national conference on “recent advances in concrete, steel and composites structures”,...

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


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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

[email protected]

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

mailto:[email protected]


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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


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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.


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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


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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.


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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


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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)


13

]

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%


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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.


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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


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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

http://en.wikipedia.org/wiki/Buckling

http://en.wikipedia.org/wiki/Buckling


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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.


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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


19

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.


20

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


21

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.


22

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.


23

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


24

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


25

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.


26

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


27

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


28

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.


29

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.


30

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.


31

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


32

(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


33

(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.


34

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.


35

(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:


36

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.


37

* 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.


38

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.


39

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


40

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


41

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


42

Fig.4 Carbonation Process


43

Fig.6 Chloride Induced Macro Cell Corrosion of Steel in Concrete


44

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


45

RE O

TR

L1

L2

L3

L1 L2 L3 O

INPUT OUTPUT

TR

RE crack

TR

RE


46

Fig.9 Ultra-Sonic Test

1 2 1 2 3

Oscillosco

pe

Screen

Uncracked

Specimen

Cracked

Specimen

(a)

(A)


47

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


48

Fig.11 Half-Cell Potential

Fig.12 Cathodic Protection

Current Source

Pipe being

protected

Sacrificial anode

Conducting back fill


49

STEP-1 STEP-2

STEP-4 STEP-5

STEP-7 STEPS 3 TO 5 SAME AS BEFORE

Ld Ld


50

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.)


51

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


52

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


53

(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.


54

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


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.


71

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


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


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


76

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:


77

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.


78

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.


79

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.


80

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

)


81

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


82

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


83

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


84

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)


85

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.


86

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.


87

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].


88

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.


89

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.


90

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.


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


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


93

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


94

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


95

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


96

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%


97

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


98

Fig.8 Flexural Test Specimen (Reference)

Fig. 9 Flexural Test Specimen - Polyolefin Fibre (0.5%-2%)


99

Fig. 10 Flexural Test Specimen- Steel Fibre (0.5%-2%)


100

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.


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.




101

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%


102

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


103

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.


104

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 -


105

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


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.


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


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


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.


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.




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.


Specific gravity

The results specific gravity of sand and sawdust ash mixture is given in Table 1.


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 .


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)


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


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


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


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



115

Fig.5 compressive strength of cubes in 28 days curing.



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.


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)


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)


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] &

2 [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.



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.


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


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


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


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


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


Fig. 6.b- Load-Deflection Diagram-Right side

Fig 6. a -Load- Deflection Diagram-Left side


Fig 7 Variation of Ductility Factor with Forward Load Cycles-Left Side

Fig 8 Variation of Ductility Factor with Backward Load Cycles-Left Side


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


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


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


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


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


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


Fig 21 Variation of Stiffness with Load Cycles – Forward Cycles-Left side

Fig 22 Variation of Stiffness with Load Cycles –Backward Cycles-Left side


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.


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.


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.


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


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 #


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


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.


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)


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:


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 %


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


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


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


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:


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.


PROPERTIES OF BRICKS WITH PARTIAL REPLACEMENT OF

BRICK EARTH BY STEEL SLAG

P.S.Kothai

Senior Lecturer, Kongu Engineering College,Perundurai,Erode

[email protected]

Dr.R.Malathy

Principal, Excel Engineering College, Komarapalayam

[email protected]

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


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.

http://www.answers.com/topic/mortar

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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.

http://www.answers.com/topic/extrude

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http://www.answers.com/topic/kaolin

http://www.answers.com/topic/shale

http://www.answers.com/topic/manganese

http://www.answers.com/topic/barium-carbonate

http://www.answers.com/topic/ammonium

http://www.answers.com/topic/disperse

http://www.answers.com/topic/nepheline-syenite

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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 (%)


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%.


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


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


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


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)


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


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


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


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 &


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.


STUDY ON FLY ASH BASED GEO-POLYMER CONCRETE.

Ms.C.Chella Gifta,

Lecturer

Department of Civil Engineering.

St.Peter’s Engineering College, Chennai 54.

[email protected]

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.



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


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.


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


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


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


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


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


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


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 %.


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

%.



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


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


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


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.


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.


DESIGN OF COLD-FORMED STEEL PLAIN CHANNELS

S.Manjuladevi1

1Lecturer, Department of Civil Engineering

Sathyabama University, Chennai

[email protected]

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.


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


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


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


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


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.


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


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


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


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


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).


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.


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.


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.


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 .


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.


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.


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


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.


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


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.



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.


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.


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


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


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


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.


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.


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


Specific gravity 2.80

Fineness modulus 5.96

Size Passing through 20mm sieve and

retained in 10mm sieve


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


(MPa)

a) 3 days 28 23

b) 7 days 38 33

c) 28 days 44 43


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.


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


Cube and Cylinder Specimen Fig .3 Specimens after curing

Fig. 4 Reinforcement detailing of Flexure Beam

Fig .5 Reinforcement Detailing of Shear Beam


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


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


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


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.


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.


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.


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


Fig: 5 Base Isolation in Buildings


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.


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.


Fig 7: Seismic Energy Dissipation Devices – each device is suitable for a certain building.


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.


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


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


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


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


REINFORCEMENT DETAILS OF NORMAL BEAM

All dimensions are in mm


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:


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.


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


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.


carries 8.1% more load for bottom portion wrapped condition.


carries 26.15% more load for middle third portion wrapped condition.



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.


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


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


FIGURE 1 GLASS FIBER MAT

FIGURE 2 WELD MESH


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


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


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)


Beam(FS2)


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


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


Beam(FS1)


Beam(FS2)


Beam(FS3)

Weld Mesh

Strengthened

Beam(FSWM)


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.


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


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.


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.


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


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


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


(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


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.


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.


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


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.


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


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.


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.


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


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


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


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


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


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.


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.


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.


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


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.


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


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.


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.


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.


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


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




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.


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.


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 .


Fig.1 SEM (scanning electron microscopy) Fig.2 EDS (energy

dispersive spectroscopy)

of fine aggregate (sand) of fine

aggregate (sand)


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)


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.


Fig.3 SEM (scanning electron microscopy) Fig.4 EDS

(energy dispersive spectroscopy)

of Sawdust ash (SDA) of

Sawdust ash (SDA)


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



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.



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)


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


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


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


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


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.


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


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.


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.


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.

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