12

CHAPTER 2

REVIEW OF LITERATURE

2.1 INTRODUCTION

In this chapter, a brief review of literature on influence of mineral

admixtures on the strength and durability aspects such as saturated water

absorption, sorptivity, corrosion resistance and acid resistance of high

performance concrete is reported and discussed. The literature review of

behaviour of structural members such as beam and column is also presented.

A thorough literature review of the new techniques of strengthening

reinforced concrete by externally bonded FRP composites from available

literature is also presented in this chapter.

2.2 INFLUENCE OF MINERAL ADMIXTURES ON

CONCRETE

2.2.1 General

In the present study, the mineral admixtures such as SF,MK and FA

are used for producing HPC. Silica fume is a by-product of the fabrication of

silicon metal, ferrosilicon alloys and other silicon alloys. Since, the particles

of silica fume are very small, they can enter the space between the cement

particles and thus improve packing. Metakaolin derived from purified kaolin

clay, is a white, amorphous, alumino-silicate, which reacts aggressively with

calcium hydroxide, a normal cement hydration by-product, to form

compounds with cementitious value. It provides superior pozzolanic

13

performance that contributes to the improved strength, durability, chemical

resistance, water absorption, efflorescence control, and aesthetics for quality

concrete and cement based materials. The literatures regarding the influences

of these mineral admixtures on the properties of concrete in the fresh and

hardened stage are discussed.

2.2.2 Properties of admixtures in HPC

For silica fume concrete at a constant water binder ratio (w/b) of

0.34 and replacement of cement up to 25 percentages with varying dosages of

chemical admixture, a maximum 28 days compressive strength can be

obtained at 15% replacement level as reported by Yogendran et al (1987).

Hassan et al (2000) studied the effect of mineral admixtures on

short and long term properties of high performance concrete. The concrete

mixes made with different binders (OPC, OPC/SF, OPC/FA) were prepared.

For the silica fume and fly ash concrete mixes 10 % and 30% by weight of the

Ordinary Portland Cement (OPC) were replaced by silica fume and fly ash

respectively. The water cement ratio was 0.32, 0.32 and 0.29 respectively for

the OPC, OPC/SF and OPC/FA concrete mixes.

It was concluded that silica fume enhances the early age strength as

well as the long term properties of concrete. It reduces the permeability by 71

and 87% at 1 and 365 days respectively, when compared to OPC concrete.

Fly ash concrete has relatively poorer characteristics at early age but achieves

less or equal strength in long term. Using cube size of 100 mm compressive

strength of high performance concrete was studied for different concrete

mixes up to 1 year.

The performance characteristics of high strength concrete having

ultimate compressive strength of 50 to 70 MPa is studied by Natesan et al

14

(2000). From the test results it was concluded that high performance concrete

has superior characteristics when compared to normal cement concrete.

Edward and Charles (2001) studied the strength and durability

response of cement replacement mixtures containing slag, silica fume and fly

ash. It is concluded that concrete mixtures replacing between 31 and 60

percent of portland cement with pozzolans and alternative cements can

achieve compressive strength of 100 MPa at age of 90 days.

The addition of silica fume in plain concrete up to 7.5 per cent

improves the mechanical properties of concrete both at 7 and 28 days as

reported by Ganesan and Sekar (2003). Ravindra and Narasimhan (2003)

observed that the addition of 11.5% silica fume, as a partial replacement to

cement leads to maximum gain in compressive strength and beyond this limit

the strength decreased.

Venkatesh Babu and Krishnamoorthy (2005) studied that the silica

fume concrete and cement replacement level of 10 percentage silica fume in

concrete mixes showed a compressive strength of 61.28 MPa at the age of 28

days and 81.5 MPa at the age of 90 days. When 15 percentage of silica fume

used in concrete mixes, the compressive strength of concrete at 28 and 90

days decreased to a lower value.

2.2.3 Influence of admixtures on fresh concrete

It is essential that silica fume be dispersed uniformly in the mix.

The very large surface area of the particles of silica fume, which have to be

wetted, increase the water demand so that, in mixes with low water/cement

ratio, it is necessary to use super plasticizer for workability. But the

effectiveness of super plasticizer is enhanced by the presence of silica fume.

The presence of silica fume affects significantly the properties of fresh

15

concrete. The mix is strongly cohesive and hence reduces or even stops

bleeding. But reduced bleeding can lead to plastic shrinkage cracking under

drying conditions. The cohesiveness of concrete containing silica fume makes

it satisfactory for pumping and underwater concreting, as well as for use as

flowing concrete.

Jatren (1983) reported that fresh concrete containing silica fume is

more cohesive and less prone to segregation than concrete without silica

fume. Scali et al (1987) reported that the water demand of concrete containing

silica fume increases with increasing amount of silica fume at the fresh stage

of concrete.

Hossam and Tahar el-Korchi (1995) were of the view that the

optimum benefit of the addition of silica fume is attained when it is used in

combination with super plasticizers. This combination increases the

cohesiveness of the fresh composites and reduces the water content.

Zhang and Malhotra (1995) indicated that the quantity of super

plasticizer required for 10% metakaolin (MK) incorporated is same as that of

silica fume concrete but setting times of silica fume concrete is faster than

metakaolin concrete. Wild et al (1996) found that cement replacement by MK

at 20% enhances the maximum strength whereas SF needs at least 28%

replacement to attain same level of strength.

Khatib and Wild (1998) investigated the resistance of MK mortar to

sodium sulphate (Na2SO4). MK produces a reduction in CH content of cement

mortars and refinement of pore structures which improves the sulphate

resistance. The magnitude of expansion is controlled by the availability of

C3A content in mortars. At high MK contents (15-25%) CH availability is

restricted so that magnitude and rate of expansion is very much smaller.

Duval and Kadir (1998) studied the effect of silica fume on the heat of

16

hydration of high performance concrete and concluded that the addition of

silica fume counteracts the retarding effect of the super plasticizer on cement

hydration. In the early ages, silica fume accelerates the rate of heat evolution.

The pozzolanic reaction takes place early and plays an important role on the

heat of hydration at the fresh stage.

Pinto and Haver (2000) noted that reductions in cement content and

increment in super plasticizer dosage tend to retard setting, while increases in

silica fume tend to accelerate setting.

Xiaoqian Qian and Zongijin Li (2001) concluded that the tensile

strength and peak strain increases with increased metakaolin content whereas

the tensile elastic modulus shows only small changes. The descending area of

over-peak stress is improved when 5% and 10% of cement is replaced by

metakaolin. Also, the flexural strength and compressive strength increase with

increasing metakaolin content. The compressive elasticity modulus of

concrete showed a small increase with increasing metakaolin replacement.

The compressive strength increases substantially at early ages, and there is

also higher long term strength.

Yunxing et al (2002) reported that partial replacement of cement

with silica fume can improve the fluidity and rhelogical property of HPC.

Santanu Bhanja and Bratish Sengupta (2002) carried out a

comprehensive study intended to determine the contribution of silica fume on

concrete over a wide range of w/b ratio ranging from 0.26 to 0.42 and cement

replacement up to 30 percentages. Viviana and Osar (2004) highlightened the

benefits of adding mineral admixtures such as natural pozzolan, fly ash and

silica fume to control heat of hydration development.

17

Khatib (2008) found that at a low water to binder ratio of 0.3, the

optimum replacement level to give maximum strength enhancement is 15 %

MK. This optimum level is lower than that obtained at higher water to binder

ratio of 0.45. The maximum contribution of MK to strength occurs at 14 days

of curing, which is similar to results obtained at higher water to binder ratio. It

was observe that the systematic increase in MK content of up to 20% in

concrete leads to a decrease in shrinkage and an increase in expansion after 56

days of curing.

2.2.4 Role of silica fume on HPC

High Compressive strength is generally the first property associated

with silica fume concrete. The report by Sellevold and Radjy (1983) shows

that the addition of silica fume to a concrete mix will increase the strength of

that mix by around 30 to 100% depending on the type of mix, type of cement,

amount of silica fume, use of plasticizers, aggregate types and curing regimes.

Silica fume concrete is very susceptible to temperature variations during the

hardening process.

Wolsiefer (1984) reported that for 98 MPa concrete containing

593 kg/m3 of cement and 20% of silica fume, the ratio of flexural to

compressive strength varied between 0.13 to 0.15

Feldman and Cheng-yi (1985) and Cohen (1990) studied and found

that there are three mechanisms namely (i) strength enhancement by pore size

refinement and matrix densification,(ii) strength enhancement by reduction in

CH content and (iii) strength enhancement by cement paste aggregate

interfacial refinement believed to be responsible for the strength development

of concrete because of mortars containing silica fume.

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Luther and Hansen (1989) found the modulus of rupture of silica

fume concrete made with dolomite coarse aggregate and having compressive

strength between 51 to 107 MPa to be about 12.3 times the square root of

compressive strength. Larbi and Bijen (1990) explained that silica fume tends

to affect the pattern of crystallization and degree of orientation of CH crystals

at the aggregate surface during the first few days of cement hydration. At a

higher w/b ratio of 0.45 with 30% silica fume, the pastes exhibit higher

strength between 1 day and 180 days.

Bentz and Garboczi (1991) concluded that strength development in

silica fume concrete is much earlier than with portland cement alone. The

contribution of silica fume to the early strength development upto 7 days is

probably through improvement in packing, that is acting as filler and

improvement of the interface zone with the aggregate.

Mc Donald and James (1991) reported that splitting tensile strength

at various ages ranged from 5.8 to 8.2 percent of the compressive strength of

the same age. Bayasi and Zhou (1993) found that the addition of silica fume

enhances the rate of cement hydration at early hours due to release of OH-

ions and alkalis in the pore fluids. Silica fume accelerates both C3S and C3A

hydration during the first few hours.

Hooton (1993) demonstrated that the high early reactivity of silica

fume and the dense microstructure of the hydrated cement paste make it

difficult for water to enter from outside, if available, to penetrate towards the

unhydrated portion of portland cement and silica fume particles. Calcium

silicate hydrates (C-S-H) plays a vital role in pastes with silica fume, due to

both CH and non-evaporable water contents at the early ages of 3 and 7 days.

However, the hydration reactions in mortar terminate earlier. After 28 days,

the non-evaporable water content continues to increase significantly in plain

cement concrete as reported by Mak et al (1995).

19

Ganesh Babu and Surya Prakash (1995) reported that the efficiency

of silica fume depends on the replacement levels. Joshi (2001) was of the

opinion that the compressive strength of 75.16 MPa at the age of 28 days for

M 60 grade concrete mixes (with w/b ratio 0.35 and with 10% replacement of

cement by silica fume) can be used for the construction of Bandra-Worli sea

link four lane bridge.

Hassan et al (2000) concluded that silica fume enhances the early

age strength as well as the long term properties of concrete. It reduces the

permeability by 71% and 87% at 1 and 365 days respectively, when compared

to OPC concrete. Fly ash concrete has relatively poorer characteristics at early

age but achieves more or less equal strength in long term.

Khan and Lyssdale (2002) reported that the incorporation of silica

fume content increases the early strength, but 8-12% silica fume yielded the

optimum strength values. It was also indicated that silica fume in concrete is

an efficient pozzolanic material which improves the impermeability of the

structure when compared to plain cement concrete.

Nakin Suksawang et al (2006) reported that adding silica fume to

HPC increases both the compressive strength and the modulus of elasticity at

early ages. However, the increase subsides at later ages (> 28 days). On the

other hands, adding fly ash to HPC reduces both the compressive strength and

the modulus of elasticity at early ages, but they increase at later ages. HPC

containing combination of silica fume and fly ash behaves similar to HPC

containing silica fume.

2.2.5 Effects of metakaolin on HPC

Andriolo and Sgaraboza (1986) reported that the incorporation of

metakaolin improves the strength of concrete significantly. The results of

20

their work indicated that the optimum level of replacement lie somewhere

between 5 and 10 percent. Palomo and Glasses (1992) confirmed that the

partial replacement of metakaolin contributes to the strength of concrete due

to the filler effect, the acceleration of hydration of cement and due to the

pozzolanic reaction.

Xiaoqian Qian and Zongijin Li (2001) were of the view that MK is

a very efficient strength enhancing additive and at higher MK contents

workability can be controlled effectively by superplasticizer additions. For the

w/b ratio 0.3, the 10% replacement by weight of cement yields maximum

strength and for other trial tests, strength increases even with 15% metakaolin

as reported by Shreeti and Prabir (2003).

2.2.6 Influence of fly ash on fresh concrete

The cement replacement level of 25% with fly ash (class F) in

concrete mixes is found to be the optimum level to get the compressive

strength of 80 MPa at 28 days. The concrete mix with 25% fly ash content as

cement replacing material had the lowest value of saturated water absorption,

sorptivity and chloride diffusion when compared with that of the control

concrete mixes as reported by Gopalakrishnan et al (2001).

2.3 STRENGTH CHARACTERISTICS OF HIGH

PERFORMANCE CONCRETE

2.3.1 General

In high performance cement paste with a varying low water/binder

ratio, hydration stops within the concrete long before 28 days due to lack of

water or when the partial pressure of water vapor within the pores reached the

80% limit below which hydration is slowed down very significantly. Aitcin

and Laplante (1990) found out that some high performance concrete

21

laboratory specimens experienced a slight decrease in compressive strength

after a long period of curing in air, particularly that containing silica fume.

2.3.2 Effect of admixtures on high performance concrete

High compressive strength is generally the first property associated

with silica fume concrete. Yogendran et al (1987), Hooton (1993) and Sabir

(1995) reiterated that the strength development in concrete with condensed

silica fume is higher in the range of 12-28%. Cong and Darwin (1992)

reported that lower compressive strengths were achieved at the age of 3 days

while higher strengths at 7 and 28 days with silica fume mortars.

Ohja and Nasser (1996) recommended that the maximum

percentage replacement of silica fume is 10-15% of total binder content by

weight. Amit Mittal and Kamath (1999) obtained compressive strength of

75.9 MPa at the age of 28 days for M60 grade concrete mixes (with w/b ratio

0.32 and with 7.5% replacement of cement by silica fume) which was used

for the construction of primary containment dome of the nuclear power plant

at Kaiga, Karnataka state, India.

Shannag and Hussain (2003) reported that high and very high

strength concrete can be achieved with 15% silica fume and 15% natural

pozzolana. Sinan Caliskan (2003) explained that 20% silica fume replacement

with cement and addition of super plasticizer to the mortar produce a thinner

interfacial zone with the plain cement mortar due to silica fume densities. The

microstructure acts as filler as well as provides secondary hydration products,

while superplastizer provide deflocculation of the cement and silica fume

particles. Venkatesh Babu et al (2004) found that the cube compressive

strength of the order of 55.25 to 76.5 MPa can be achieved at the age of 28

days for concrete mixes (with water binder ratio 0.32) containing 0-15%

replacement of cement by silica fume.

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2.4 DURABILITY CHARACTERISTICS OF HIGH

PERFORMANCE CONCRETE

2.4.1 General

One of the principal reasons for the deterioration of many concrete

structures stems from the fact that, in the past and even now, too much

importance has been given to concrete compressive strength when designing

concrete structures and not enough to the environmental factors that the

structure will have to face while performing its structural function. However,

in recent years a new attitude has been perceived towards durability in various

national codes of India, Japan, Australia, Europe (Rostam and Schissel, 1993)

and Canada. When looking at concrete from the durability point of view, it

has been found that the high slumps achieved when using superplasticizers

create a new type of heterogeneous zone along the forms or at the top surface

of the concrete. This zone has become known as the �Concrete skin�

(Kreijger, 1987), �Outer skin� (Bentur and Jaegermann, 1991), simply as

�covercrete�. Parrot (1992) recognized the importance of concrete skin (the

outermost 5 to 10 mm) from the durability point of view, inspite of the fact

that the concrete skin does not have exactly the same composition and

microstructure as the interior of concrete, owing to the so-called �wall effect�.

When a high performance concrete is plastified its slum is maintained, there is

a little risk of segregation, because the mix is quite rich and quite thioxitropic,

but it is observed that the wall effect is greatly increased when the slump

increases. The use of permeable forms seems to be an option very often used

in Japan (Katayama and Kabayasi, 1991) to improve the durability and

aesthetics of concrete skin.

23

Maage (1987) investigated water permeability, frost resistance,

surface attack, carbonation, chloride ion diffusion, pH level of pore water and

electrical resistivity and concluded that silica fume worked in combination

with blended cements in approximately the same manner as with concretes

containing only portland cement. During and Hicks (1991) reported that from

the comparison of various mineral additives used in concrete structures, silica

fume is highly favoured for its superior concrete durability properties.

Shannag and Hussain (2003) reported that among HPC that

contains silica fume and natural pozzolan can provide a good balance between

strength and durability. The influence of silica fume on permeability is more

than that on compressive strength. The reduction in the diffusivity of

chlorides due to the presence of silica fume in hydrated cement paste is larger

at water/cement ratio greater than 0.4. The sulphate resistance of concrete

containing silica fume is good, partly because of a lower permeability, and

partly in consequence of a lower content of calcium hydroxide and of

alumina, which have become incorporated in C-S-H. Silica fume is

particularly very effective in controlling expansive alkali-silica reaction.

Shrinkage of concrete containing silica fume is some what more than in

portland cement concrete.

2.4.2 Effect of mineral admixtures on saturated water absorption

Ramakrishnan and Srinivasan (1983) opined that the water

absorption co-efficient of silica fume fibre reinforced concrete is lower than

that of an ordinary fibre reinforced concrete. Sellevold and Radjy (1983)

noted that the absorption of water in concretes containing silica fume was

much lower than that of reference concrete.

Lehtonen (1985) concluded that the silica fume concrete showed a

more gradual rate of water absorption despite the fact that both types of

24

concrete had attained a similar degree of saturation. Bharatkumar et al (2001)

reported that the effect of mineral admixture on the strength of concrete varies

significantly with its properties and replacement levels. They obtained water

absorption of the order of 2.90 to 4.78% for concrete mixes containing cement

replacement materials.

2.4.3 Effect of mineral admixtures on sorptivity

Venkatesh Babu et al (2004) came out with a conclusion that

porosity and sorptivity were in the order of 1 to 1.35% and 1 to

3.54 mm/min0.5

, respectively, for concrete mixes containing 10 to 15% of

cement replacement by silica fume.

2.4.4 Effect of mineral admixtures on acid resistance

Venkatesh Babu et al (2004) observed a lower range of weight loss

for concrete mixes containing 2.5 to 15% replacement of cement by silica

fume.

2.5 MIX PROPORTIONING FOR HIGH PERFORMANCE

CONCRETE

The mixture proportioning method for high performance concrete

only provided a starting mix design that will have to be more or less modified

to meet the desired concrete characteristics.

Mehta and Aitcin (1990) proposed a simplified mix proportioning

procedure that is applicable for normal weight concrete with compressive

strength values between 60 and 130 MPa. Aitcin (1990) proposed a very

simple method which can be used for both air entrained and non-air entrained

HPC.

25

The ACI 363 committee (1997) proposed a mix design for high

strength concrete in which the maximum size of aggregate suggested was 19

or 25 mm for concrete with strength less than 65 MPa and 10 to 13 mm for

concrete made with strength greater than 85 MPa. The formula has been

suggested to find the dry weight of coarse aggregate. A computerized

program has been developed from this method and is currently used in France

under the trade name of BETONLAB (Sedran et al 1996). Francois De

Larrard and Thierry Sedran (2002) proposed a mix proportioning for high

performances concrete considering packing density and segregation ability of

dry packing particles. They focused on the properties of fresh concrete and

the mechanical properties of hardened concrete using a model of aggregate

particles surrounded by cement�based matrix. The practical example is also

presented, dealing with the design of special HPC for pavement application.

2.6 BEHAVIOUR OF HPC BEAM CONFINED WITH FRP

Hadi (2003) carried out experimental investigation on sixteen

number of shear beams specimens which were retrofitted by using various

types of fibre reinforced polymer (FRP) and reported that there are several

parameters that affect the strength of the beams. The results also exhibited

that the use of FRP composites for shear strengthening provides significant

static capacity increase.

Riyadh Al-Amery and Riyadh Al-Mahaidi (2006) carried out an

investigation on six numbers of RC beams having various combinations of

CFRP sheets and straps in addition to an unstrengthened beam as control test.

Test results and observations showed that a significant improvement in the

beam strength is gained due to the coupling of CFRP straps and sheets.

Saafan et al (2006) investigated the efficiency of GFRP composites

in strengthening simply supported reinforced concrete beams designed with

26

insufficient shear capacity and indicated that significant increases in the shear

strength and improvements in the overall structural behaviour of beams with

insufficient shear capacity could be achieved by proper application of GFRP

wraps.

2.7 BEHAVIOUR OF COLUMN

Arunachalam and Sabapathi (2004) studied the behaviour of HSC

square short columns subjected to axial loading with respect to the variation

in the degree of confinement introduced by changing the diameter of the

lateral ties and their spacing and compared the same with normal strength

concrete (NSC) columns. It is found that confinement of HSC columns

increases the ductility, load carrying capacity and energy absorption capacity

of otherwise brittle HSC Columns.

Chien-Hung Lin et al (2004) studied the behaviour of high

workability columns (HWC) and normal concrete columns under concentric

compression and came out with a conclusion that HWC columns have higher

stiffness, better ductility and crack control ability than normal concrete

columns. A decrease in concrete strength, increase of longitudinal

reinforcement, increase of transverse reinforcement strength, and decrease of

transverse reinforcement spacing improve the ductility of confined concrete

and columns effectively.

2.8 BEHAVIOUR OF CONCRETE ELEMENTS CONFINED

WITH FRP

Haroun et al (2002) tested seven rectangular RC columns repaired

with crack injection and carbon fibre jacket with steel transverse steel

reinforcement under reversed cyclic load. The repaired column specimens

performed in a ductile response compared to the as built one.

27

Teng and Lam (2002) reported that the axial compressive strength of

FRP confined concrete in elliptical specimens is controlled by the amount of

confining FRP and the major to minor axis length ratio a/b of the column section.

Toutanji and Deng (2002) reported that the aramid fibre reinforced

polymer composite sheets constrains the lateral strain, producing a tri-axial

stress field in concrete, which results in improving the compressive strength,

maximum strain and ductility. Ye et al (2002) tested seven square short

concrete columns strengthened with CFRP under lateral cyclic loading and

concluded that strengthened specimens had a more ductile behaviour

compared to the unstrengthened ones.

Azadeh Parvin and Aditya Jamwal (2005) reported that the axial

stress and axial strain carrying capacities of the FRP wrapped concrete

columns increased significantly as compared to the unconfined column and

also reported that the increase in wrap thickness resulted in enhancement of

axial strength and ductility of the concrete columns. For the FRP wrapped

columns, the axial stress carrying capacity increased with the increase in the

wrap thickness. The axial stress carrying capacity of FRP wrapped circular

columns increased with the increase in concrete strength for a constant wrap

thickness.

Galal and Arafa Ghobarah (2005) found that short columns suffered

brittle shear failure even designed according to current codes and anchoring

of the fibre wraps to the columns was found to be effective in increasing the

shear resistance and energy dissipation capacities of the columns. Hadi (2005)

investigated the behaviour of plain concrete columns reinforced with FRP

both in the vertical and horizontal directions. The performance of the GFRP

wrapped columns was slightly better than the reference columns. Under

eccentric loads, the CFRP columns out performed both the GFRP and the

steel reinforced columns.

28

Vishnuram et al (2006) reported that the repair of damaged

columns by GFRP jackets imparted ductility and enhanced their seismic

behaviour. It was also reported that large number of GFRP layers required for

the columns subjected to higher axial forces.

Hadi (2007) conducted experiment on seven columns which were

eccentrically loaded and reported that the performance of GFRP wrapped

column was slightly better than the reference columns. Rajamohan and

Sundarraja (2007) opined that significant increase in strength and ductility of

concrete could be achieved by glass fibre composite jacketing.

Yousef and Al-Salloum (2007) investigated square concrete column

specimens confined with FRP composite laminates and stated that the FRP

jacket increased both the axial load capacity as well as the ultimate concrete

compressive strain. Kumutha et al (2007) reported that the effective

confinement with GFRP composite sheets resulted in improving the

compressive strength. Better confinement was achieved when the number of

layers of GFRP wrap was increased, resulting in enhanced load carrying

capacity of the column, in addition to the improvement of the ductility. The

load carrying capacity of the column decreased, with increase in aspect ratio

of the cross-section.

Rajamohan and Sundarraja (2007) stated that increase in strength

and ductility of concrete can be achieved by glass fibre composite jacketing

and the ultimate condition of the confined concrete was determined by the

rupture of the composite jacket. Yung-Chih Wang and Hsu (2009) conducted

experiment on column strengthened with GFRP and they were tested under

concentric loading. The results from the tests confirmed that FRP jackets

provided excellent confinement in rectangular and square reinforced concrete

columns, increasing both the ultimate strength and strain.

29

Promis et al (2008) found that the rigidity of FRP reinforcement is

the principal parameter for the increase of damage capacity. Their results

showed that the fully wrapped columns present the same embedded, rigid,

solid behaviour, while the reinforcement by bands induces multi-cracking

around several rigid solids corresponding to the bands of FRP reinforcement.

Riad Benzaid et al (2008) concluded that the number of layers of

FRP materials and the corner radius are the major parameters, having a

significant influence on the behaviour of specimens. Bonding hoop FRP to the

column surface enhances axial load capacity and ductility of columns and also

stated the GFRP materials can produce a good lateral confinement pressure to

column specimens. Then it can be used for strengthening or repairing of

structures.

2.9 ARTIFICIAL NEURAL NETWORK

Cladera and Mari (2004) conducted a study on concrete beams

using an Artificial Neural Network to predict the shear strength of reinforced

beams failing on diagonal tension and, based on its results, a parametric study

was carried out to study the influence of each parameter affecting the shear

strength of beams with web reinforcement. It is observed that the new

expressions correlate much better with the empirical tests than ACI

procedures.

Cahit Bilim et al (2009) carried out a study for predicting the

compressive strength of ground granulated blast furnace slag using artificial

neural networks and concluded that ANN can be an alternative approach for

the predicting the compressive strength of ground granulated blast furnace

slag concrete using concrete ingredients as input parameters.

30

Emre Sancak (2009) reported that the bond strength values

predicted by applying ANN method were found to be close to the bond

strength values obtained via tests. It was concluded that quite beneficial

results can be obtained by ANN to predict the bond strength of normal and

lightweight concrete.

Mustafa Saridemir (2009) studied the models in artificial neural

networks (ANN) for predicting compressive strength of concretes containing

metakaolin and silica fume developed at the age of 1, 3, 7, 28, 56, 90 and 180

days. The training and testing results in the neural network models have

shown that neural networks have strong potential for predicting 1, 3, 7, 28, 56,

90 and 180 days compressive strength values of concretes containing

metakaolin and silica fume.

Zohra Dahou et al (2009) proposed a model in ANN for predicting

the bond between conventional ribbed steel bars and concrete and the results

indicated that implemented models have good prediction and generalisation

capacity with low errors. Mostafa Erfani and Ehsan Noroozinejad Farsangi

(2010) explained that the trained system in ANN have strong potential

capability to predict compressive strength of mortars containing ground

granulated blast furnace slag.

Various researchers have proposed several neural network models

for mix design and predicting the concrete properties such as compressive

strength, slump etc., Lai and Sera (1997) and Lee (2003) developed a neural

network based model to predict the compressive strength of conventional and

high strength concrete. Udhayakumar et al (2007) concluded that a neural

network based strength prediction model can be used successfully to find out

the strength development of the fly ash concrete with the age of concrete. It

was proved that the neural network based strength prediction model can be

successfully used to predict the strength of concrete for various mix

31

proportions. It can also be used to obtain the strength development of the

concrete mix with the age of the concrete.

2.10 FINITE ELEMENT MODELLING

Ben young and Jintang Yan (2002) performed finite element

analysis on fixed ended cold formed plain channel columns and predicted the

ultimate load and failure modes of the tested columns.

A finite element study on RC beams was carried out by Revathi and

Devdas Menon (2005) and concluded that predicted results from ANSYS are

found show good agreement with the physical experiments. Elyasian et al

(2006) reported that the FRP strengthened RC beams exhibited results in good

agreement with previously published test results when modelled using

ANSYS and therefore it can be confidently used in design and analysis

situations.

ANSYS study on retrofitted RC beams under combined bending

and torsion was carried out by Santhakumar et al (2007) and concluded that

FRP composites wrapped around the beams are effectively utilized in

improving the load carrying capacity with increase in the twisting moment to

bending moment ratio. Balamuralikrishna and Antony Jeyasehar (2009)

conducted a test for the flexural behaviour of beams strengthened with CFRP

and tested by monotonic and cyclic loads. These results are compared with

ASNSYS results and found that strengthened beams exhibit increased flexural

strength, enhanced flexural stiffness, and composite action until failure.

2.11 NEED FOR THE PRESENT STUDY

From the foregoing discussions, it is obvious that the use of

minerals (SF, MK and FA) for replacement of cement is an urgent need to

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cope with the shortfall in the supply of cement. Further, mineral admixtures

were utilized for making High Performance Concrete (HPC) which will

satisfy the need for the disposal of solid wastes. Apart from environment and

economy, the use of admixtures helps to obtain durable high strength concrete

with minimum cost.

Experiments were conducted on HPC incorporated with mineral

admixtures such as silica fume, metakaolin and fly ash. The strength

characteristics such as compressive strength, split tensile strength and flexural

strength were investigated adopting water binder ratios of 0.3 and 0.32 at

different ages to find the optimum replacement level for cement by mineral

admixtures. With the optimum replacement of cement, the beam specimens

were cast for predicting the structural behaviour in both shear and flexure.

Similarly the columns (short and slender) were cast to study their behaviour

under uniaxial compression. The beam and column specimens were repaired

with glass fibre reinforced polymers after damaging the specimens to an

extent of their first yield load and tested again. Their load carrying capacities

and deflections were compared and reported.