effect management of elevated temperature on mechanical and microstructure properties of reinforced...

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),

ISSN 0976 – 6316(Online), Volume 5, Issue 11, November (2014), pp. 165-180 © IAEME

165

EFFECT MANAGEMENT OF ELEVATED

TEMPERATURE ON MECHANICAL AND

MICROSTRUCTURE PROPERTIES OF REINFORCED

CARBON FIBER LIGHTWEIGHT CONCRETE

Dr. Alya’a Abbas AL-Attar1, Dr. AmmarSaleem Khazaal

2, Dr. FirasKhairy Jaber

3

1(Lecture, Technical College of Kirkuk, Iraq)

2(Lecture, Dept.of Civil Engineering, TikritUniversity, Iraq)

3(Lecture, College of Electrical and Electronic Engineering Techniques, Baghdad, Iraq)

ABSTRACT

This paper studies the effect management of high temperature on mechanical characteristics

of carbon fiber reinforced light weight aggregate concrete. The effect of using high range water

reducing agent HRWRA (High range water reducing admixture) with 8% SF (silica fume), as a

partial replacement by weight of cement, on the behavior of LWAC (Light weight aggregate

concrete) is also studied. Workability, fresh and hardened density, compressive strength, splitting

tensile strength and modulus of rupture tests were performed, on specimens of both ages 7 and 28

days. The test results indicated that the inclusion of carbon fiber to the light weight concrete mix did

not affect the compressive strength significantly, while the splitting tensile strength and the modulus

of rupture were improved significantly. The addition of silica fume improves the compressive,

splitting tensile, and modulus of rupture strengths of carbon fiber light weight concrete. The average

improvement was about (26.5%, 71% and 73 %) respectively for carbon fiber LWAC containing

silica fume. Microstructural properties were studied at ambient temperature and after heating. For

each test, the specimens were heated at a rate of 1 C°/min up to different temperatures (150, 450,

600, and 1000°C). In order to ensure a uniform temperature throughout the specimen, the

temperature was held constant at the target temperature for one hour before cooling. In addition, the

specimen mass was measured before and after heating in order to determine the loss of water during

the test. The results allowed us to analyze the degradation of LWAC due to heating. Between 20 and

150 °C, it was associated to an evaporation of free water as well as to an increase in porosity of the

tested concretes. Between 150 and 600 °C, in a similar way to the observed evolutions between 20

and 150 °C, due to the departure of bound water, corresponding to a large mass loss. The

improvement in microstructure could be attributed to a modification of the bonding properties of the

cement paste hydrates (rehydration of the paste due to the migration of water in the pores). Beyond

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600 °C, the microstructure of the tested concretes deteriorated quickly. The specimens subjected to a

heating up to 1000 °C showed very weak physical properties (appearance of microcracking).

Keywords: Light Weight Aggregate Concrete, Management Microstructure, Elevated Temperature.

1- INTRODUCTION

The demand for structural lightweight concrete in many applications of modern construction

is increasing, owing to the advantage that lower density results in a significant benefit in terms of

load-bearing elements of smaller cross sections and a corresponding reduction in the size of the

foundation. Structural lightweight concrete has its obvious advantages of high strength/weight ratio,

good tensile strain capacity, and low coefficient of thermal expansion due to the voids present in the

lightweight aggregates. lightweight concrete has successfully been used for many years for

structural members and system in buildings weight, which permits saving in dead loads, and thus

reducing the costs of both superstructure and foundation, it is more resistance to fire and provides

better heat and sound insulation than concrete of normal density.The lightweight concrete have

densities from 1000 to 2000 kg/m3 and compressive strengths from 1 to 100 Mpa. They can be made

light by adding lightweight aggregate such as plasticizers to cement, with fiber reinforcement to

decrease their density while keeping their mechanical strength.

In view of global sustainable development, it is imperative that supplementary cementing

materials be used in place of cement currently used in the concrete industry. The most available

supplementary cementing materials worldwide are silica fume (SF), a byproduct of silicon, and fly

ash (FA), a byproduct of thermal power stations. As environment pollution become problem, the idea

of using the west materials has gained popularity. In literature, the researchers have indicated that

addition of SF highly dense the structure of concrete, which could result in an explosive swelling due

to a build-up of pore pressure by steam. Since the evaporation of physically absorbed water starts at

80C°, which induces thermal cracks, such concretes may show performance inferior to the pure

concretes at elevated temperatures.

2- LITERATURE REVIEW

Dhir et al.(1), studied the mix design and properties of all lightweight concrete made from

Aglite aggregate. Eight mixes were prepared with cement content that varied from (250 to 600)

kg/m3. The water content for all mixes was 300 kg/m

3. Pulverized fuel ash (PFA) was used as a

partial replacement by weight of cement. Water reducing admixture also was used in different

dosages. They studied compressive strength, tensile strength, drying shrinkage and modulus of

elasticity. The concrete containing (PFA) and water reducing admixture are capable to achieve 28

days compressive strength in the range of (25 to 50) MPa with densities between (1525 to 1703)

kg/m3.

Al-Haddad (2), investigated the durability of porcelinite lightweight aggregate concrete

containing high range water reducing agent and slag against sulfates and chlorides solution. Nine

mixes were used with cement content that varied in the range (400 to 600) kg/m3. The author studied

the effect of using high range water reducing agent and high reducing agent with 10% slag as a

partial replacement by weight of cement, on the durability of (LWAC). From this investigation he

pointed out that it is possible to produce (SLWC) of 28 days compressive strength in the range (21.5

to 37.5) MPa with an air dry density between (1845 to 1965) kg/m3.

A1-Timimy(3), investigated the properties of glass fiber reinforced concrete using metakaolin

material with (10, 30 and 50) % as a partial replacement by weight of cement. The micro structural

characteristics obtained by the scanning electron microscopy are in agreement with results obtained



167

by the x-ray diffraction examination. These tests clearly indicated that the metakaolin concrete

specimens have higher proportion of (C-S-H) and less amount of calcium hydroxide compared to

concrete mixes without metakaolin. The test results showed that the mechanical properties of

metakaolin composite are enhanced significantly as compared with reference and fiber reinforced

concrete. Results also showed that the inclusion of the metakaolin into fiber reinforced specimens

shows a significant reduction in the porosity and absorption as compared to reference and fiber

reinforced concrete without metakaolin.

Zeng and Chung(4), investigated the influences of chemical agents on the improvement of

carbon fiber reinforced cement composite by using short pitch-based carbon fibers 0.5% by weight

of cement, together with a water reducing agent and accelerating admixture. Results indicated that

compressive, tensile and flexural strength of the carbon fiber reinforced cement mortar were found to

increase by about (18 to 31) %, (113 to 164) % and (89 to 112) % respectively, compared to the

corresponding plain cement values.

3- OBJECTIVE OF RESEARCH

The research aims to study the significance of using LWAC in structural approach by

improving the performance using mineral & chemical admixtures and fibers as well, and also to

study the effect of exposure to fire, so that it states to which temperature the LWAC can sustain.

4- EXPERIMENTAL PROGRAM

To produce structural light weight aggregate concrete, crushed porcelinite stone was used as a

coarse light weight aggregate and natural sand as a fine aggregate. Chemical and mineral admixtures

as well fibers were also used to enhance performance of light weight concrete.

4. 1) Materials

4. 1.1) Cement

Ordinary Portland cement (Type I) was used in all mixes throughout this investigation. It was

stored in air – tight plastic containers to avoid exposure to atmospheric conditions. The percentage

oxide composition indicated that the adopted cement conforms to the Iraqi specification No.

5/1984.). The Chemical composition and main compounds of cement used in this investigation show

in table (1) and The chemical and physical properties of this cement are presented in Tables (2) .

Table (1): Chemical composition and main compounds of cement used in this investigation Oxides composition Content % Limit of Iraqi specification No. 5/1984

Line, CaO 62.5 % - Silica, SiO2 21.4 % -

Alumina, Al2O3 4.6 % - Iron oxide, Fe2O3 3.3 % Magnesia, MgO 3.0 % 5 % Max.

Sulfate, SO3 2.6 % 3 % Max. Loss on Ignition, (L.O.I) 1.0 % 4 % Max.

Insoluble material 1.3 % 1.5 % Max. Lim Saturation Factor, (L.S.F) 0.9 (0.66-1.02)

Main Compounds (Bogues equation) C3S 48.7 % C2S 24.8 % C3A 6.6 % > 5 %

C4AF 10 %



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Table (2): Physical properties of cement used in this investigation* Physical Properties Test Results Limit of Iraqi specification No. 5/1984

Specific surface area (Blaine method), (m2/kg) 311 230 m

2/kg lower limit

Setting time (vacate apparatus) Initial setting, hrs : min Final setting, hrs : min

2:40 3:50

Not less than 45 min Not more than 10 hrs

Compressive strength MPa For 3-day For 7-day

20.4 30.2

15 MPa lower limit 23 MPa lower limit

Expansion by Autoclave method 0.38 % 0.8 % upper limit

4.1.2) Fine aggregate

Normal weight natural sand from AL-Tuz region was used as fine aggregate. The grading of

the sand conformed to the requirement of Iraqi specification No. 45/1984, zone (3). Table (3) shown

Grading of fine aggregate and The Physical and chemical tests on sand used throughout this work are

shown in Table (4).

Table (3): Grading of fine aggregate

Sieve size Cumulative passing % Limit of Iraqi specification No. 45/1984

4.75 100 90-100

2.36 89.32 85-100

1.18 82.56 75-100

0.6 64.81 60-79

0.3 20.9 12-40

0.15 3.22 0-10

Table (4): Chemical and physical properties of the sand.

4.1.3) Coarse aggregate

Local naturally occurring light weight aggregate of porcelinite stones was used as coarse

aggregate. It was brought in large lumps from the State Company of Geological Survey. The lumps

were firstly crushed into smaller sizes manually by means of a hammer in order to facilitate the

insertion of lumps through the feeding openings of the crusher machine. The crushed aggregate is

grouped to different sizes and then the required coarse aggregate was prepared to conform to ASTM

C192M-02 (5) specification. Table (5) shows the grading of the used coarse light weight aggregate.

Table (6) shows the results of tests of chemical and mineral analysis of porcelinite aggregate and the

table (7) and Table ( 8) show the Chemical analysis of porcelinite aggregate and Mineral analysis of

porcelinite aggregate respectively.

Properties Specification Test Results Limits of specification

Specific gravity ASTM C128-01

2.60

Absorption % ASTM C128-01

2.2

Dry loose unit weight, kg/m3 ASTM C29/C29M/97

1590

Sulfate content (as SO3), % (I.O.S.) No. 45-84 0.08 0.5 (max. value)

Material finer than 0.075 mm sieve, % (I.O.S.) No. 45-84 1.18 5 (max. value)



169

Table (5): Selected grading of coarse lightweight aggregate

Sieve size (mm) Cumulative passing (%) Cumulative passing %ASTM C330

12.5 100 100

9.5 92.02 80-100

4.75 23.76 5-40

2.36 5.38 0-20

1.18 0 0-10

Table (6): Chemical and physical properties of porcelinite lightweight aggregate

Properties Specification Test Results

Specific gravity ASTM C127-01

1.52

Absorption % ASTM C127-01

35

Dry loose unit weight, kg/m3 ASTM 29/C29M/97

775*

Dry rodded unit weight, kg/m3 ASTM 29/C29M/97

820

Aggregate Crushing value % BS 812-part 110-1990

16

Sulfate content (as SO3), % BS 3797-part 2-1981 0.32

Staining Materials:***

Stain intensity

Stain index ASTM 641-98

No stain

0

Table (7): Chemical analysis of porcelinite aggregate

Oxides % by Weight

SiO2 69.86

CaO 10.57

MgO 6.90

SO3 0.30

Al2O3 4.78

Fe2O3 2.09

TiO2 0.18

L.O.I 4.25

Total 98.97

Table (8): Mineral analysis of porcelinite aggregate*

Compounds % by Weight

Opal-C+ 63.82

Quartz 9.62

Dolomite 7.20

Gypsum 7.05

Halite 0.71

Apatite 0.74

Clay 9.77

4.1.4) Super plasticizer (SP) A super plasticizer type (GLENIUM51) based on modified polycarboxylic either was used

throughout this investigation. (It is free from chlorides and complies with ASTM C494M/04 types A

and F. Table (9) indicates the technical description of the aqueous solution of super plasticizer used

throughout this investigation.



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Table (9): Technical description of high range water reducing admixture

Main Action Concrete Superplasticizer

Form Viscous Liquid

Colour Light Brown

Relative Density 1.1 g/cm3 @ 20

°C 6.6

pH value 6.6

Viscosity 128 1.30 cps @ 20 °

C

Transport No + classified as dangerous

Labeling No hazard label required

4.1.5) Silica Fume Silica fume was used in this investigation Elkem micro silica produced by Efaco/Egypt. The

chemical oxide composition of the silica fume is given in Table (10). The physical properties are

given in Table (11).

Table (10): Chemical analysis of silica fume

Oxides Composition Oxide Content %

SiO2 94

Al2O3 2.03

Fe2O3 1.32

CaO Nil

MgO 2.00

K2O Nil

Na2O Nil

Total 99.35

Table (11): Physical and chemical properties of SF used

Physical Properties Silica Fume (SF)

Unit weight kg/m3 2.45 kg/m

3

Specific Gravity 2.32

The amount of Silica Fume remaining on a 45 µm sieve 4.8 %

4.1.6) Carbon fiber

High performance high strength carbon fiber system for structural reinforcement was used in

this investigation. It has a high impact resistance, very good tensile strength and elastic modules.

Also it has a very good chemical resistance under variety of exposure condition. Table (12) shows

the general properties of the used carbon fiber.

Table (12): Physical properties of carbon fiber used in this investigation.

Grade 300 HS

Weight (g/m³) 300.00

Design thickness (mm) 0.17

Tensile strength design (kgf/ cm²) 35.50

Fiber length (mm) 19.00

Carbon content (%) 98 wt

Specific gravity 1.90

Elongation at break (%) 1.40



171

4.2) Concrete mixes Concrete mixes containing porcelinite aggregate as light weight aggregate should have an

oven-dry density < 2000 kg/m³ and a compressive strength > 15 MPa to produce structural (LWAC).

These mixes were designed in accordance with ACI commitlee 211-2-81. In general, this

experiments design was applied to investigate the effect of SF, carbon fiber and temperature on the

compressive, tensile and flexural strength of porcelinite light weight concrete. The details of these

mixes are given in Table (13), and Table (14) lists the variables and levels used in the experimental.

Table (13): Details of the mixes used throughout study

Designation

of mixture

Cement

content

Kg/m3

Silica fume

Kg/m3

Carbon

fiber % by

volume

Coarse

lightweight

aggregate kg/m3

HRW Superplastizer

% by weight of

cement

1 550 - 0 518 5.5

2 550 - 0.5 518 5.5

3 550 - 1.25 518 5.5

4 550 - 2.5 518 5.5

5 495 55 0 518 5.5

6 495 55 0.5 518 5.5

7 495 55 1.25 518 5.5

8 495 55 2.5 518 5.5

Table (14): Variables used in these experiments

variables 1 2 3 4

Temperature 150 450 600 1000

Silica fume 0 10 - -

Carbon fiber 0 0.5 1.25 2.5

4.3) Preparation, casting and curing of specimens

Steel moulds were used for casting all specimens. They were cleaned and oiled before

casting. The fresh concrete was placed inside the molds with approximately equal layers of 50 mm

and compacted by means of vibrating table. Care has taken to avoid segregation of mixes. After the

top layer had been compacted, it has smoothed, then the mould covered with nylon sheets for 24

hours to reduce evaporation of water to avoid plastic shrinkage cracks. After 24 hours the specimens

were de-molded and completely immersed in tap water until the time of testing. Demoulding was 24

h after casting and placed in a water tank at 25±2 C°. After 28 days water curing, they heated in an

electric furnace up to 150, 450, 600, and 1000 °C.

The heating rate was set at 1 C°/min as used in previous research. Each temperature was

maintained for 1 h to achieve the thermal steady state. The specimens were allowed to cool naturally

to room temperature. Cubic specimens of dimension (100 x 100 x 100) mm, were prepared to

determine the effect of temperature on compressive strength. Cylinder specimens of dimension

(150 x 300) mm were prepared to determine the effect of temperature on tensile strength. Beam

specimens of dimensions (100 x 100 x 500) mm were prepared to determine the effect of

temperature on flexural strength.

A slice from fracture surface specimen to be examined, is cut to a suitable thickness of (3-5)

mm, and oriented in any required manner to make a polished section for examination by this

technique. Most samples to be analyzed required vacuum drying and then a conductive coating with

ultra-thin gold coating. Plate (3) reveals the type of Scanning Electronic Microscope (SEM)

equipment used for the analysis of the specimens in this study.



172

Plate (3): Scanning Electronic Microscope apparatus (SEM)

4.4) Exposure to Elevated Temperature

In order to study the effect of exposure to elevated temperatures on samples, exposure to

temperature which were 150, 400, 600, and 1000°C, 12 samples of (Cubes, Cylinders, and Prisms)

for each age, as indicated above were taken. The data after exposure to the temperature rates

mentioned above were compared with their related samples not exposed to temperature. An electrical

oven was used for heating samples in a range of 1C° per minute up to reach the target temperature as

shown in figure (1) in below.

Plate (1) Specimens layout at furnace

Fig. (1): Heating and cooling curves

5- EVALUATION OF MECHANICAL PROPERTIES

5.1 Compressive Strength

The compressive strength test was determined according to B.S. 1881: part 116: 1989. This

test was conducted on (150 x 150 x 150) mm cubes using an electrical testing machine with a

capacity of 2000 kN at loading rate of 0.25kN per second. The average of three concrete cubes has

adopted for each test, the test has conducted at ages of (7, 28, 60, 90, and 180) days for samples not

exposed to high temperature and (7, 28, 60, 90, and 180) days for samples that were exposed to

elevated temperature.

5.2 Flexural Toughness

Flexural toughness test has carried out on (100×100×500) mm simply supported prisms with

a clear span of 450 mm under the third points loading according to ASTM C1018-97, 2004. This test

has conducted at ages of (7, 28, 60, 90, and 180) days for samples not exposed to high temperature

and (7, 28, 60, 90, and 180) days for samples were exposed to high temperature. The specimens were



173

tested using a Universal Machine. To facilitate deflection reading despite the fact that the test was

performed upside down without harming the dial gauge.

The load has applied by using hydraulic machine with capacity of 2000 kN. The mid span

deflection reading has measured using a dial gauge sensitive to 0.01mm then the load deflection has

drawn according to (ASTM C1018-97, 2004) as shown in Fig. (2).

Fig. (2): Load-Deflection curve (ASTM C1018-97, 2004)

6- EVALUATION OF MICROSTRUCTURE PROPERTIES

The (SEM) photographs results at an age of 60 days of curing revealed the typical cases of

dense cement gel crystal of readily distributed shape in addition to uniform crystals from (C-H)

layers as shown in Plate (4). Continuous with curing for age of 90 days the cement gel developed to

dendritic fibers like shape was identified as shown in Plate (5).

Plate (4): Micrograph of LWAC Plate (5) Micrograph of LWAC

at age of 60 days at age of 90 days

Plate (6): Micrograph of LWAC at 150 °C Plate (7): Micrograph of LWAC at 450 °C



174

Plate (8): Micrograph of LWAC at 600 °C Plate (9): Micrograph of LWAC at 1000 °C

6.1 Exposure to temperature rate of 150 °C

It is noted that at this temperature the re-cracks in the C-H layer began as shown in Plate (6),

it can be seen more clearly where C-H layer turned to irregular shape with a clear segregation in

layers of C-H and longitudinal grooves were present. This means start of deterioration in

microstructure.

6.2 Exposure to temperature rate of 450 °C:

It is clearly that the microstructure seems good and developed to be semi homogenous so that

C-H and C-S-H layers can be thoroughly distinguished, it can be concluded that a re-hydration was

happened and leads to improvement in microstructure. It has noted also an entanglement in Needle

like shape in dark areas (pores) and that means a re-combination is going forward to seal pores (or

slots) in microstructure as has shown in plate (7).


It seems that the microstructure gets instability and turned to be like reefs with distinguished

separation in C-H layer and dark spots, X-Mas tree like shape, and cluster like shape. All the above

like shapes are indications (or signs) to weakness in bond forces between particles of microstructure

as shown in plate (8).


Significant deterioration in microstructure at this rate of temperature exposure and turned to

be like mountains, valleys with more fragmentation in both C-H and C-S-H layers of distinguished

heads and dark spots, also it is noted that both layers were arranged in vertical manner with part of

them existing in horizontal planes which means a great destabilization in microstructure as shown in

plate (9).

7- RESULTS AND DISCUSSION

7.1) Compressive Strength

The compressive strength development at various curing ages for selected mixes Reference

mix (R) and Hybrid mix (H) is presented in Table (15). Test results are illustrated that in general; R

and H specimens exhibited continuous development in strength up to 90 days of curing. There is a

considerable increase in compressive strength of (H) mix relative to its similar (R) mix without

fibers. The percentages of increase are shown in Table (15). This behavior was due to a reduction in

w/cm (water cementitious material ratio) as well as to the deflocculating or dispersion of cement

agglomerates into individual particles; thereby a greater rate of cement hydration can be achieved in

the well dispersion system according to Mehta, P. K., (1986).The development of compressive

strength versus curing age for both R and H mixes are shown in Table (15) and Fig. (3).



175

Table (15): Compressive Strength Results of R6 and H6 Mixes

Age,

(Days)

Compressive

Strength of (R)

Mix,(MPa)

Compressive Strength

of (H) Mix,(MPa)

Increase in Compressive

Strength%

7 22 30 36.36

28 28.59 38 32.91

60 37.78 49 29.70

90 43.85 51 16.31

180 51.64 53 2.63

Fig. (3): Compressive strength versus curing age of (R) and (H) mixes

7.2) Elevated Temperature Effects

The Specimens were subjected to four degree of temperature cycles up to 150, 450, 600, and

1000 C°. The first part of each cycle consisted of heating at 1 C°/min up to the target temperature.

After that, the temperature was held constant for 1 h(hour) in order to ensure uniform temperature

throughout the specimens, the last part of the cycles consisted of cooling down to ambient

temperature as shown in Fig. (1), the rate of heating refers to the recommendations of the RILEM

Technical Committee 129-MHT, 1995.

The properties measured after heating and cooling were compared to initial properties. Table

(16) shows the dispersions obtained for the compressive strength of both R and H mixes. Values of

H mix are slightly higher than those of R mix due to homogeneity and reproducibility. During the

test, spalling was observed for both mixes during the heating up to 600 C°; spalling occurred around

515 C° and this observation agrees with M. Kanema, (2007). The two mixes (R) and (H) specimens

possessed an initial compressive strength equal to 22 and 30 MPa, respectively. The variation of

residual compressive strength versus temperature is well illustrated in Table (16) and Figs. (4) and

(5). An important increase in compressive strength of about 11.22 % between 150 and 450 C° for (R)

mix specimens at an age of 60 Days, and 6.22 % for H6 mix specimens for the same age were noted;

while at an age of 90 days R6 mix specimens showed an increase of about 3.2% compared to 3.53%

for (H) mix specimens. Several hypotheses were proposed in the literature to explain this increase; it

attributes to re-hydration of the paste due to migration of water in the pores. Another study assumed

that the Silanol groups lost a part of their bonds with water which induced the creation of shorter and

stronger Siloxane elements (Si-O-Si) with probably larger surface energies that contributed to the

increase in strength according to Khoury, (1992) and Xu et al., (2001).

Beyond the 450 C°, the mechanical properties of the tested (R) and (H) mixes specimens

decreased rapidly. The specimens subjected to a heating up to 1000 C° showed very weak

mechanical properties associated with that of physical properties (Appearance of Cracking).It was

noted that for (R) mix specimens, the compressive strength for temperature rate of 600 C° shown in

Table (16) decreased to 31.01% and 41.25% at an ages of 60 and 90 days respectively, compared to

0

20

40

60

0 10 20 30 40 50 60 70 80 90 100

Co

mp

ress

ive

Str

en

gth

, M

Pa

.

Age, (Days).

R6Mix H6Mix



176

their relatives in Table (15) not exposed to high temperature, and 41.32% and 48.39% for

temperature rate of 1000 C° at ages of 60 and 90 days respectively. It has noted that for (H) mix

specimens, the compressive strength for temperature rates of 600 C° shown in Table (16) decreased

to 37.69% and 40.49% at ages of 60 and 90 days respectively compared to their relatives in Table

(16), not exposed to high temperature, and 47.55% and 48.26% for temperature rate of 1000 C° at

ages of 60 and 90 days respectively due mainly to the alteration of the porous network (Departure of

bond water and decomposition of hydrates and to microcracking)

Fig. (4): Variation of residual compressive strength versus temperature exposure at age of

60days

Fig. (5): Variation of residual compressive strength versus temperature exposure at age of 90

days

Table (16): Residual compressive strength results of R and H mixes versus exposure

to elevated temperature rates

Age,

(Days) Temperature, (C°)

Compressive

Strength of

R6 Mix,

MPa

Compressive

Strength of

H6 Mix,

MPa

% of

Difference

R and R6

Mixes

% of

Difference

H and H6

Mixes

% of

Weight

Loss of

R6 mix

% of

Weight

Loss of H6

mix

90

0 43.85 51.00 0.00 0.00 0.00 0.00

150 40.56 46.00 -7.50 -9.80 -1.61 -2.59

400 45.11 48.86 2.87 -4.20 -3.23 -2.10

600 30.25 31.78 -31.01 -37.69 -7.41 -9.29

1000 25.73 26.75 -41.32 -47.55 -8.31 -9.07

180

0 51.64 53.00 0.00 0.00 0.00 0.00

150 46.63 48.73 -9.70 -8.06 -6.24 -2.89

400 48.12 50.45 -6.82 -4.81 -7.04 -1.23

600 30.34 31.54 -41.25 -40.49 -9.49 -8.77

1000 26.65 27.42 -48.39 -48.26 -14.18 -8.92



177

7.3) Flexural Toughness

7.3.1) (R) Sample

The fiber reinforced concrete not only shows its effect on the pre-cracking state, but also it is

vital in the post-cracking state leading to an increase of ductility for fiber reinforced concrete after

the first crack of concrete.

Evidence showed that specimens containing no fibers could not sustain any load and failed

suddenly when the first crack was developed and hence the toughness index for these specimens at

all ages of curing is equal to 1. However, fiber reinforced concrete has the ability of energy

absorption to the fibers after the first crack appears when it tends to hold the concrete prism together,

without causing it to break into two parts. In general, the toughness index for the fiber reinforced

concrete varied greatly depending on the fiber type and the distribution of the fibers.

As the deformation of the concrete prism increased, the load capacity of the fibers was

decreased. According to Figs. (7) and (8), it is noted that the flexural strength increased with age, and

when the sample is subjected to increase in temperature exposure the behavior varies, so upon

exposure to 450 C°, there is a considerable increase in ultimate load and then there is a decrease

upon temperature exposures of 600 and 1000 C°. It is noted in Fig. (9), that the behavior is similar to

that of the age of 60 days but with small rates of deflection and this is due to continuous hydration

which results in robust microstructure that can sustain loads.

Fig. (6): Load-Deflection curves of R6 mix versus curing age

Fig. (7): Load-Deflection curves of R6 mix at age of 60 days versus temperature exposure



178

Fig. (8): Load-Deflection curves of R6 mix at age of 90 days versus temperature exposure

7.3.2(H) Sample

Fig. (9), shows Load-Deflection Curves of H6 Sample at 5 different ages were planned to

study the flexural strength of sample increased with increase in age. Fig. (10) shows load-deflection

curves of H6 sample at the age of 60 days and exposed to temperature raise and as shown in the

figure, the curves are interfered but the one exposed to 600 C° has the lesser value of ultimate load

and an improvement in sustaining flexural load was upon 450 C°, at which a partial improvement in

mechanical properties was noted. Load-Deflection curves of H6 sample at an age of 90 days are

showing in Fig. (11), and by compare results with ones in Fig. (10), the difference is well illustrated

under the same temperature conditions.

Fig. (9): Load-Deflection curves of H6 mix versus curing age

Fig. (10): Load-Deflection curves of H6 mix at age of 60 days versus temperature exposure



179

Fig. (11): Load-Deflection curves of H6 mix at age of 90 days versus temperature exposure

8- CONCLUSIONS

On the basis of results of this investigation the following conclusions may be deducted:-

1. It is possible to produce a light weight aggregate carbon fiber concrete with a dry density

ranged between (1820) to (1950)Kg/m3 the addition of (SF) does not affect the density

significantly.

2. The required dosage of superplasticizer (SP) for carbon fiber LWAC increases with

increasing the percentage volume fraction of fiber. The useful dosage range is (4 to8%)

3. The addition of carbon fiber to (SF) light weight concrete increases slightly the compressive

strength. Also the compressive strength increases with increasing volume fraction of carbon

fiber.

4. The effect of Silica fume, carbon fiber addition, and heat treatment temperature on flexural,

tensile and compressive strength of porcelinite lightweight concrete was investigated

experimentally.

5. The Analysis by SEM revealed the existence of C-H Crystals at early ages and the

development of C-S-H Crystals gel with age. Also, the SEM showed the improvement of

microstructure of FRSCC composites containing HRWRA and Mineral admixtures, and due

to the effects of rate of hydration the gel products were increased and C-H crystals decreased

with age of specimen.

6. The Micrograph of Microstructure revealed smooth dense contact at interface transition zone.

The development of bond strength within the transition zone of fiber/matrix was done at

earlier stage with superplactizer and mineral admixture, which eliminated the weakness

points within the transition zone.

7. The SEM photograph shows that the distributions of PP fibers within FRSCC were randomly

oriented.

REFERENCES

[1] Dhir, K., Mays, R.G.C and Chua, H.C., "Lightweight Structural Concrete with Aglite

Aggregate: Mix Design and Properties", The International Journal of Cement Composition

and Lightweight Concrete, Vol. 6, No. 4, November 1984; pp. 249-261.

[2] AL-Haddad, M. Y., "Durability of Lightweight Porcelinite Concrete Containing Slag

Exposed to Solution of Sulfates and Chlorides", M.Sc. Thesis, University of Technology,

August 2000.



180

[3] AL-Timimy, B. A., "Improvement of the Durability of Glass Fiber Reinforced Concrete",

M.Sc. Thesis, University of Technology, April 2001; pp. 160.

[4] Zeng, Q. and Chung, D. D., "Carbon Fiber Reinforced Cement Composites Improved by

Using Chemical Agents", Cement and Concrete Research, Vol. 19, 1989; pp. 25–41.

[5] ASTM C192/C192M–02, "Standard Practice for Making and curing Concrete Test

Specimens in the Laboratory", Annual Book of ASTM Standards, Vol. 04.02, 2004;

pp. 126–133.

[6] Dr. V.Bhaskar Desai and A.Sathyam, “Basic Properties of Artificial Lightweight Aggregate

by using Industrial by Product (Fly Ash)”, International Journal of Civil Engineering &

Technology (IJCIET), Volume 5, Issue 6, 2014, pp. 65 - 72, ISSN Print: 0976 – 6308,

ISSN Online: 0976 – 6316.

[7] Javaid Ahmad and Dr. Javed Ahmad Bhat, “Flexural Strengthening of Timber Beams using

Carbon Fiber Reinforced Polymer Plates”, International Journal of Civil Engineering &

Technology (IJCIET), Volume 4, Issue 5, 2013, pp. 61 - 77, ISSN Print: 0976 – 6308,

ISSN Online: 0976 – 6316.

[8] Ghassan Subhi Jameel, “Study The Effect of Addition of Wast Plastic on Compressive and

Tensile Strengths of Structural Lightweight Concrete Containing Broken Bricks as Acoarse

Aggregate”, International Journal of Civil Engineering & Technology (IJCIET), Volume 4,

Issue 2, 2013, pp. 415 - 432, ISSN Print: 0976 – 6308, ISSN Online: 0976 – 6316.

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