND INSTRUMENTATION
All the beam specimens were loaded simply supported and instrumented shown in
fig. the beam were then tested under two point loading. The load was applied through UTM.
Equal increment of 5 KN load were applied. During loading, mid-span deflection were readings
measured using dial gauge (0.01 mm). Load and deflection readings were recorded for each
stage. The results of all beams tests have been summarized in table 8-15. Crack formed on the
surfaces were marked and identified. The load and deflection characteristic were studied.
GROUP III
COMPARISON GRAPH ON FR1, F
R2, FR3 & FR4 are shown in fig no. 5.1 & 5.2
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
COMPARISON GRAPH FR1,FR2,FR3 & FR4 WITHOUT WRAPPING
COMPARISON GRAPH FR1,FR2,FR3 & FR4 WITH WRAPPING
CONCLUSION
Two groups of beam have been tested in this experimental study – Beams
without GFRP Laminate and repaired by GFRP laminate. Based on the test results, conclusions
can be drawn as follows:
The mid-span deflection at failure increases significantly due to strengthening of the
beam.
Beam strengthened with Glass Fibre Reinforced Polymer (GFRP) wrapping exhibited
relatively good ductile behaviour. Hence it contributes strengthening more effectively.
The number of cracks and crack width reduces as the beam was strengthened at lower
load levels.
Performance of repaired RC beams is significantly increased by using Glass Fibre
Reinforced Polymer (GFRP) wrapping. Therefore, this technique is effective to at least
restore the original strength of cracked beam.
The retrofitting of building and other structures for seismic forces has special challenges
as compared to the design and construction of new buildings.
The huge building stock poses challenge to the practicing professionals. They need easy-
to-understand principles, tools to analyze a building, retrofit, strategies that are practical
and maintain the functional requirement of a building, and estimate of the cost of retrofit.
When compared with the flexure beam without wrapping, GFRP strengthened beams
carries 17.8% more load for fully wrapped condition.
When compared with the flexure beam without wrapping, GFRP strengthened beams
carries 8.1% more load for bottom portion wrapped condition.
When compared with the flexure beam without wrapping, GFRP strengthened beams
carries 26.15% more load for middle third portion wrapped condition.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
When compared with the flexure beam without wrapping, GFRP strengthened beams
carries 38.64% more load for double layer wrapped condition.
6.2 SUGGESTIONS FOR FUTURE WORK
Following are the suggestions for future work:
1. We can try for three layer wrapping for improving its strength.
2. We can use some other type of resin also
3. This method can also adopted for some natural calamities
4. We can also follow some other type of failure like shear failure
REFERENCES
1. Amlan K. Sengupta Asst professor in IIT Chennai. A Hand Book of Seismic Retrofit of
Building.
2. Andrei M. Reinhorn1, Stefania Viti2 and GianPaolo Cimellaro, Retrofit of Structures.
3. Andreas J.Kappos and Alireza Manafpour, the seismic design of RC buildings with the
aid of advanced analytical techniques.
4. A.S. Elnashai and R. Pinho, test on repair and retrofitting of RC walls using selective
techniques.
5. Giuseppe Oliveto and Massimo Marletta, the seismic retrofitting of reinforced concrete
buildings using traditional and innovative techniques.
6. Saadatmanesh et al, an experimental investigation on strengthening of undamaged beams
with FRP laminates.
7. Dr.V.M.Sharma,Chief consultant, AIMIL Ltd., New Delhi. Repair & Rehabilitation of
Structures.
8. Uji (1992),the shear capacity improvement of a RC member by applying a CFRP sheet
on the web of a beam and suggested calculation model of shear debonding strength of
this type of strengthening.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
STRENGTHENING ON RC ELEMENTS WITH GFRP UNDER FLEXURE
P.Saravanakumar*, T.Srividya**,Dr.R.Murugesan***
*Lecturer, Dept of Civil Engg, IRTT,Erode
** Design Engineer, Chennai,*** Asst.Professor, Dept of Civil Engg, IRTT,Erode
ABSTRACT
The study of this project is concerned with the investigation of the efficiency of GFRP
composites in strengthening simply supported reinforced concrete beams designed with
insufficient flexure capacity. The use of GFRP is emerging in several applications in the
construction industry, properties that are so different from those of steel.Using hand lay-up
technique, successive layer of Glass fiber reinforced polymer are bonded along the flexure span
to increase the flexural capacity and to avoid catastrophic premature failure modesThe test
results of seven beams, addressing the influence of flexure strengthening and their flexure
capacity were compared with ultimate flexure capacity of R.C section using IS 456-2000.
INTRODUCTION
The urgent need to strengthen concrete structures is on the rise. Various motivations lead
to increase the demand for strengthening. Deterioration and ageing of concrete structures are not
the only reasons for strengthening beams. Other reasons include upgrading design standards,
committing errors in design or construction, exposure to unpredicted loads due to change in the
usage of the structure. Strengthening of concrete members is usually accomplished by
construction of external reinforcement on concrete or shot crete jackets, by epoxy bonding steel
plates to the tension face of the members or by external post tensioning.
One of the fast replacements for steel reinforcement is FRP. This Fiber Reinforced Plastic
show greater advantage over the conventional materials such as steel and other materials, Glass
Fiber reinforced Polymer (GFRP) composite posses high strength to weight ratio, tensile strength
compared to tor steel. The other enhancing properties of GFRP are, it is non reactive for
chemicals such as chlorides, alkalis and thermally non-conductive in nature and hence durability
of structures is increased. This calls for the use of GFRP as reinforcement for concrete structures
in which corrosion is the primary concern.
ADVANTAGES OF GFRP
1. Low Weight (Making them Much Easier to Handle On Site) – Reduction in Dead Load.
2. Immunity to Corrosion
3. Excellent Mechanical Strength and Stiffness
4. Attractive in Appearance and Architectural Beauty of the Structures
5. A Substantial Reduction of Overall Costs
6. A Major Improvement in the Safety of the Structure with respect to Seismic Risk
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
OBJECTIVE OF THE INVESTIGATION
In this investigation, it is aimed to study the Contribution of Externally applied GFRP to RC
beams in Flexure zone.
1. It is also aimed to compare the Experimental Ultimate Load and Deflection of GFRP
Wrapped Strengthened Flexure beams, with those of the Reference beams.
2. It is also aimed to compare the Experimental Ultimate Load and Deflection of Weld
Mesh Strengthened Flexure beam, with those of the Reference beams.
REVIEW OF LITERATURE
Saadatmanesh and Ehsani investigated the behaviour of concrete beams strengthened beams
using CFRP unidirectional sheets and CFRP woven fabrics. In all of these investigations, the
strengthened beams showed higher ultimate loads compared to non-strengthened ones. One of
the drawbacks experienced by most of these strengthened beams was considerable loss in beam
ductility. An examination of the load deflection, behaviour of the beams, however, showed that
the majority of the gained increase in load was experienced after the yield of the steel
reinforcement. In other words, a significant increase in ultimate load was experienced with out
much increase in yield load. Hence, a significance increase in service loads should hardly be
gained.Alfarabi Sharif, G. J. Al-Sulaimani, I. A. Basunbul, M. H. Baluch, and B. N. Ghaleb
experimentally investigated the Strengthening of Initially Loaded Reinforced Concrete Beams
Using FRP Plates. The behavior of the repaired beams is represented by load-deflection curves
and the different modes of failure are discussed. The results indicate that the flexural strength of
the repaired beams is increased.
EXPERIMENTAL STUDY
Glass fiber of E-class was used as fiber reinforcement. Woven fabric of fiber of E-class
of 600gm/sqm of uniform bi-direction fabric was used as fiber reinforcement and twice by
weight of fiber is used for bonding with RC beams. Iso thalmic resin was used for fixing of
GFRP sheets over beams. Accelerators and catalyst are the hardeners. Curing temperature govern
the catalyst of the hardener.Square weld mesh of 1 mm diameter with 15 mm spacing was used
for the strengthening of RC beam.
SELECTION OF THE MIX PROPORTION
Mix design was done as per IS Method for M20 concrete and attached in Appendix. The
mix ratio adopted for all the specimens were 1:1.425:3.1 by weight of cement, fine aggregate
and coarse aggregate and water cement ratio of 0.50.The actual material required for each
specimen was weighed and mechanically mixed and table vibrated for compaction
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
FIGURE 1 GLASS FIBER MAT
FIGURE 2 WELD MESH
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
REINFORCEMENT DETAILS
Main reinforcements for the normal reference beam (2 nos) with 2 numbers of 10 mm
diameter bars provided are at bottom and 2 numbers of 6 mm diameter bars are provided at top.
The details are shown in figure 3.4& 3.6.
Main reinforcements for the flexure beam with 2 numbers of 8 mm diameter bars
provided are at bottom and 2 numbers of 6 mm diameter bars are provided at top.
All the Dimensions are in mm
FIGURE 3 REINFORCEMENT DETAILS OF NORMAL BEAM
All the Dimensions are in mm
FIGURE.4 REINFORCEMENT DETAILS OF FLEXURE BEAM
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
FIXING GFRP ON BEAM ELEMENTS
WRAPPING OF GFRP
1. Clean the concrete surface thoroughly all around the beam.Coating with Iso thalmic resin
at twice the weight to avoid air gap.
2. Cut the Glass woven fabric according to size of the RC beam and spread on the surface of
the beam. Resin was poured on fabric mat by gently pressing with brush. After 24 hours
Curing period, all the beam specimens with GFRP is ready for testing.
FIGURE 5 WRAPPING OF GFRP MATFIXING GFRP ON BEAM ELEMENTS
BEHAVIOUR OF BEAMS
GENERAL
After preparation, the beams were tested under the universal testing machine of capacity
1000 kN. Load was applied gradually, during testing; formation and growth of cracks were
recorded on the beam by drawing line along the crack and marking the corresponding loads.
While taking readings, extreme care was taken not to touch any of the testing and measuring
equipments.
LOAD DEFLECTION BEHAVIOUR
The deflection corresponding to every 5kN increment was noted; The load at first crack is
also noted. Finally ultimate load at which the beam specimen was failed also measured.
COMPARISONS OF LOAD DEFLECTION BEHAVIOUR OF ALL BEAMS
The Load Deflection Behaviour of All Beams are Compared as Shown In Fig 6-8
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
FIGURE 6 Comparisons of load vs deflection Behaviour of
Normal& Normal Strengthened beams
\
FIGURE 7 Comparisons of Load vs Deflection Behaviour of Flexure &
Strengthened Flexure beams
0
10
20
30
40
50
60
70
0 10 20 30
Deflection(mm)
Lo
ad
(kN
)
Flexure
Flexure Strengthened
Beam(FS1)
Flexure Strengthened
Beam(FS2)
Flexure Strengthened
Beam(FS3)
0
10
20
30
40
50
60
70
80
90
0 5 10 15 20 25
Deflection(mm)
Lo
ad
(kN
) Normal Beam
Normal Strengthened
Beam
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
FIGURE 7 Comparisons of Load vs Deflection Behaviour of Flexure &
Weld Mesh Strengthened Flexure beams
LOAD CARRYING CAPACITY:
The beams were loaded up to the ultimate load for Normal beam was observed as 71 kN.
The ultimate loads for normal strengthened beam was observed as 81.5 KN .The ultimate loads
for normal flexure beam was observed as 60.4kN.Similarly, the ultimate loads for strengthened
flexure beams(FS1, FS2 & FS3) and weld mesh strengthened were 65kN, 63.5kN,65 kN & 65kN
respectively.
0
10
20
30
40
50
60
70
0 10 20 30
DEFELCTION (mm)
LO
AD
(kN
)
Flexure
Flexure Strengthened
Beam(FS1)
Flexure Strengthened
Beam(FS2)
Flexure Strengthened
Beam(FS3)
Weld Mesh
Strengthened
Beam(FSWM)
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
FIGURE 9 COMPARISONS OF LOAD BEARING CAPACITY OF ALL THE BEAMS
CONCLUSIONS
Based on the experimental investigation and discussions of results, the following
conclusions are made.
1. When compared with the Normal beam, GFRP Strengthened Normal beams
carries 14.8% more load.
2. When compared with the Reference Flexure beam, Normal Beam carries 17.54%
more load.
3. The GFRP Strengthened Flexure beam (on all four sides) result shows 7.6%
increase in the ultimate load compared to the Reference Flexure beam.
4. The GFRP Strengthened Flexure beam (on bottom half portion) result shows
5.13% increase in the ultimate load compared to the Reference Flexure beam.
5. The GFRP Strengthened Flexure beam (on mid one third portions) result shows
7.6% increase in the ultimate load compared to the Reference Flexure beam.
6. The Weld Mesh Strengthened Flexure beam result shows 7.6% increase in the
ultimate load compared to the Reference beam. This beam showed considerable
reduction in the size of the crack.
7. The Mid-Span increases significantly due to the strengthening of the beams.
In general,GFRP wrapping is an ideal material for improving the performance of
reinforced concrete beams.
REFERENCES
1. Alfarabi Sharif, G.J.Al-Sulsalamani, I.A.Basinbul, M.H.Baluch and
B.N.Ghaleb(1994)., ―Strengthening of Initially loaded Reinforced concrete beams
using plates‖, ACI Structural Journal ,p.p160-167.
2. C. Allen Ross, David M. Jerome, Joseph W. Tedesco, and Mary L. Hughes
(1999),―Strengthening of Reinforced Concrete Beams with Externally Bonded
Composite Laminates‖- structural journal,vol-2,p.p.212-220.
3. AnthonyJ. Lamanna, Lawrence C. Bank, and David W. Scott(2001), ―Flexural
Strengthening of Reinforced Concrete Beams Using Fasteners and Fiber-Reinforced
Polymer Strips‖,Vol-98,p.p.368-376.
4. O. Chaallal, M. -J Nollet, and D. Perraton(1998) , ―Strengthening of reinforced
concrete beams with externally bonded fiber-reinforced-plastic plates: design
guidelines for shear and flexure‖ Can. J. Civ. Eng. 25(4),p.p 692–704.
5. J. Compos ( 2003) ,―Experimental Investigation of FRP-Strengthened RC Beam-
Column Joints‖ Constr. Volume 7, Issue 1, pp. 39-49.
6. Grace N.F., Sayed G.A.Soliman.A.K.and Salehk.R( sep/oct-1999) ―Strengthening
of Reinforced concrete beams using fiber reinforced polymer (FRP) laminates‖, ACI
Structural Journal,p.p.865-874.
7. Marco Arduini and Antoinio Nanni, (1997 ) ,―Parametric Study of Beams with
Externally Bonded FRP Reinforcement‖, Structural Journal,vol-94,p.p.493-501.
8. Nabil F Grace, George Abdel-Sayed and Wael F.Ragheb(2002), ―Strengthening Of
Concrete Beams Using Innovative Ductile Fiber-Reinforced Polymer Fabric‖-ACI
Structural Journal.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
EXPERIMENTAL STUDIES ON VIABILITY OF USING
GEOSYNTHETICS AS FIBERS IN CONCRETE
R.Gobinath*, K.Rajeshkumar*
* Lecturer, Department Of Civil Engineering,PSNA College of Engineering and Technology
ABSTRACT
It is evident from literature review that in the recent decades the thrust for finding
an alternative to the costly steel reinforcement is increasing, several alternatives have been tested
across the globe. Some viable alternatives are found, also many techniques of replacing the steel
and addition of tensile strength to concrete is studied. The methods which are found to be cost
effective and feasible are also tried in construction in various areas. Once such alternative
technique is providing subsidiary reinforcement in the way of addition of natural or artificial
fibers to the concrete. Several fibers are also tried with concrete, some proved to be successful in
adding strength and durability to the concrete but still now many fibers are in research stage
only. Copious materials were introduced as additional fibers to concrete such as polypropylene,
glass fibers, FRP, coir etc. This paper describes an attempt made to incorporate geosynthetics, a
material is used reinforced soil as fibers in concrete. Geosynthetics are used widely aa soil
reinforcement, separators, drainage, filters and also used across the globe in various
infrastructure projects. In spite of several studies being done in Geosynthetics with soil,
Geosynthetics fiber had never been added with concrete. This paper details the attempt made to
check the viability of using geosynthetics as fibers in concrete.
Keywords: FRC, FRP, GFRC, Geosynthetics.
1. INTRODUCTION:
1.1 Fiber Reinforced Concrete
Fiber reinforced concrete (FRC) is concrete containing fibrous material which
increases its structural integrity. It contains short discrete fibers that are uniformly distributed
and randomly oriented. Fibers include steel fibers, glass fibers, synthetic fibers and natural
fibers. Within these different fibers that character of fiber reinforced concrete changes with
varying concretes, fiber materials, geometries, distribution, orientation and densities. It is true
that plain cement concrete posses a very low tensile strength. Limited ductility and little
resistance to cracking .internal micro cracks are inherently present in the concrete and its poor
tensile strength is due to the propagation of such micro cracks, eventually leading to brittle
fracture of the concrete. In the past, attempts have been made to import improvement in tensile
improvement in tensile properties of concrete members by way of using conventional reinforced
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
steel bars and also by applying restraining techniques. Although both these methods provide
tensile strength to the concrete members, they however, do not increase the inherent tensile
strength of concrete itself
In plain concrete and similar brittle materials ,structural cracks develop even before
loading ,particularly due to drying shrinkage or other causes of volume change .the width of
these initial cracks seldom exceeds a few microns, but their other two dimension may be of
higher magnitude. When loaded, the micro cracks propagate and open up, and owing to the effect
of steer‘s concentration, additional cracks form in places of minor defects .the structural cracks
proceed slowly or by tiny jumps because they are retard by various obstacles, changes of the
direction in by passing the more resistant grains in the matrix. The development of such micro
cracks is the main cause of the inelastic deformation in the concrete. It has been recognized that
the addition of small, closely spaced and uniformly dispersed fibres to the concrete would act as
a crack arrester and would substainly improve its static and dynamic properties. This type of
concrete is known as fibre reinforced concrete
Fibre reinforced concrete can be defined as composite material consisting of
mixtures of cement, mortar or concrete, uniformly dispersed suitable fibres. Continuous meshes,
woven fabrics and long wires or rod are not considered to be discrete fibres. Fiber-reinforcement
is mainly used in shotcrete, but can also be used in normal concrete. Fiber-reinforced normal
concrete are mostly used for on-ground floors and pavements, but can be considered for a wide
range of construction parts (beams, pillars, foundations etc) either alone or with hand-tied
rebar‘s. Concrete reinforced with fibers (which are usually steel, glass or "plastic" fibers) is less
expensive than hand-tied rebar, while still increasing the tensile strength many times. Shape,
dimension and length of fiber is important. A thin and short fiber, for example short hair-shaped
glass fiber, will only be effective the first hours after pouring the concrete (reduces cracking
while the concrete is stiffening) but will not increase the concrete tensile strength. A normal size
fibre for European shotcrete (1 mm diameter, 45 mm length—steel or "plastic") will increase the
concrete tensile strength. Steel is the strongest commonly-available fiber, and come in different
lengths (30 to 80 mm in Europe) and shapes (end-hooks). Steel fibres can only be used on
surfaces that can tolerate or avoid corrosion and rust stains. In some cases, a steel-fiber surface is
faced with other materials. Glass fiber is inexpensive and corrosion-proof, but not as ductile as
steel. Recently, spun basalt fiber, long available in Eastern Europe, has become available in the
U.S. and Western Europe. Basalt fibre is stronger and less expensive than glass, but historically,
has not resisted the alkaline environment of Portland cement well enough to be used as direct
reinforcement. New materials use plastic binders to isolate the basalt fiber from the cement. The
premium fibers are graphite reinforced plastic fibers, which are nearly as strong as steel, lighter-
weight and corrosion-proof. Some experimenters have had promising early results with carbon
annotates, but the material is still far too expensive for any building.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
1.2 Types of Fibres Reinforcement
1.2.1 Steel Fibre Reinforcement
Steel fibres have been used for a long time in construction of roads and also in floorings,
particularly where heavy wear and tear is expected. Specifications and nomenclature are
important for a material to be used as the tenders are invited based on specifications and
nomenclature of the items. In a work where steel fiber reinforced concrete was used for overlays
just like flooring, the following nomenclature can be adopted for concreting of small thickness.
1.2.2 Polymer Fiber Reinforced Concrete
Polymeric fibers are being used now because of their no risk of corrosion and also being cost
effective (Sikdar et al, 2005). Polymeric fibers normally used are either of polyester or
polypropylene. Polymer fiber reinforced concrete (PFRC) was used on two sites with ready mix
concrete and Vacuum dewatering process. In a site, fiber reinforced concrete was used over a
base cement concrete of lean mix of 1:4:8 (Figure 2) while in other site it was laid over water
bound macadam (WBM) (Figure 3).
When dewatered concrete it has no problem of water being coming out on surface during
compaction process but when it is done over WBM, a lot of concrete water is soaked by WBM
and thus the concrete loses the water to WBM and the water which comes out during
dewatering/compaction process is not in same quantity asin case of lean concrete. It appears that
it is better to provide base concrete than WBM as the base. The groove was made in one case
before setting of concrete and also panels were cast with expansion joints in one direction. No
cracks were observed in the direction in which expansion joints were provided assuming this is
longitudinal direction. In lateral direction, no joints were provided and the width of such panel
was about 12 m. It was later observed that cracks have developed in this direction.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
As it is known that the width of 12 m is too long for expansion/ contraction. It has been observed
that almost at about one–third of the panel width, such cracks developed i.e. size of panel from
one side is about 4 m and from other side it is about 8m. From the site observation, it is therefore
inferred that the panel should have the size of about 4m x 4m in the temperature conditions of
Delhi however small variation can also be made as per site conditions. In other case, the
contractor delayed the cutting of grooves and thereafter the area was occupied due to some
urgent requirements, the cracks in both the directions developed. The cracks were almost in line.
Later on the grooves were made through cutters. It has been observed that the distance of cracks
in one side was almost near to 4 m and on other side at about 7 to 9 m (Figure 5). Thus from this
case study also, inference can be made that grooves if made in panels of 4m x 4m, it would be
appropriate.
In both the cases, no lateral grooves were made, as working was not a problem due to use of
vacuum dewatering process. In both the cases, horizontal line cracks have been observed
indicating that the grooves in other direction are also essential. From this, it is imperative that
polymer fiber reinforced concrete should be laid in panels or grooves should be provided so that
concrete acts like in panels. Cutting grooves is easy as it can be made after casting of the
concrete. But it should not be delayed for long and should be made before concrete achieves its
desired strength. The size of panels may be kept around 4m x 4m.
1.2.3 Glass Fiber Reinforced Concrete
Glass Fiber Reinforced Concrete (GFRC) is a type of fiber reinforced concrete. Early
conventional borosilicate glass caused reduction in strength due to alkali reactivity with the
cement paste. Alkali resistant glass fibers (AR glass) were then produced resulting in long term
durability, but other strength loss trends were observed. Better durability result was observed
when AR glass is used with a developed low alkaline cement. Glass fiber concretes are mainly
used in exterior building façade panels and as architectural precast concrete. This material is very
good in making shapes on the front of any building and it is less dense than steel. ''Glass fiber
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
reinforced composite materials consist of high strength glass fiber embedded in a cementitious
matrix. In this form, both fibers and matrix retain their physical and chemical identities, yet they
produce a combination of properties that can not be achieved with either of the components
acting alone. In general fibers are the principal load-carrying members, while the surrounding
matrix keeps them in the desired locations and orientation, acting as a load transfer medium
between them, and protects them from environmental damage. In fact, the fibers provide
reinforcement for the matrix and other useful functions in fiber-reinforced composite materials.
Glass fibers can be incorporated into a matrix either in continuous lengths or in discontinuous
(chopped) lengths. The most common form in which fiber-reinforced composites are used in
structural application is called a laminate. It is obtained by stacking a number of thin layers of
fibers and matrix and consolidating them into the desired thickness. The fiber orientation in each
layer as well as the stacking sequence of various layers can be controlled to generate a wide
range of physical and mechanical properties for the composite laminate. The design of GFRC
panels proceeds from a knowledge of its basic properties under tensile, compressive, bending
and shear forces, coupled with estimates of behaviour under secondary loading effects such as
creep, thermal and moisture movement. There are a number differences between structural metal
and fiber-reinforced composites. For example, metals in general exhibit yielding and plastic
deformation whereas most fiber-reinforced composites are elastic in their tensile stress-strain
characteristics. However, the dissimilar nature of these materials provides mechanisms for high-
energy absorption on a microscopic scale comparable to the yielding process. Depending on the
type and severity of external loads, a composite laminate may exhibit gradual deterioration in
properties but usually would not fail in catastrophic manner. Mechanisms of damage
development and growth in metal and composite structure are also quite different. Other
important characteristics of many fiber-reinforced composites are their non-corroding behaviour,
high damping capacity and low coefficients of thermal expansion.
1.3 HISTORICAL PERSPECTIVE
The concept of using fibers as reinforcement is not new. Fibers have been used
as reinforcement since ancient times. Historically, horsehair was used in mortar and straw in mud
bricks. In the early 1900s, asbestos fibers were used in concrete, and in the 1950s the concept of
composite materials came into being and fiber reinforced concrete was one of the topics of
interest. There was a need to find a replacement for the asbestos used in concrete and other
building materials once the health risks associated with the substance were discovered. By the
1960s, steel, glass (GFRC), and synthetic fibers such as polypropylene fibers were used in
concrete, and research into new fiber reinforced concretes continues today.
1.3.1 Effect Of Fibers In Concrete
Fibers are usually used in concrete to control plastic shrinkage cracking and drying shrinkage
cracking. They also lower the permeability of concrete and thus reduce bleeding of water. Some
types of fibers produce greater impact, abrasion and shatter resistance in concrete. Generally
fibers do not increase the flexural strength of concrete, so it cannot replace moment resisting or
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
structural steel reinforcement. Some fibers reduce the strength of concrete. The amount of fibers
added to a concrete mix is measured as a percentage of the total volume of the composite
(concrete and fibers) termed volume fraction (Vf). Vf typically ranges from 0.1 to 3%. Aspect
ratio (l/d) is calculated by dividing fiber length (l) by its diameter (d). Fibers with a non-circular
cross section use an equivalent diameter for the calculation of aspect ratio. If the modulus of
elasticity of the fiber is higher than the matrix (concrete or mortar binder), they help to carry the
load by increasing the tensile strength of the material. Increase in the aspect ratio of the fiber
usually segments the flexural strength and toughness of the matrix. However, fibers which are
too long tend to "ball" in the mix and create workability problems. Some recent research
indicated that using fibers in concrete has limited effect on the impact resistance of concrete
materials. This finding is very important since traditionally people think the ductility increases
when concrete reinforced with fibers. The results also pointed out that the micro fibers is better
in impact resistance compared with the longer fibers.
1.3.2 BENEFITS OF FIBER REINFORCED CONCRETE
Controlled Plastic Shrinkage
Minimized Crack Growth
Reduced Permeability
Improved Surface Durability
Uniform Reinforcement In All Directions
Polypropylene fibers can
Improve mix cohesion, improving pumpability over long distances Improve freeze-thaw resistance Improve resistance to explosive spalling in case of a severe fire Improve impact resistance Increase resistance to plastic
2. DEVELOPMENTS IN FIBER REINFORCED CONCRETE
The newly developed FRC named Engineered Cementitious Composite (ECC) is 500 times more
resistant to cracking and 40 percent lighter than traditional concrete. ECC can sustain strain-
hardening up to several percent strain, resulting in a material ductility of at least two orders of
magnitude higher when compared to normal concrete or standard fiber reinforced concrete. ECC
also has unique cracking behavior. When loaded to beyond the elastic range, ECC maintains
crack width to below 100 µm, even when deformed to several percent tensile strains. Recent
studies performed on a high-performance fiber-reinforced concrete in a bridge deck found that
adding fibers provided residual strength and controlled cracking. There were fewer and narrower
cracks in the FRC even though the FRC had more shrinkage than the control. Residual strength
is directly proportional to the fiber content. A new kind of natural fiber reinforced concrete
(NFRC) made of cellulose fibers processed from genetically modified slash pine trees is giving
good results. The cellulose fibers are longer and greater in diameter than other timber sources.
Some studies were performed using waste carpet fibers in concrete as an environmentally
friendly use of recycled carpet waste. A carpet typically consists of two layers of backing
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
(usually fabric from polypropylene tape yarns), joined by CaCO3 filled styrene-butadiene latex
rubber (SBR), and face fibers (majority being nylon 6 and nylon 66 textured yarns). Such nylon
and polypropylene fibers can be used for concrete reinforcement. Polymeric fibers such as
polyester or polypropylene are being used due to their cost effective as well as corrosion
resistance though steel fibers also work quite satisfactorily for a long Fiber reinforced concrete
has advantage over normal concrete particularly in case of time. It appears that fiber reinforced
concrete should be laid on base concrete of lean mix such as 1:4:8 cement concrete rather than
over WBM and provided with grooves in panels of about 4m x 4m to avoid expansion/
contraction cracks. Grooves can be made after casting of concrete through cutters.
3. GEOSYNTHETICS:
Geosynthetics is the term used to describe a range of generally polymeric products used to solve
civil engineering problems. The term is generally regarded to encompass six main product
categories: geotextiles. Geogrids, geonets, geomembranes. Geosynthetic clay liners, geofoam
and geocomposites. The polymeric nature of the products make them suitable for use in the
ground where high levels of durability are required. Properly formulated, however, they can also
be used in exposed applications. Geosynthetics are available in a wide range of forms and
materials, each to suit a slightly different end use. These products have a wide range of
applications and are currently used in many civil, geotechnical, transportation, hydraulic, and
private development applications including roads, airfields, railroads, and embankments,
retaining structures, reservoirs, canals, dams, erosion control, sediment control, landfill liners,
landfill covers, mining, aquaculture and agriculture.
3.1 GEOTEXTILES
Geotextiles form one of the two largest groups of geosynthetic materials. Their rise in growth
during the past 30-years has been nothing short of awesome. They are indeed textiles in the
traditional sense, but consist of synthetic fibers (all are polymer-based) rather than natural ones
such as cotton, wool, or silk. Thus, biodegradation and subsequent short lifetime is not a
problem. These synthetic fibers are made into flexible, porous fabrics by standard weaving
machinery or they are mailed together in a random nonwoven manner. Some are also knitted.
The major point is that geotextiles are porous to liquid flow across their manufactured plane and
also within their thickness, but to widely varying degree. There are at least 100 specific
application areas for geotextiles that have been developed; however, the fabric always performs
at least one of four discrete functions; separation, reinforcement, filtration and/or drainage.
3.2 GEOGRIDS
Geogrids represent a rapidly growing segment within geosynthetics. Rather than being a woven,
nonwoven or knitted textile fabric, geogrids are polymers formed into a very open, grid like
configuration, i.e., they have large apertures between individual ribs in the machine and cross
machine directions. Geogrids are (a) either stretched in one or two directions for improved
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
physical properties, (b) made. On weaving or knitting machinery by standard textile
manufacturing methods, or (c) by bonding rods or straps together. There are many specific
application areas; however, they function almost exclusively as reinforcement materials.
3.3 GEONETS
Geonets, called "geospacers" by some, constitute another specialized segment within the
geosynthetics area. They are formed by continuous extrusion of parallel sets of polymeric ribs at
acute angles to one another. When the ribs are opened, relatively large apertures are formed into
a netlike configuration. Their design function is completely within the in-plane drainage area
where they are used to convey all types of liquids.
3.4 GEOMEMBRANES
Geomembranes represent the other largest group of geosynthetics and in dollar volume their
sales are even greater than that of geotextiles. Their initial growth in the USA and Germany was
stimulated by governmental regulations originally enacted in the early 1980s [5]. The materials
themselves are relatively thin impervious sheets of polymeric materials used primarily for linings
and covers of liquid- or solid- storage facilities. This includes all types of landfills, reservoirs,
canals and other containment facilities. Thus the primary function is always containment
functioning as a liquid and/or vapor barrier. The range of applications is very great, and in
addition to the geo environmental area, applications are rapidly growing in geotechnical,
transportation, hydraulic, and private development engineering.
3.5 GEOSYNTHETIC CLAY LINERS
Geosynthetic clay liners, or GCLs, are an interesting juxtaposition of polymeric materials
and natural soils. They are rolls of factory fabricated thin layers of bentonite clay sandwiched
between two geotextiles or bonded to a geomembrane. Structural integrity of the subsequent
composite is obtained by needle-punching, stitching or physical bonding. GCLs are used as a
composite component beneath a geomembrane or by themselves in geoenvironmental and
containment applications as well as in transportation, geotechnical, hydraulic, and many private
development applications.
3.6 GEOFOAM
Geofoam is a product created by a polymeric expansion process resulting in a ― foam ‖
consisting of many closed, but gas-filled, cells. The skeletal nature of the cell walls is the
unexpanded polymeric material. The resulting product is generally in the form of large, but
extremely light, blocks which are stacked side-by-side providing lightweight fill in numerous
applications. The primary function is dictated by the application; however separation is always a
consideration and geofoam is included in this category rather than creating a separate one for
each specific material.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
GEOCOMPOSITES
A geocomposite consists of a combination of geotextiles, geogrids, geonets and/or
geomembranes in a factory fabricated unit. Also, any one of these four materials can be
combined with another synthetic material (e.g., deformed plastic sheets or steel cables) or even
with soil. Collage of geosynthetic products.
3.7 BASIC CHARACTERISTICS OF GEOSYNTHETICS
● Non-corrosiveness
● Highly resistant to biological and chemical degradation
● Long-term durability under soil cover
● High flexibility
● Minimum volume
● Lightness
● Ease of storing and transportation
● Simplicity of installation
● Speeding the construction process
● Making economical and environment-friendly solution
● Providing good aesthetic look to structures
3.8 APPLICATIONS OF GEOSYNTHETICS
Geosynthetics are generally designed for a particular application by considering the primary
function that can be provided. As seen in the accompanying table there are five primary
functions given, but some groups suggest even more.
3.8.1 Separation
Separation is the placement of a flexible geosynthetic material, like a porous geotextile, between
dissimilar materials so that the integrity and functioning of both materials can remain intact or
even be improved. Paved roads, unpaved roads, and railroad bases are common applications.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Also, the use of thick nonwoven geotextiles for cushioning and protection of geomembranes is in
this category. In addition, for most applications of geofoam, separation is the major function.
3.8.2 Reinforcement
Reinforcement is the synergistic improvement of a total system ‘ s strength created by the
introduction of a geotextile or a geogrid (both of which are good in tension) into a soil (that is
good in compression, but poor in tension) or other disjointed and separated material.
Applications of this function are in mechanically stabilized earth walls and steep soil slopes.
Also involved is the application of basal reinforcement over soft soils and over deep foundations
for embankments and heavy surface loadings.
3.8.3 Filtration
Filtration is the equilibrium soil-to-geotextile interaction that allows for adequate liquid flow
without soil loss, across the plane of the geotextile over a service lifetime compatible with the
application under consideration. Filtration applications are highway under drain systems,
retaining wall drainage, and landfill leach ate collection systems, as silt fences and curtains, and
as flexible forms for bags, tubes and containers. Drainage is the equilibrium soil-to-geosynthetic
system that allows for adequate liquid flow without soil loss, within the plane of the geosynthetic
over a service lifetime compatible with the application under consideration. Geopipe highlights
this function, and also geonets, geocomposites and (to a lesser extent) geotextiles.
3.8.4 Drainage
Drainage applications for these different geosynthetics are retaining walls, sport fields, dams,
canals, reservoirs, and capillary breaks. Also to be noted is that sheet, edge and wick drains are
geocomposites used for various soil and rock drainage situations.
3.8.5 CONTAINMENT
Containment involves geomembranes, geosynthetic clay liners, or some geocomposites which
function as liquid or gas barriers. Landfill liners and covers make critical use of these
geosynthetics. All hydraulic applications (tunnels, dams, canals, reservoir liners, and floating
covers) use these geosynthetics as well.
4. PRESENT STUDY
Current study conducted at PSNA College of Engineering and Technology is a sponsored
program from a testing agency. The study aimed to check the viability of using Geosynthetics in
whole or as fibers in the concrete and also to study the strength and durability properties of the
concrete with incorporated Geosynthetics fibers. The proposed study was started on June, 2009
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
and still in the preliminary stage but majority of the viability study was conducted. Since there
are no codes or design procedures available for adding Geosynthetics fibers with concrete as a
whole experimental verification of the whole process is done with batch studies.
4.1 Study method of incorporating Geosynthetics in concrete
Initially the question was the durability of the Geosynthetics fibers in the concrete since the
reaction of cement in concrete is a chemical reaction, but it was proved in several studies that
Geosynthetics are used in any type of environment, even in marine conditions and proved to be
durable. Several types of Geosynthetics are resistant to acid attack, alkali reaction, etc which
proves them to be viable alternative fibers that can be added in concrete. Figure 6 shows the way
the Geosynthetics are added as fibers in the concrete as similar to the glass and polypropylene
fibers added to the concrete.
Figure 6 : Image showing Geosynthetics fibers mixed with concrete.
There are several ways to add the Geosynthetics fibers to concrete as listed below
1. Addition of Geosynthetics as small fibers in the fresh concrete
2. Addition of Geosynthetics as small pieces instead of fibers in the concrete
3. Addition of large length of Geosynthetics in the direction perpendicular to the load
application in the structural members.
4. Combination of the above mentioned methods.
Figure 7 shows the image of the type of Geosynthetics used in the studies, the sample is cut into
15 cm X 15 cm piece and added in the concrete cubes and also as 10 X 10 X 50 cm piece and
added in three layers in the beams. Beams are also cast with one layer and two layer of
Geosynthetics to check the viability of addition of Geosynthetics.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Figure 7 : Image showing the types of Geosynthetic used in concrete
There are several types of Geosynthetics available in the market and the current study
also aims to find the best suitable Geosynthetics which can be impregnated in the concrete. Few
of them cannot be used in the concrete due to their brittle nature but they can be used as
supporting reinforcement in several areas such as beam column joints or surrounding the
columns instead of tie ups since they take load uniaxially. Figure 8 shows the image of a type of
Geonet used in the studies with cylinder specimens.
Figure 7: Image showing Geonet and Geogrid
Test specimens were cast with the M20 concrete mix and M15 concrete mix after doing
mix design for arriving the quantity of the components of concrete. The water cement ratio is
fixed as 0.5 for initial studies, further studies are proposed with varying water cement ratio in
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
high strength concrete. Separate specimens are cast for testing on 7 days, 28 days strength as per
code requirements and the test results are given below.
4.2 TEST RESULTS AND DISCUSSION:
Several tests were conducted for testing the quality of the Geosynthetics used and the properties
were found to be quite satisfactory for using it with concrete, the tensile strength and durability
of the Geosynthetics used were found to be good enough. Figure 8 shows the Geosynthetics
being cut for adding into the specimens casted.
Figure 8 : Image showing Geosynthetics being prepared for adding into concrete
The following test are conducted on aggregates they are listed below and table 1 shows the
results obtained in various initial tests conducted
1. Specific gravity
2. Crushing test for aggregate
3. Abrasion test
4. Soundness test
5. Fineness test
6. Impact test aggregate.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Table 1 : Test results of various test conducted
S. No TEST CONDUCTED RESULTS
1 Specific gravity of fine aggregate 2.66
2 Specific gravity of coarse aggregate 2.78
2 Crushing value of Coarse aggregate 24%
3 Abrasion value of Coarse aggregate 25.5%
4 Aggregate Impact value of Coarse aggregate 28%
5 Fineness Test on fine aggregate 2.66
6 Test for Soundness of Coarse aggregate 14%
7 Mix design used 1:2:4
8 Slump Value of fresh concrete without fibers 160 mm
9 Slump Value of fresh concrete with fibers 110 mm
10 Flexure strength test on hardened concrete
without Geosynthetics
0.86 N/mm2
11 Flexure strength test on hardened concrete with
Geosynthetics
1.2 N/mm2
12 Compressive Strength in alternate orientation
on hardened concrete without Geosynthetics
16 N/mm2
13 Compressive Strength in alternate orientation
on hardened concrete with Geosynthetics
17 N/mm2
The fine aggregate and coarse aggregate are graded properly before using it with the concrete
and the results obtained in workability are found to be satisfactory. Moderate vibration were used
using vibratory table for compacting the concrete in the moulds, it was found that bleeding
occurs in the concrete added with Geosynthetics fibers to a large quantity. Initial studies proved
that the Geosynthetics fibers may not allow the concrete to mix properly in the layer it was
spread, few small holes were made on the surface of the Geosynthetics to allow the bonding of
concrete.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
4.3 Viability Studies
To check the durability of Geosynthetics in concrete two types of tests were conducted
Mortar cudes of size 70mm X 70 mm X 70 mm was prepared without and with
Geosynthetic fibers in the direction perpendicular to the applied load.
Geosynthetics fibers ( various types) are added with cement paste of good consistency
and cured for 30 days to check the durability of fibers
The study results proved that it is feasible to use Geosynthetics with concrete and the cement
reaction while setting and heat of hydration is not affecting the fibers. The Geosynthetics are
removed from the cement paste set and studied under Electron microscope compared with the
original fibers. It shows that small disorientation of fibers with non polymer based Geosynthetics
but polymer and plastic based Geosynthetics resist the action of cement and there are no notable
changes from original.
4.4 Strength Studies
To check the increase in strength by addition of Geosynthetic fibers control specimens were cast
with 1:2:4 ratio of required amount and tested, the initial tests conducted on the control
specimens gave the confidence that the introduction of Geosynthetics may increase the strength.
It is decided to study Flexure and compression strength initially, beam and cube specimens were
casted as per IS 516 of required number with varying Geosynthetic proportion and type of
Geosynthetic and tested. Figure 9 shows the Geosynthetics added in the beam specimen casted
for flexure testing.
Figure 9 : Image showing the Geosynthetics added in the beam specimen
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
All the test specimens were cured for required period of time in quality water without chloride
content or any other harmful impurities present. Figure 10 shows the way the Geosynthetics are
added in the concrete cube and cylinders.
Figure 10: Image showing addition of Geosynthetics fibers in specimen
The studies were conducted in the compression testing machine and flexure testing apparatus, the
results found to be there is an increase of nearly 30% in the load carrying capacity of the beam
and cube members after the addition of Geosynthetics. Further testing is going on to find the
splitting tensile strength with varying proportion of fibers in the concrete.
5. CONCLUSION
Fiber-reinforced concrete weighs much less than regular concrete--as much as 75
percent less in some cases. This allows for reduced shipping costs. GFRC has a very high
strength-to-weight ratio and can be used to make complex shapes, since it is reinforced
internally. It can also be sprayed into forms and molds, making better finished products, as there
is no chance for air bubbles to form. It also does not crack as easily as regular cement and does
not chip when it is cut. It is found from the studies conducted that the Geosynthetics can be used
as a whole in the concrete or also as fibers in the concrete for adding strength and durability of
concrete. Geosynthetics are available plenty in the market and the cost per Square meter is less
than Rs.60 which makes it as an economical choice also. The strength and durability of concrete
using Geosynthetic is to be studied further for arriving into any conclusion but initial studies
proved the viability of using them in tandem with other constituents of concrete.
6. RFERENCES
IS: 14324 (1995) Indian Standard for geotextiles—methods of test for determination of
water permeability/permittivity. Bureau of Indian Standards, New Delhi
IS: 14706 (1999) Indian standard for geotextiles—sampling and preparation of test
specimens. Bureau of Indian Standards, New Delhi.
IS 516: 1959 Method of test for`strength of concrete
IS 2386 ( Part I-VIII): 1963- Methods of Test for Aggregates for Concrete
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
EXPERIMENTAL STUDIES ON REDUCING THICKNESS OF FLEXIBLE
PAVEMENTS BY USING WOVEN AND NON-WOVEN GEOSYNTHETICS IN
SUBSURFACE
R.Gobinath*, K.Rajeshkumar*
* Lecturer, Department Of Civil Engineering,PSNA College of Engineering and
Technology
ABSTRACT
Pavement or Road surface is the durable surface material laid down on an area intended to
sustain traffic (vehicular or foot traffic), such surfaces are frequently marked to guide traffic. The
most common modern paving methods are asphalt and concrete. in the past, brick was
extensively used, as was metalling. today, permeable paving methods are beginning to be used
more for low-impact roadways and walkways. Bountiful research works have been done in the
area of designing of pavements by many methods, the value arrived finally will be the thickness
of various layers of payment. If there arise a need to reduce the thickness of pavement it is
mandatory to introduce some reinforcing material should be introduced in the pavement to
increase its strength. Many materials, fibres, composites were tried as reinforcing material for
both flexible and rigid pavements and several researches being done to identify newer cost
effective and better material. Geosynthetics proved to be a great choice of such a material and it
was applied in many projects successfully. Various types of Geosynthetics were tried in the
pavements and found to be exultant in reducing the thickness of the pavements which leads to
considerable cost savings. This paper describes various methods of flexible pavement design and
also describes the way the Geosynthetics can be used to reduce pavement thickness. A detailed
case study was proved to give clear picture about how the thickness of the pavement reduces
when Geosynthetics are used in the soil. Geosynthetics both woven and Non-woven can be tried
with various types of soils depending on the soil stability and other parameters but it was widely
practiced using of Geonets and Geogrids for reinforcing the soil which also found to be
satisfactory in reducing pavement thickness.
Keywords: Flexible pavement, Geosynthetics, CBR method.
1. INTRODUCTION
A road or pavement is an identifiable route, way or path between places Roads are
typically smoothed, paved, or otherwise prepared to allow easy travel though they need not be,
and historically many roads were simply recognizable routes without any formal construction or
maintenance. The formation of network of roads is unavoidable irrespective of the soil
conditions by the development of the civilization. Because the civilization needs better
transportation facilities and hence the pavements need to be strong enough to be durable. If an
attempt is made to from a pavement on a very weak subgrade soil then the pavement thickness
will be enormously large. This in turn will increase the cost so several attempts has been made to
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
strengthen the subgrade soil itself to reduce the cost of construction conventional methods of
improving the soil subgrade is by compaction or by using stabilization agents such as cement,
lime, fly ash, bitumen etc, depending upon the property of subgrade soil to be improved. Even
though for thousands of years man has been modifying soil by adding extraneous materials to it.
The idea of using textiles for the purpose is just a few decades old. Geotextiles made from
synthetic fibers were first used in Netherland that was in 1953. Concrete pavements (specifically,
Portland cement concrete) are created using a concrete mix of Portland cement, gravel, and sand.
The material is applied in a freshly-mixed slurry, and worked mechanically to compact the
interior and force some of the thinner cement slurry to the surface to produce a smoother, denser
surface free from honeycombing.
1.1 Concrete Pavements
Concrete pavements are also used widely which have been refined into three common
types: jointed plain (JPCP) jointed reinforced (JRCP) and continuously reinforced (CRCP). The
one item that distinguishes each type is the jointing system used to control crack development.
Jointed Plain Concrete Pavements (JPCP) contains enough joints to control the location of all the
expected natural cracks. The concrete cracks at the joints and not elsewhere in the slabs. Jointed
plain pavements do not contain any steel reinforcement. However, there may be smooth steel
bars at transverse joints and deformed steel bars at longitudinal joints. The spacing between
transverse joints is typically about 15 feet for slabs 7-12 inches thick. Today, a majority of the
U.S. state agencies build jointed plain pavements.
1.2 Jointed Concrete Pavements
Jointed Reinforced Concrete Pavements (JRCP) contains steel mesh reinforcement
(sometimes called distributed steel). In jointed reinforced concrete pavements, designers increase
the joint spacing purposely, and include reinforcing steel to hold together intermediate cracks in
each slab. The spacing between transverse joints is typically 30 feet or more. In the past, some
agencies used a spacing as great as 100 feet. During construction of the interstate system, most
agencies in the Eastern and Midwestern U.S. built jointed-reinforced pavement. Today only a
handful of agencies employ this design, and its use is generally not recommended as JPCP and
CRCP offer better performance and are easier to repair.
1.3 Continuously Reinforced Concrete Pavements
Continuously Reinforced Concrete Pavements (CRCP) do not require any transverse
contraction joints. Transverse cracks are expected in the slab, usually at intervals of 3-5 ft. CRCP
pavements are designed with enough steel, 0.6-0.7% by cross-sectional area, so that cracks are
held together tightly. Determining an appropriate spacing between the cracks is part of the design
process for this type of pavement. Continuously reinforced designs generally cost more than
jointed reinforced or jointed plain designs initially due to increased quantities of steel. However,
they can demonstrate superior long-term performance and cost-effectiveness. A number of
agencies choose to use CRCP designs in their heavy urban traffic corridors.One advantage of
cement concrete roadways is that they are typically stronger and more durable than asphalt
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
roadways. They also can easily be grooved to provide a durable skid-resistant surface.
Disadvantages are that they typically have a higher initial cost and are perceived to be more
difficult to repair.
1.4 TYPES OF PAVEMENTS
1.4.1 Flexible Pavements
This pavement consist of a relatively thin wearing surface built over a base course and
subbase course and they rest upon the compacted subgrade. The thickness of the flexible
pavement is meant to include all components of the pavement above the compacted subgrade.
Thus subgrade, base and wearing surface are the structural components of the pavement. Flexible
pavements are so named because the total pavement structure deflects, or flexes, under loading.
A flexible pavement structure is typically composed of several layers of material. Each layer
receives the loads from the above layer, spreads them out, then passes on these loads to the next
layer below. Thus, the further down in the pavement structure a particular layer is, the less load
(in terms of force per area) it must carry. A true flexible pavement yields ―elastically‖ to traffic
loading and is constructed with a bituminous-treated surface or a relatively thin surface of hot-
mix asphalt (HMA) over one or more unbound base courses resting on a subgrade. Its strength is
derived from the load-distributing characteristics of a layered system designed to ultimately
protect each underlying layer including the subgrade from compressive shear failure.
Progressively better materials are used in the upper structure to resist higher near-surface stress
conditions caused by traffic wheel loads and include an all-weather surface that is resistant to
erosion by the environment and traffic action. The bituminous surface layer must also be
resistant to fatigue damage and stable under traffic loads when temperatures are in excess of
150ºF. The figure 1 shows the typical section of a flexible pavement
Figure 1: Section showing a typical Flexible pavement
1.4.2 Rigid Pavement
Rigid pavements are made up of Portland cement concrete and may or may not have a base
course between the pavement and subgrade. In this type of pavement, the concrete exclusive of
the base is referred to as the pavement. A rigid pavement structure is composed of a hydraulic
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
cement concrete surface course, and underlying base and subbase courses (if used). Another term
commonly used is Portland cement concrete (PCC) pavement, although with today‘s pozzolanic
additives, cements may no longer be technically classified as ―Portland.‖
The surface course (concrete slab) is the stiffest and provides the majority of strength. The base
or subbase layers are orders of magnitude less stiff than the PCC surface but still make important
contributions to pavement drainage, frost protection and provide a working platform for
construction equipment.
Rigid pavements are substantially ‗stiffer‘ than flexible pavements due to the high modulus of
elasticity of the PCC material resulting in very low deflections under loading. The rigid
pavements can be analyzed by the plate theory. Rigid pavements can have reinforcing steel,
which is generally used to handle thermal stresses to reduce or eliminate joints and maintain tight
crack widths. The figure 2 shows the typical section of rigid pavement
Figure 2: Section showing a rigid pavement
1.4.2.1 Surface Course
The surface course is the layer in contact with traffic loads and normally contains the highest
quality materials. It provides characteristics such as friction, smoothness, noise control, rut and
shoving resistance and drainage. In addition, it serves to prevent the entrance of excessive
quantities of surface water into the underlying base, subbase and subgrade (NAPA, 2001). This
top structural layer of material is sometimes subdivided into two layers (NAPA, 2001):
1.4.2.2 Wearing Course.
This is the layer in direct contact with traffic loads. It is meant to take the brunt of traffic wear
and can be removed and replaced as it becomes worn. A properly designed (and funded)
preservation program should be able to identify pavement surface distress while it is still
confined to the wearing course. This way, the wearing course can be rehabilitated before distress
propagates into the underlying intermediate/binder course.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Intermediate/Binder Course. This layer provides the bulk of the HMA structure. It's chief
purpose is to distribute load.
1.4.2.3 Base Course
The base course is immediately beneath the surface course. It provides additional load
distribution and contributes to drainage and frost resistance. Base courses are usually
constructed out of:
1.4.2.4 Aggregate
Base courses are most typically constructed from durable aggregates (see Figure 2.5) that will
not be damaged by moisture or frost action. Aggregates can be either stabilized or unstabilized.
HMA. In certain situations where high base stiffness is desired, base courses can be constructed
using a variety of HMA mixes. In relation to surface course HMA mixes, base course mixes
usually contain larger maximum aggregate sizes, are more open graded and are subject to more
lenient specifications
1.4.2.5 Subbase Course
The subbase course is between the base course and the subgrade. It functions primarily as
structural support but it can also:
Minimize the intrusion of fines from the subgrade into the pavement structure.
Improve drainage.
Minimize frost action damage.
Provide a working platform for construction.
The subbase generally consists of lower quality materials than the base course but better than the
subgrade soils. A subbase course is not always needed or used. For example, a pavement
constructed over a high quality, stiff subgrade may not need the additional features offered by a
subbase course so it may be omitted from design. However, a pavement constructed over a low
quality soil such as a swelling clay may require the additional load distribution characteristic that
a subbase course can offer. In this scenario the subbase course may consist of high quality fill
used to replace poor quality subgrade (over excavation).
2. DESIGN OF FLEXIBLE PAVEMENT
The flexible pavements are built with number of layers. In the design process, it is to
be ensured that under the application of load none of the layers is over-stressed. The maximum
intensity of load stresses occurs in the layer of the pavement. The magnitude of load stresses
reduces at lower layers. Hence superior pavement materials are used in top layers of flexible
pavements.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
2.1 METHODS OF FLEXIBLE PAVEMENT DESIGN
Various approaches of flexible pavement design may be classified into three broad groups,
namely,
(i) Empirical methods,
(ii) Semi-empirical or semi theoretical method
(iii) Theoretical method.
Various design methods of flexible pavement
(i) Group index method
(ii) California bearing ratio methods
(iii) California R-value or stabilometer methods
(iv) Triaxial test method
(v) Menold method
(vi) Burmister method
2.2 Use Of Geotextils In Pavements
In recent years geotextiles are reported to have played a prominent role in road works in the
developed countries. The case histories have shown the geotextiles in road construction .
(i) Allow 25% reduction in the base coarse aggregate.
(ii) Increase the life of the pavement.
(iii) Reduce the maintenance cost.
An attempt has been made to solve the above-mentioned problem of forming a pavement over a
weak subgrade soil by the use of geotextiles reinforcement. It is found from many studies that
Once of the challenging problems controlling the engineer is the construction of roads
over very soft and loose soil –strata with low bearing strength.
It is also essential to protect the subgrade from penetration in order to retain the
strength of the soil upon which the final construction may be dependent and at some
time to construct an efficient and economic pavement.
Recently a new concept of use of fabrics in road construction has been employed
between subgrade and sub base of flexible pavement constructed over soils of low
bearing capacity.
Now a day‘s synthetic fabrics called geotextiles have been found tobe more economical, very
easily to handled, stronger and longer lasting then many traditionally used materials hither to
used. These fabrics resist a large range of acid in basic soil and liquids as well as biological
attack.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
2.2.1 Geosynthetics in HMA Applications
The primary purpose of incorporating geosynthetics in the pavement design process is to reduce
reflective cracking in HMA overlays and to resist moisture intrusion into the underlying
pavement structure. Geosynthetics can be part of an overall rehabilitation strategy that will as a
minimum include the placement of a new wearing/surface course of HMAC. One concern that
the geosynthetic users should keep in mind is future rehabilitations as any anticipated milling of
HMAC layers must avoid RAP contamination and possible fouling of milling equipment.
2.2.1.1 Geogrids
The main function of a geogrid in an HMA application is to retard the occurrence of reflective
cracking. In evaluating the appropriateness of use, cracking in the existing structure should be
limited to cases in which the crack faulting does not fluctuate significantly with traffic loading
and crack width does not fluctuate significantly with temperature differentials.
The pavement should be structurally sound with existing cracks limited to less than 3/8‖ width.
Hence, low to moderate levels of alligator cracking, or random cracking may benefit from
application of grids in HMA, whereas widely spaced thermal cracking or underlying
rocking/faulted PCC slabs will probably not benefit. It is necessary to repair localized highly
distressed/weak areas and apply a levelup course of HMAC prior to applying the geogrid.
Where rutting exceeding ½-inch exists, milling prior to applying the level-up should be
considered. A minimum 2.0-inch surfacing course over the grid is recommended. Installation of
this type of product has proven to be problematic and will result in premature failure (fatiguing)
of the surfacing overlay where a lack of bonding (surface to grid to levelup) occurs. It is highly
recommended that the manufacturer‘s installation procedures be strictly followed and that a
manufacturer‘s representative be present during the planning and construction process.
2.2.1.2 Fabrics, composites, and membranes
These products provide a moisture barrier in addition to varying degrees of resistance to
reflective cracking. Application guidelines are similar to those recommended above for the
geogrid. The impermeable qualities of these products can be a double-edged sword in that they
prevent trapped moisture within the structure from transpiring out. This may result in debonding
of HMA layers and/or stripping of HMA layers below the product, especially if the lower mixes
are moisture susceptible. Also, if the surfacing overlay is permeable and surface moisture can not
readily escape the section laterally (mill and inlay technique is especially prone), stripping of the
surface mix may also occur. It is incumbent upon users of these products to insure laboratory
testing is performed to determine HMAC stripping susceptibility of existing mixes (highway
cores) and the proposed level-up and overlay mixes.
2.2.2 Geosynthetics in Pavement Bases (non-HMA Applications)
Geosynthetics are placed in pavement bases to perform one or more of the following functions:
reinforcement, separation, and filtration. Base reinforcement results from the addition of a
geogrid or composite at the bottom or within a base course to increase the structural or load-
carrying capacity of a pavement system by the transfer of load to the geosynthetic material. The
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
primary mechanism associated with this application is lateral restraint or confinement of
aggregates in the base. Where very weak subgrades exist, geosynthetics can increase the bearing
capacity by forcing the potential bearing capacity failure surface to develop along alternate,
higher strength surfaces. Geogrids may also be considered for use in locations where chemical
stabilization of the subgrade is not desirable due to possible reaction with sulfates in the
subgrade, or not practical because of expedited construction concerns, particularly in urban
settings.
There have been assertions that the resultant increase in restraint or confinement should allow for
design of thinner structures using these products versus structural designs which do not, however
their benefits may only be noticeable over the long term and there appears to be an absence of
long-term controlled monitoring. For purposes of geosynthetic reinforcement, CSP M&P
recommends that their application be viewed as an ―insurance policy‖ rather than a ―modulus-
multiplier‖ or structure-reducing product.
Geosynthetics used for separation have classically been applied to prevent subgrade soil from
migrating into the unbound base (or subbase), or to prevent aggregates from an unbound base (or
subbase) from migrating into the subgrade. A small amount of fines introduced into the granular
base can significantly reduce the internal friction angle and render the flex base weaker. Potential
for these circumstances increases where wet, soft subgrades exist. Typically a geocomposite will
be used for this application, placed at the subgrade/unbound base interface.
Geotextile separators act to maintain permeability of the base materials over the life of the
section, and they allow the use of more open-graded, free-draining base and subbase materials.
Another form of separation is being increasingly explored where there is a high potential for
reflective cracking originating in the subgrade or chemically-bound base. A grid or composite is
used to dissipate stresses induced by the opening crack. Longitudinal edge cracking is
particularly an issue in areas where moderate to high PI soils are exposed to prolonged cycles of
wetting and drying. Geogrids will typically be employed at the subgrade/bound base interface, or
if a flex base is placed above a bound base (e.g., FDR projects), the grid may be placed at this
location. Grids should be a minimum of 10-ft. wide to reduce the potential for longitudinal
cracking due to edge drying. The function of filtration is to allow for in-pavement moisture
transfer but restrict movement of soil particles, hence composites or fabrics that are placed for
the classical purpose of separation will usually incorporate this function as well. It prevents the
penetration of subgrade soil into the sub base and checks the movement of aggregate into the
subgrade under the traffic. It also allows the dissipation of pore water pressure.
3. CASE STUDY
Under this investigation an attempt was made to examine the influence of woven fabric of
polypropylene geotextile on the improvement of performance and life of pavement over the
weaker subgrades. CBR test with this material embedded in the subgrade soil has been carried
out both in soaked and unsoaked conditions. The sample is selected for investigation is from a
weak subgrade near kulathur. The selected sample is tested for its varies properties. Its CBR
value has been determined in both soaked and unsoaked condition. Then an attempt has been
made to improve the CBR value by geotextile reinforcement.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
3.1 Properties Of Geotextile Used
Code 0550 A
Material polypropylene(woven)
Weight per sq.mt is 200 gms
Breaking strength – 110 Kg in length direction 60 Kg in width direction(determined in 5
cm*20 cm strip)
Thermal stability – 0 c to 100 c
Air permeability – 20.5 m * 3/min/sq.m
Thickness – 0.8 mm
Water permeability at 50 mm water head 50 lit/sec/m2
Resistant to UV radiation
Resistant to chemical action
Resistant to biological degradation
3.2 Properties Of The Soil Sample Selected
To determine the particle size distribution approximately dry mechanical analysis has been
carried out and various laboratory tests were conducted to find the properties of soil to be used
and its results are expressed in table 1.
Table 1: Properties of Soil to be used in the design
1 Effective size 0.18 mm
2 Uniformity coefficient 9.4
3 Specific gravity 2.66
4 Liquid limit 60%
5 Plastic limit 45%
6 shrinkage limit 10.50%
7 Plasticity index 15%
8 Flow index 19.40%
9 Toughness index 0.79
10 Shrinkage ratio 2.3
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
3.3 Experimental Results
To determine the CBR values, the samples are compacted at 100% standard proctor
density with optimum moisture content of 8% which is taken from figure 3. The CBR test has
been carried out in the unsoaked condition in the selected sample and the load in Kg for various
penetrations has been noted as in 6.4. From the load for 2.5 and 5mm penetration the CBR values
has been calculated on below;
%CBR at 2.5 mm penetration=235/1370*100=17.1%
%CBR at 5 mm penetration =400/2055*100=195%
The CBR value at 5mm penetration has been selected for the design of pavement thickness. Then
the same sample is compacted at 100%poroctor density and is soaked in water for 96 hours with
all the strain gauges arrangements to measure the expansion ratio is noted as 13.69% For the
soaked sample the load in kg for various penetration has been noted in fig 6.5. From the load for
2.5 mm and 5 mm penetration the CBR value has been calculated as below:
%CBR at 2.5 mm penetration = 25.6/1370*100 = 1.9%
%CBR at 5.0 mm penetration = 328/2055*100 = 1.6%
It has been noted that the CBR value at 2.5 mm penetration is higher and it has been selected for
the design purpose. To study the influence of geotextiles in the improvement of the CBR value,
the geotextiles is placed at the top one third interface in the CBR mould. Then the CBR test has
been carried in the unsoaked condition compacted at 100% density to determine the load for
various penetrations as shown in the figure.
From the loads for 2.5 and 5.0mm penetration,the CBR value has been calculated
%CBR at 2.5 mm penetration =390/1370*100 =28.5%
%CBR at 5.0 mm penetration =550/2055*100 =26.8%
It has been noted that the CBR value at 2.5 mm penetration is higher. Hence this CBR value is
selected for the design of pavement thickness. Then the same sample is compacted at 100%
proctor density with geotexile reinforced is soaked in water for 96 hours with all the strain
gauges arrangement to measure expansion ratio is measure as 12.61%. Then the same mould is
placed under the CBR load frame to determine the load for various penetrations as in the figure.
Form the loads for 2.5 to 5.0mm penetration in the CBR value has been calaulated as below:
%CBR at 2.5 mm penetration = 40.5/1370*100= 2.9%
%CBR at 5.0 mm penetration = 51/1370*100= 2.5%
It has been noted that the CBR value of 2.5 mm penetration is higher. Hence the CBR value at
2.5 mm penetration is taken for design purpose.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
4. PAVEMENT DESIGN
To determine the total pavement thickness above the subgrade in flexible pavement,
from the CBR test results the following formula devoloped by U.S corporations of engineers has
been used, if the CBR value is less than 12%
T=sqrt(p)[(1.75/CBR-1/6P*3.14)]^0.5
where,
T = Pavement thickness in cm
P = wheel load in kg
CBR= california bearing ratio in %
P = Tyre pressure in kg/m^2
For the determination of pavement thickness the following factors have been assumed.
Wheel load = 4100 kg
Tyre pressure = 6kg/cm^2
Intensity of traffic = 2000 commercial vehiles per day
Pavement thickness without geotextiles in soaked condition is arrived as
T = sqrt(4100)[(1.75/1.79)-(1/6*3.14)]^0.5
= 59.7 cm
Pavement thickness with geotextiles in soaked condition is arrived as
T = sqrt(4100)[(1.75/2.9)-(1/6*3.14)]^0.5
Pavement thickness without geotextiles in unsoaked condition
CBR value exceeding 12% the CBR design chart recommented by IRC has been used. Since the
intensity of traffic is 2000 commercial vehiles per day. The f curve has been selected,from the
chart, the thickness required for a CBR of 19.5% = 21 cm.
Pavement thickness with geotextiles in unsoaked condition
CBR design chart recmmented by the IRC has been used. From the chart, the required thickness
for a CBR of 28.5% = 16 cm. Table 2 shows the summary of results obtained in the design.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Table 2 : Table showing summary of design results
Unsoaked condition Soaked conditon
Without
geotextie
With
geotextile
Without
geotextie
With
geotextile
%CBR 19.5 28.5 1.9 2.9
Pavement thickness
in cm
21 16 59.7 47.5
Reduction in
thickness
_ 5 _ 12.2
4.1 Discussion of Results
The Load vs Penetrations curves with and without geotextiles reinforcement have been shown in
the annexure for soil compacted in maximum dry density in both soaked and unsoaked condition.
It has been observed that using a woven fabric of polypropylene, in unsoaked condition the
pavement thickness is reduced by 5 cm and soaked condition reducing in pavement thickness is
12.2 cm. Since the weakest codition is the soaked condition, the reducing in thickness of 12.2 cm
will be effective in practical. This design study clearly shows the by using Geosynthetics in the
subsurface a considerable thickness of the flexible pavement can be reduce which in turn save
cost of construction. The cost of Geosynthetics compared to the amount saved by the reduced
thickness is bare minimum and also Geosynthetics are widely available in the market making it a
viable soil reinforcing agent.
5. CONCLUSION
It has been observed that a significant reduction is obtained in thickness of pavement
when weak soil (CBR<3) is reinforced with geotextile. But for higher values of CBR (around 15)
the reduction is insignificant this justifies the use of Geotextiles reinforcement for weak sub-
grades. Hence the effectiveness of polypropylene Geotextiles in reducing the thickness of a
pavement is a significant one. It can be used as a better substitute for other strength improvement
techniques such as stabilization. It has been concluded that even a very weak subgrade can also
be used as a substratum for national highways by reinforcing the subgrades using polypropylene
Geotextiles of woven type, Geonets and Geomembranes can also be used for increasing the
strength of subsurface effectively. It has been observed on the roads constructed with Geotextiles
that the maintenance cost and the cost of construction both are taken into account the use of
geotextile may be economically viable for weak soils.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
ACKNOWLEDGEMENT
Authors wishes to thank the Chairperson, Directors and Principal of PSNA College of
Engineering and Technology for providing the opportunity of working with Geosynthetics, also
thank MODROBS, AICTE for sponsoring such a nice laboratory and other facilities to learn
about Geosynthetics and its application. They also like to submit their sincere thanks to
Dr.N.Mahendran, Ph.D., Professor and Head for supporting in the guidance and support
offered in this project in various levels.
6. REFERENCES
1. Vengatappa rao and suryanarayana raja(G.V.S) ―ENGG with geosynthetics‖ Tata
McGraw - hill, NEW DELHI.
2. Yoder .E.J: ―John Wiley‘s sons, NEW YORK‖
3. Vengatappa rao.G, Gupta.K.K and Singh P.B ―Laboratory studies on geotetiles as
reinforcement in road pavement‖
4. Khanna.S.K and Justo.C.E.G.Highway Engg
5. R M Koner. ‗Construction and Geotechnical Engineering Using Synthetic
6. Fabrics.‘ A Wiley -Interscience Publication, January, 1980.
7. V S Rajan. ‗Prospects for Geotextile Applications in India.‘ Third National
8. Convention of Textile Engineering Division and National Seminar on Nonwoven and
9. Geotextiles, organized by The Institution of Engineers (India), Baroda, 1988, pp 77-
91.
10. N N Shah and S Bhattacharya. ‗Test Method Used in Evaluation of Geotextiles
11. Fabrics.‘ Third National Convention of Textile Engineering Division and National
Seminar
12. on Nonwoven and Geotextiles, organized by The Institution of Engineers (India),
Baroda,
13. 1988, pp 108-128
14. Robert Koerner. ― Geosynthetics and its engineering applications‖ Mcgraw Hill
Edition, 1985.
15. Hawthorne, W. R.: The early development of the Dracone flexible barge. Proc. Inst.
Mech. Eng. London 175, 52--83 (1961)
16. Hsieh, J.-C., Plaut, R. H., Yucel, O.: Vibrations of an inextensible cylindrical
membrane inflated with liquid. J. Fluids Struct. 3, 151-163 (1989).
17. Bahder, T. B.: Mathematica for scientists and engineers. Reading: Addison Wesley
1995
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
USE OF SAWDUST ASH IN CONCRETE AS PART REPLACEMENT OF SAND
M. Mageswari*1
, Dr.B.Vidivelli2
*1Research Scholar, Structural Engineering, Annamalai University, Annamalai nagar, 600 002,
Tamilnadu, India.
e-mail: [email protected] 2Professor of Structural Engineering, Annamalai University, Annamalai nagar, 600 002,
Tamilnadu, India.
e-mail: [email protected]
ABSTRACT
Concrete is the most widely used construction material in the recent years. Concrete
strength is influence by the quality of sand, coarse aggregate and cement. The challenge of the
civil engineering community in future will be to execute projects in harmony with the nature
using the concept for sustainable development involving the use of high performance, economic
friendly materials produce at free of cost with the lowest possible environment impact. In the
context of the predominant building material concrete it is necessary to identify less expensive
substitute and competitive to conventional concrete. In the recent years the cost of sand has
become high because of non-availability in the near by construction site and the government had
restricted not to remove the sand form seashore areas. Sawdust ash represents a major
component of solid waste. To deal with these problems, new material concrete was developed:
Sawdust ash concrete. This paper deals with the study of sawdust ash replacing sand at different
proportions in concrete for 7, 14, 28 and 45 curing. The compressive strength of concrete are
studied by replacing the sand with 0, 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50 percentages of
sawdust ash with superplastizer. A comparison is made with the test results of normal concrete.
SEM (scanning electron microscopy) together with EDS (energy dispersive spectroscopy) is a
versatile tool which can use to image samples. Scanning electron microscope imaging facilities
identification of sand and sawdust ash constituents with greater contrast, and greater spatial
resolution than for optical methods and provide ancillary capability for element analysis and
imaging. Scanning electron microscopy analysis of the sand and sawdust ash is compared.
Key Words: Sawdust ash, scanning electron microscopy, energy dispersive spectroscopy,
compressive strength
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
1. INTRODUCTION
During the last decades it has been recognized with growing sawdust ash waste are of
large volume and that this is increasing year by year in the household , mills and factory‘s. Now
a days even in rice mills they are using sawdust for burning due to shortage of rice husk. In
Chidambaram a huge quantity of sawdust ash waste is produced in the near by rice mills and
households are dumped. On the other hand, one bucket of sawdust cost Rs 6.00 and we get
sawdust ash with no cost. The need for housing are estimated more cost and some construction
materials like natural sand are becoming rare. This waste storage disposals are becoming a
serious environmental problem especially for Chidambaram place disposal sites are lacking.
Hence there is a need for recycling more and more waste materials.
The most widely used fine aggregate for the making of concrete is the natural sand mined
from the riverbeds. However, the availability of river sand for the preparation of concrete is
becoming scarce due to the excessive nonscientific methods of mining from the riverbeds,
lowering of water table, sinking of the bridge piers, etc. are becoming common treats. The
present scenario demands identification of substitute materials for the river sand for making
concrete. The choice of substitute materials for sand in concrete depends on several factors such
as their availability, physical properties, chemical ingredients etc. In this paper, an attempt is
made on the use of sawdust ash as a part replacement of sand for the production of concrete.
Material Used
Cement: Ordinary Porland cement of 53 grades having specific gravity of 3.10 was used.
Sand: The sand used for the study was locally available river sand conforming to grading zone
III of IS: 383-1970.
Gravel: The coarse aggregate was a normal weight aggregate with a maximum size of 20mm IS:
456-2000.
Sawdust ash: The SDA used for this study was collected from the rice mills points in
Chidambaram taluk at Cuddalore District.
Mix proportion: The control mix of the concrete was designed with a mix ratio of cement /water
/Sand /Coarse of 1:0.48:1.66:3.61 by weight. The slump has maintained 30-40mm.
2. EXPERIMENTAL INVESTIGATION
Specific gravity
The results specific gravity of sand and sawdust ash mixture is given in Table 1.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Paramet
er
San
d
Coar
se
SD
A
(S+10%S
DA)
(S+20%S
DA)
(S+30%S
DA)
(S+40%S
DA)
(S+50%S
DA)
Specific
gravity
2.6
5
2.7 2.5 2.67 2.6 2.61 2.55 2.54
Table.1 Specific gravity of sand and sawdust mixture
Sieve analysis
The results Fineness Modulus of sand and sawdust ash mixture is given in Table 2.
Paramet
er
San
d
SD
A
(S+10%S
DA)
(S+20%S
DA)
(S+30%S
DA)
(S+40%S
DA)
(S+50%S
DA)
Fineness
Modulus
2.2
1
1.7
8
2.2 2.1 2.0 1.9 1.85
Table.2 Fineness modulus of sand and sawdust mixture
3. Scanning electron microscopy of fine aggregate (Sand)
Scanning electron microscopy has distinct advantages for characterization of concrete, cement
and aggregate microstructure and in the interpretation of causes for concrete deterioration.
SEM(scanning electron microscopy) together with EDS (energy dispersive spectroscopy) is a
versatile tool which can used to image samples easily up to 50x and 500 microns magnification
and analyse fine aggregate (sand) is shown in Fig.1, Fig.2 and Table.3 .
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Fig.1 SEM (scanning electron microscopy) Fig.2 EDS (energy
dispersive spectroscopy)
of fine aggregate (sand) of fine
aggregate (sand)
Element % Weight % Atomic
Al 3.83 4.15
Si 85.51 89.09
Ca 5.70 4.16
Fe 4.97 2.6
Total 100.00
Table 3 Elements of Fine aggregate (sand)
SEM and EDS of Sawdust ash (SDA)
SEM(scanning electron microscopy) together with EDS (energy dispersive spectroscopy) is a
versatile tool which can used to image samples easily up to 5000x and 5 micron magnification
and analyse Sawdust ash (SDA) is shown in Fig.3 ,Fig.4 and Table 4.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Fig.3 SEM (scanning electron microscopy) Fig.4 EDS
(energy dispersive spectroscopy)
of Sawdust ash (SDA) of
Sawdust ash (SDA)
Element % Weight % Atomic
Mg 2.14 3.15
Al 2.08 2.76
Si 45.94 58.67
Cl 2.49 2.52
K 5.98 5.49
Ca 12.25 10.97
Fe 3.23 2.88
Cu 9.63 5.44
Zn 10.25 8.92
Total 100
Table 4 Elements of sawdust ash
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Compressive strength
The compressive strength of the concrete with sawdust ash are measured using 150mm cubes
tested at 7, 14,28 and 45 days for mix 1:1.66:3.61 at water cement ratio of 0.48.These results are
shown in Fig.5, Fig.6, Fig.7 and Fig.8.
Fig.5 compressive strength of cubes in 7 days curing. Fig.6 compressive strength of cubes in
14 days curing
Fig.5 compressive strength of cubes in 28 days curing. Fig.6 compressive strength of cubes in
45 days curing
4. Discussion of test results
Fineness modulus
With the addition of sawdust ash, the fineness modulus decreases as the ash increases. Hence, the
fine aggregate with addition with sawdust up to 15% its starts binding up together because of its
fineness and had pozzolanic effect.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Compressive strength
The compressive strength test results for the concretes containing sawdust ash fine
aggregates of cubes according to their age are very similar to each other upto 15%. Concretes
containing Sawdust ash as fine aggregates, with a mixing ratio 5%, 10%, 15% displayed an
increase in compressive strength than that of plain concrete but decreases as the % of sawdust
increases respectively.
5. Conclusion
Based on the present study the following conclusion can be drawn:
1. Sawdust ash to the extent of 15 percent replacement of sand decreases the fineness
modulus of fine aggregate making it pozzolanic.
2. The sem analysis shows the microstructure which fills up the concrete porosity.
3. The EDS show that it as high silica when helps the concrete to get solidified early.
4. There is an increase in compressive strength of concrete for the replacement by sawdust
ash upto 15%. For 15 percent replacement, the compressive strength is maximum for all 4
curing .Beyond this, the compressive strength reduces gradually. A 50% replacement, the
strength is less than normal but even that can be used in the case where less strength is
required.
REFERENCES
1. Kenai S, Benna Y, Menadi B, The effect of fines in crushed calcareous sand on properties
of mortar and concrete. In proceedings of international conference on Infrastructure
regeneration and rehabilitation a vision for next millennium, Sheffield; pp.253-61. (1999)
2. Fitzgerald O.A, He built a home of Sawdust-Concrete, In: Reprinted by the permission
from popular mechanics, copyright. (1948)
3. Paki Turgut, Cement composites with limestone dust and different grades of wood
Sawdust In: Building and Environment. (2006)
4. BMP Association Ltd. Building out of Sawdust concrete. (2008)
5. Elinwa, A.U., and Mahmood, Y.A., ―Ash from timber waste as cement replacement
material,‖ Cement and concrete Composites, V.24, No.2, pp.219-222. (2002)
6. Udocyo FF, Dashibil PU. Sawdust ash as concrete material. ASCE, 14(2):173-6. (2002)
7. Emmanuel A. Okunade., ―The Effect of Wood Ash and Sawdust Admixtures on the
Engineering Properties of a Burnt Laterite – Clay Bricks‖ Journal of Applied Sciences
8(6):1042-1048. (2008)
8. Abdullahi, M., Characteristics of Wood ash/OPC Concrete. Leonardo Elect. Practices
Technol. (LEJPT), 5(8): 9-16. (2006)
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
AN EXPERIMENTAL STUDY ON HIGH PERFORMANCE CONCRETE WITH
SILICA FUME AND FLY ASH AS PARTIAL REPLACEMENT OF CEMENT
K.R.Muthuswamy* Dr.G.S.Thirugnanam**
* Head of Department, Department of Civil Engineering, Sakthi Polytechnic College,
Sakthi Nagar- 638 315, Erode Dist.
** Head of Department, Department of Civil Engineering, Institute of Road and Transport
Technology, Erode
ABSTRACT
Concrete has been considered as a premier construction material. It is well known that
conventional concrete does not meet many functional requirements such as permeability, thermal
cracking, resistance to chemical attack, etc. Hence a new product known as High Performance
Concrete has come out with enhanced durability and long term performance.
High performance concrete can be produced by reducing water-cement ratio. Silica fume
and/or fly ash is used as a mineral admixture to make an impermeable HPC. Super plasticizer is
added to get the required workability.
In this work, mix design for M30 grade concrete has been made by IS 10262-1982
method. The HPC mixes were prepared by partial replacement of cement using different
percentage of silica fume (0, 5 & 7.5%) and fly ash (0 & 10%). Super plasticizer (dosage 0.5%
by weight of binder) was added with all mixes for workability.
The fresh concrete samples were tested for Slump, Compacting factor and VB time. The
hardened concrete samples were tested after 28 days curing for Compressive strength, Flexural
tensile strength and Split tensile strength. The results were plotted and analyzed. The optimum
percentage replacement of cement with silica fume and fly ash has been determined. The
durability of concrete has been checked by conducting Acid test, Chloride test, Rapid Chloride
Penetration Test and Corrosion test after 28 days curing. The results were analyzed and
compared with the standard requirements.
INTRODUCTION
In normal concrete, relatively low strength and elastic modulus are the result of high
heterogeneous nature of structure of material, particularly the porous and weak transition zone,
which exits in the cement paste-aggregate interface. By densification and strengthening of
transition zone, many desirable properties can be improved many fold. Reduction of w/c ratio
will greatly improve the qualities of transition zone. Silica fume and/or fly ash are used to
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
improve the qualities of transition zone. Use of appropriate super plasticizer is a key material in
making HPC.
In this paper, high performance concrete has been obtained by mixing cement, silica
fume, fly ash, fine aggregate, coarse aggregate and water in certain proportions. Super plasticizer
is added for getting workability. The performance of designed mix has been verified
experimentally.
MATERIALS USED
Cement
Ordinary Portland Cement 53 grade with specific gravity 3.15 has been used.
Silica fume
A standard quality silica fume having most particle size smaller than 1 micron, obtained
from an authorized supplier at Salem has been used.
Fly ash
Fly ash resulting from the combustion of pulverized coal in boilers and is collected
through the electrostatic precipitators at Mettur Thermal Power Plant was used in this work.
Fine aggregate
Karur river sand was used as fine aggregate. The specific gravity of sand is 2.63. The
sieve analysis indicates that the sand is conforming to grading zone III as per IS 383-1970.
Coarse aggregate
The coarse aggregate obtained from crushers in the government approved granite quarry
at T.N.Palayam, Erode was used. The specific gravity of coarse aggregate is 2.90. Sieve analysis
shows that the aggregate is conforming to graded aggregate of nominal size of 20mm as per IS
383-1970.
Water
Potable water from Bhavani river was used for this work.
Admixtures
A super plasticizer named Conplast SP-430 has been used. A dosage of 0.5% by weight
of binder was used for all the mixes.
MIX DESIGN FOR CONCRETE
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Mix design procedure recommended by IS 10262-1982 has been used. Assuming the
degree of workability as medium, degree of quality control as good and mild type exposure the
concrete mix design has been made for the M30 grade concrete. The water content is kept
constant as 0.40. The mix proportion calculated is 1 : 1.23 : 3.14. The quantities of various
ingredients per cubic meter of concrete as per the design is prepared and presented in table 1.
Sample
No.
Proportion of
binder
C:SF:FA
Weight in kg per cubic meter of concrete
Cement Silica
fume
Fly
ash
Sand Coarse
aggregate
Water
1 1:0:0 425.73 - - 522.01 1338.56 170.29
2 0.95:0.05:0 404.44 21.29 - 522.01 1338.56 170.29
3 0.925:0.075:0 393.80 31.93 - 522.01 1338.56 170.29
4 0.85:0.05:0.10 361.87 21.29 42.57 522.01 1338.56 170.29
5 0.825:0.075:0.10 351.23 31.93 42.57 522.01 1338.56 170.29
Table 1. Quantities of ingredients per cu.m. of M30 concrete
EXPERIMENTAL INVESTIGATIONS
In this work, the workability of fresh concrete has been determined by conducting the
Slump test, Compacting factor test and VB time test. The strength of hardened concrete has been
determined by conducting Compression test on cubes, Flexural strength on beams and Split
tension test on cylinders after 28 days. The durability of concrete has been determined after 28
days by conducting Acid test, Chloride test and Rapid Chloride Penetration test. The results are
presented in the following articles.
Workability of fresh concrete
Sample No. Slump in mm Compacting factor VB time in seconds
1 21 0.90 10
2 40 0.91 9
3 64 0.93 7
4 90 0.90 8
5 78 0.88 11
Table 2. Workability test results
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Strength of hardened concrete
Sample No. Comp. strength on cubes
N/mm2
Flexural tension
N/mm2
Split tension
N/mm2
1 35.12 4.45 4.18
2 38.89 4.9 5.13
3 42.22 5.06 5.66
4 39.46 4.99 4.67
5 30.67 4.63 4.32
Table 3. Strength of Concrete test results
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Durability of concrete
From the workability and strength test results it is concluded that the optimum
replacement of cement by silica fume is 7.5% (without fly ash). Hence durability tests were
conducted only for the specimens cast by using cement replaced by 7.5% silica fume only.
Acid test
The cube (150mm x 150mm x 150mm) specimens were used after 28 days curing. The
cubes were immersed in 1% by weight of Sulphuric acid for 30 days. The loss of weight and
compressive strength were determined.
Concret
e grade
Weight of cube in kg Compressive strength in N/mm2
Before
immersi
on
After
immersi
on
Loss
of
weight
% loss
of
weight
Before
immersi
on
After
immersi
on
Loss
of
weight
% loss of
weight
M30 8.588 8.360 0.028 0.33 12.58 10.50 2.08 16.53
Table 4. Acid test report after 30 days
Chloride test
The concrete cubes (150mm x 150mm x 150mm) cured for 28 days were immersed in
3% by weight of sodium chloride for 30 days. The gain in weight of cube and loss of
compressive strength were measured.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Concret
e grade
Weight of cube in kg Compressive strength in N/mm2
Before
immersi
on
After
immersi
on
Gain
of
weight
% gain
of
weight
Before
immersi
on
After
immersi
on
Loss
of
weight
% loss of
weight
M30 8.32 8.464 0.04 0.47 12.35 8.5 3.85 31.17
Table 5. Chloride test report after 30 days
Rapid chloride penetration test
The concrete specimens for test were made in the form of slices 51mm thick and 102mm
nominal diameter cylindrical specimen. The RCPT apparatus consists of two reservoirs. The
specimen was fixed between the two reservoirs using an epoxy bonding agent to make the test
set-up leak proof. One reservoir (connected to the positive terminal of the DC source) was filled
with 0.3N sodium hydroxide solution and the other reservoir connected to the negative terminal
of the DC source with 3% sodium chloride solution. A DC of 60v was supplied across the
specimen using two stainless steel electrodes and the current across the specimen was recorded at
30minutes interval for the duration of 6 hours. The total charge passed during this period was
calculated in terms of coulombs using the trapezoidal rule is given by the equation,
Q = 900 (I0+2I30+2I60+…………….+2I330+2I360)
Where Q = Charge passed (coulombs)
I0 = Current (amperes) immediately after the voltage is supplied and
It = Current (amperes) at t minutes after the voltage is supplied
Specimen Weight in kg % gain in
weight
Before RCP After RCP Increase in
weight
M30 concrete
slice
1.062 1.096 34g 3.2
Table 6. Gain in weight due to chloride penetration
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
Measurement of chloride ion penetrability
Period of
measureme
nt in mm
0 30 6
0
90 120 15
0
18
0
21
0
24
0
27
0
30
0
33
0
36
0
Current in
amperes
0.1
20
0.1
26
0.1
30
0.1
34
0.1
40
0.1
44
0.1
48
0.1
50
0.1
52
0.1
56
0.1
58
0.1
64
0.1
64
Table 7. Current penetrability characteristics
The total charge passed, Q = 3287 coulombs
DISCUSSION OF RESULTS
Workability of fresh concretes
From the experimental observations, it is to be noted that the slump value is getting
increased with increase in silica fume content. The maximum slump is obtained for 5% silica
fume and 10% fly ash in cement. The slump gets decreased with addition of fly ash along with
silica fume and cement. The optimum percentage replacement of cement is 5% silica fume and
10% fly ash.
The compaction factor values increase up to 7.5% replacement of cement by silica fume.
It is maximum for 7.5% replacement of cement with silica fume. With the addition of fly ash in
cement, the compaction factor gets reduced.
The VB time observation shows that the VB time is minimum at 7.5% replacement of
cement with silica fume and hence the workability is good with 7.5% silica fumes in cement.
Strength of hardened concrete
The compressive strength results reveal that the compressive strength of concrete
increases with increase in silica fumes content in cement. The compressive strength is maximum
at 7.5% replacement of cement with silica fume. The compressive strength of samples 4 and 5
gets reduced because of increased powder content due to the addition of fly ash along with silica
fume and cement.
The flexural tensile strength or modulus of rupture is also getting increased with increase
in replacement of cement with silica fume up to 7.5%. Further the flexural strength gets reduced
with the addition of fly ash along with silica fume and cement.
The split tensile strength results indicate that the strength is increasing up to 7.5%
replacement of cement with silica fume. The results get reduced for samples 4 and 5 because of
fly ash as in other strengths.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
In general all the strengths explained above were optimum at 7.5% replacement of
cement with silica fume. The silica fume up to 7.5% acts as a pore filler for getting dense
compact concrete. It also reacts with calcium carbonate in concrete and creates more C-S-H gel
and improving the qualities of transition zone. Hence the strength is increasing very well.
The addition of fly ash along with silica fume to replace cement content, increase the
volume of fine powder content in excess of that required for pore filling and to produce the gel.
Hence the strength is getting reduced.
Durability of concrete
Acid and chloride penetration results indicate that the loss or gain in weight is very less.
Hence the concrete is impermeable against the penetration and promises long term durability.
Rapid chloride penetration test result shows that the chloride ion penetrability is moderate
as per ASTM C1202. Hence the quality of concrete is moderate. The value of current is
increased with time due to the penetration of chloride ion. Chloride ion reduces the resistance of
concrete.
CONCLUSIONS
The following conclusions were drawn from this work,
1. The workability of concrete is good with the addition of silica fume up to 7.5% and fly
ash up to 10% along with silica fume as partial replacement of cement.
2. The optimum percentage of silica fume in cement is 7.5% to get maximum workability of
concrete
3. The strength of concrete (compression, flexural tension and split tension) is increasing
with increase in silica fume content (up to 7.5%) in cement. The strength gets reduced
with the addition of fly ash along with silica fume in cement because of more filler
material.
4. The optimum strength is achieved with 7.5% replacement of cement with silica fume.
5. The durability of concrete is good from the results of acid test and chloride test. The
weight loss/gain and strength loss are very less in acid/chloride penetration.
6. The chloride penetrability is moderate in rapid chloride penetration test. Hence the
quality of concrete is moderate.
In general, the concrete with silica fume content of 7.5% as partial replacement of cement
performs very well with respect to workability, strength and durability characteristics. Hence
the concrete designed can be considered as a high performance concrete.
Proceedings of the National Conference on “Recent Advances in Concrete, Steel and Composites Structures”, IRTT, Erode on 27th Aug, 2009.
REFERENCES
1. Dr. Perumal, research study on ―Development of High Performance Concrete using
silica fume as partial replacement of cement‖, 2007
2. Gopalakrishnan.S, N.P.Ragamane, M.Neelamegam, J.A.Peter and
J.K.Dattatraya ―Effect of partial replacement of cement with fly ash on the strength
and durability of HPC‖ Indian Concrete Journal, May 2001, pp335-341
3. Shetty M.S., ―Concrete Technology‖ S.Chand & Company ltd., New Delhi, 2005
4. Santhakumar A.R., ―Concrete Technology‖, Oxford press, New Delhi, 2005
5. IS 383-1970, ―Specification for coarse and fine aggregate from natural sources of
concrete‖, BIS, New Delhi.
6. IS 10262-1982, ―Recommended guidelines for concrete mix design‖, BIS, New
Delhi.
7. IS 456-2000, ―code of practice for plain and reinforced concrete‖, BIS, New Delhi.