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CHAPTER-8

DISCUSSION OF TEST RESULTS

8.0 INTRODUCTION

The results of the experimental investigations on Low, Medium

and High grade SCC are discussed as follows.

The discussions are classified into seven phases of study. They are

i). Studies on behavior of fresh and hardened properties of low,

medium and high grades of SCC with GGBS.

ii). Studies on effect of partial replacement of Rice Husk Ash in

GGBS SCC mix on its fresh and hardened properties.

iii) Evaluation of strength efficiency factors of GGBS and RHA in

SCC.

iv). Studies on Stress-Strain behavior of SCC with and without steel

confinement.

v). Studies on flexural behavior of different SCC mixes.

vi). Validation of theoretical moment-curvature values.

vii). Studies on the durability of SCC with GGBS and RHA.

8.1 PROPERTIES OF MATERIALS

The cement used is 53 grade cement of specific gravity 3.15.The

fineness modulus of fine aggregate is 2.625, bulk density 1700 kg/m3

and specific gravity 2.59 indicating that it is fine sand. The coarse

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aggregate used is of fineness modulus 6.64, bulk density 1560 kg/m3

and specific gravity 2.61.

The admixture is used not to improve the quality of concrete but

to modify the properties of concrete as per special requirements.

GGBS and RHA are the mineral admixtures used in the present study,

apart from chemical admixtures. The GGBS generally reduces the

water demand and improves workability. The factors influencing the

reactivity of GGBS are the chemical composition of slag and the glass

content which is shown in tables 5.1.3.1 & 5.1.3.2. Rice Husk Ash

used is having very high silica content and it is exhibiting high

pozzolanic characteristics contributing to high strength and high

permeability of concrete, these properties are shown in tables 5.1.4.1

& 5.1.4.2. However to achieve adequate workability as well as high

strength in SCC, superplasticisers are necessary, tables 5.1.5.1 &

5.1.5.2 show the properties of superplasticisers used in present

investigation.

8.2. STUDIES ON BEHAVIOUR OF FRESH AND HARDENED

PROPERTIES OF THREE GRADES OF SCC WITH GGBS.

8.2.1. Mix Proportions of Low, Medium and High grade Self

Compacting Concrete with GGBS.

The three grades are designed based on EFNARC method with

coarse aggregate of size 10 mm to get trial mixes. Number of trials is

performed in the laboratory and from these finally design mixes are

arrived. The main investigation is to study the behavior of low,

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medium and high grades of SCC with GGBS and chemical admixtures

like superplasticizers.

During the initial stage of work the cube specimens of the three

grades M20, M40 and M60 are cast with cement replaced by 10% to

35% of GGBS (at an increment of 5% ) and the specimens are tested

for Compressive strength at 3days and 7days. The Compressive

strengths are compared with that of corresponding grade concrete

specimens without GGBS and found that at 30% GGBS replacement

for M20 and M40 grade SCC mixes the strength was maximum, and

for M60 grade SCC mix the maximum strength was achieved when

GGBS replacement was 25%. .

Based on optimum GGBS percentages arrived from 3days and

7days cube Compressive strengths, the strengths of prisms and

cylinders are studied for 20% to 35% of GGBS replacement at an

increment of 5% and the cube strengths are studied for 10% to 35% of

GGBS replacements at an increment of 5%. With 30% replacement of

GGBS the studies are done only on M20 and M40 grade SCC mixes.

As the M60 grade mix with 25% GGBS has not satisfied the required

the fresh properties of SCC like slump test, V- funnel test and L- box

test, 5% of RHA is added for further studies. The mix proportions of

different grades are represented in the form of pie charts 5.3.1 to

5.3.6.

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8.2.2 Fresh Properties of Self Compacting Concrete GGBS Mixes

Fresh properties of self compacting concrete mixes with different

percentages of GGBS are studied. The limits for these parameters as

prescribed by the EFNARC specifications are shown in table 5.9.

These values indicate the basic requirements for self compacting

concrete in fresh state. The results of slump cone test, V-funnel test

and L-box test which represents filling ability, passing ability and

segregation resistance are well within the prescribed EFNARC

specifications given in tables 5.2.1.1 to 5.2.1.3. It is observed that the

GGBS based SCC mixes possess self compacting characteristics in

fresh state. The presence of GGBS in the mix improves workability

and makes the mix more mobile but cohesive. This is the consequence

of a better dispersion of the cementitious particles and of the surface

characteristics of the GGBS particles; however it is more sensitive to

variations in the water content than ordinary cement concrete.

8.2.3 Hardened Properties of Self Compacting Concrete GGBS

Mixes

Hardened properties such as compressive strength, split tensile

and flexural strengths are determined by testing specimens of

standard size as per IS specifications. With the selected GGBS mixes,

cubes, cylinders and prisms of standard size are cast, cured and

tested as per IS 516-1959 and the results are tabulated. These results

are discussed as follows.

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8.2.3.1 Compressive Strength

Cubes of 100 mm size are cast with SCC mixes, cured and tested

as per IS 516-1959 to get compressive strength. The results are shown

in tables 5.4.1.1 to 5.4.1.3 and figures 5.4.1 to 5.4.6. An improvement

of 8.3% & 31.04% in M20 mix and 5.6% & 20.83% in M40 mix was

observed when 7days and 28 days compressive strengths of SCC

mixes produced with 30% GGBS are compared with other mixes

without GGBS. However in case of M60 grade the required target

strength was not achieved when replaced with GGBS, so 5% RHA was

added. Also it is observed that there is decrease in compressive

strength by a maximum of 13% at 3 days for all mixes. This is

because the initial hydration of GGBS is very slow as it depends upon

the breakdown of the glass present in GGBS by the hydroxyl ions

released during the hydration of the Portland cement.

8.2.3.2 Split Tensile Strength

Split tensile strength tests are carried out on cylinders of 150 mm

diameter and 300 mm height using a compression testing machine of

1000 KN capacity as per IS 516-1959. Split tensile strength values at

28 days for the mixes are shown in table 5.6.1 to 5.6.3. The 28 days

tensile strengths of SCC mix with 30% GGBS compared to that of mix

without GGBS is increased by 13.35% in M40 grade, while the tensile

strengths are almost same in M20 grade.

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8.2.3.3 Flexural Strength

Flexural strength tests are carried out on prisms of size 100 X

100 X 500 mm using flexure testing machine of capacity 100 KN as

per IS 516-1959. The results of flexural strength tests are shown in

tables 5.7.1 to 5.7.3.

It is observed that the values of modulus of rupture obtained by

the flexure test for the SCC mixes are higher than the values obtained

by 0.7√fck for conventional concrete of same strength. The increase is

6.7% and 4.4% for M20 and M40 GGBS mixes respectively, thus

indicating a considerable increase in the flexural strength of SCC mix

made with GGBS when compared to ordinary SCC mixes. The flexural

strength variation is shown in fig 5.7.1.

8.3 STUDIES ON EFFECT OF PARTIAL REPLACEMENT OF RHA IN

GGBS SCC MIXES, ITS FRESH AND HARDENED PROPERTIES

8.3.1 Fresh Properties of Self Compacting Concrete GGBS-RHA

Mixes

The 30% GGBS mixes are partially replaced with RHA in M20

and M40 grades and in case of M60 grade 5% RHA is added.

Quantities, fresh properties and hardened properties of self

compacting concrete mixes with partial replacement of RHA are given

in tables 5.8.1 and 5.8.2. The fresh properties are within EFNARC

specifications. The rice husk ash which contains as much as 85-95%

silica is highly reactive. Addition of finely ground RHA with a fineness

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of above 16000 sq.cm/gm improves the microstructure of the

interfacial transition zone (ITZ) between the cement paste and the

aggregate in SCC.

8.3.2 Hardened Properties of Self Compacting Concrete GGBS -

RHA Mixes

Hardened properties such as compressive strength, split tensile and

flexural strengths are determined by testing specimens cast with the

GGBS-RHA mixes,

8.3.2.1 Compressive Strength, Split Tensile Strength and Flexural

Strength

When SCC mixes produced with GGBS-RHA are compared with

other mixes without admixtures the improvement is observed in

compressive strengths. From tables 5.8.1 and 5.8.2 it is observed that

the increase in 7days strength is 8.67%, 8.15% and 2.17%

respectively for M20, M40 and M60 grades respectively whereas the

increase in 28 days strength is 46.35%, 33.63% and 7.6%.

From tables 5.7.1 to 5.7.3 the improvement observed in28 days

split tensile strength is 23%, 14.5% and 8.8% for M20, M40 and M60

grades respectively. Similarly when the increase in 28 days flexural

strength is observed it is found to be 17.3 %, 13.2% and 4.45% more

for M20, M40 and M60 grades respectively when compared with

concrete without GGBS and RHA.

The above observations shows that the increase in strengths is

nominal when compared to SCC mixes produced with only GGBS and

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high when compared with GGBS RHA mixes. This is because of high

or effective reactivity of RHA with GGBS. The percentage increase in

strength increased with increase in the amount of RHA but only up to

some percentage of replacement, at higher percentages fresh

properties are greatly affected and the SCC mixes lost self

compactability. This is because of more water absorbing capacity of

RHA at higher dosages i.e. at 5% and more.

8.3.2.2 Finally eight SCC mixes with and without admixtures which

satisfied properties of SCC in fresh state and gave maximum

compressive strength are selected and taken for further investigations.

These mix proportions along with fresh and hardened properties are

given in tables 5.11.1 to 5.11.3.

8.4 INFLUENCE OF MINERAL ADMIXTURES ON FRESH AND

HARDENED PROPERTIES OF SCC

8.4.1 Fresh Properties of SCC

Self compacting concrete mixes produced with different mineral

admixtures like GGBS and RHA given in tables 5.2.1.1, 5.2.1.3 have

shown good range of test results for slump flow values, V-funnel and

L-Box tests which satisfy the limits prescribed by EFNARC

specifications. Thus SCC of acceptable fresh concrete properties can

be produced with GGBS and RHA with proper proportioning. This not

only reduces the production cost of SCC but also increases the proper

utilization of industrial wastes like GGBS and RHA.

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8.4.2 Hardened Properties of SCC

When hardened properties like compressive, split tensile and

flexural strengths of SCC mixes using mineral admixtures like GGBS

and RHA in different proportions are observed, in general SCC mixes

with GGBS and RHA have shown better performance in hardened

state than SCC mixes without admixtures. In case of GGBS mix due

to the reduced fineness of GGBS resulting in lesser water content and

hence is the improvement in strength and ground to higher fineness

GGBS reduces bleeding of concrete.

Whereas the results indicate that in case of GGBS -RHA mix at

higher dosages of RHA there is no considerable increase in the

compressive strength at early ages but at later ages, the increase was

high, up to 46% for M20 grade and 33.63% for M40 grade

respectively. Whereas the increase was only 7.58% for M60 grade

when compared with ordinary SCC mixes.

Similarly when the improvement in split tensile strength and flexural

strengths are observed the increase is more in case of M20 and M40

grades and improvement is less in case of M60 grade, this may be due

the reason that in case of M60 grade the RHA is added but not

replaced, demanding more water, reducing the strength.

Thus incorporation of sufficient dosages of RHA to GGBS based

SCC mixes, greatly increases the strengths at different ages if the

fresh properties satisfy EFNARC specifications. Therefore can be

concluded that GGBS, RHA and their combinations used in the

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production of SCC greatly influences fresh and hardened properties of

SCC.

8.5 INFLUENCE OF SUPERPLASTICISER ON FRESH AND

HARDENED PROPERTIES OF SCC

Self-compacting concrete incorporates admixtures that

significantly increase the material's workability and fluidity. SCC is

placed with little or no compaction in very heavily reinforced sections,

in inaccessible areas because of easily flowability.

Final mixes produced with mineral admixtures like GGBS and

RHA with different dosages of superplasticizer as given in table 5.11.1.

From the table 5.11.2 it is observed that slump flow values are

between 760-715mm, T50 time is between 4.28-3.08 sec, V-Funnel test

results between 8.68-8.03 seconds and L-Box test results 0.98 to 0.86

for three grades of SCC.

The super plasticizer makes SCC mix workable and offers

fluidity to the mix for the given water-powder ratio. This quantity

plays an important role in SCC, because if the dosage is less than the

required quantity, it reduces the workability and fluidity affecting the

fresh properties of SCC which in turn affects self compactability which

leads to reduction in strength. Whereas if the dosage of super

plasticizer is much higher than the required dosage, it increases

fluidity causing bleeding of SCC mix, thus affecting fresh properties of

SCC and in turn reducing the strength.

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8.6 INFLUENCE OF VISCOSITY-MODIFYING ADMIXTURE (VMA)

With the addition of viscosity-modifying admixture (VMA) in

SCC mixes, the viscosity enhances, which in turn reduces bleeding

and segregation of SCC. The fresh properties of self compacting

concrete mixes produced with mineral admixtures like GGBS and

RHA given in table 5.9 are within EFNARC limits.

The optimum dosage of VMA enhances the viscosity of fluid

mixture and reduces bleeding, segregation and settlement.

8.7 EVALUATION OF STRENGTH EFFICIENCY FACTORS

This study was mainly intended to evaluate the efficiency of

GGBS as admixture in Self Compacting Concrete mixes of grade M20,

M40 and M60 at 3, 7 and 28 days. The same parametric study is

carried out to find the efficiency of GGBS and RHA combination as

mineral admixtures in Self Compacting Concrete mixes of grade

M20,M40 and M60 at 3, 7 and 28 days .

Efficiency factors found from Bolomey‟s strength equation are

used to describe the effect of the GGBS and RHA combination

replacement in SCC in the enhancement of strength and durability

characteristics

8.7.1 Strength Efficiency factors “k” was calculated using a

modified version of the Bolomey equation, which is an empirical

relationship used to predict compressive strength of concrete. This

efficiency factor “k” of GGBS in SCC is the combination of two factors

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efficiency factor kg depending on the age of the concrete and the

efficiency factor kp depending on the various % of GGBS replacement

alone and also with other case of % GGBS and RHA in SCC.

Strength efficiency factor „k‟ increases by 21% in case of

GGBS+ RHA replacement in M20, M40 and M60 SCC mixes when

compared to the case of GGBS replacement alone in M20, M40 and

M60 SCC mixes, at 28 days.

When compared to M20, M40 and M60 grade SCC mixes

without any mineral admixture at 28 days, Strength efficiency of

GGBS increases by 31% in M20, 21% increase in M40 SCC mixes. In

M60 grade the required target strength was not reached when

replaced with GGBS, so 5% RHA is added to satisfy fresh properties of

SCC and also to obtain required target strength, then it is observed an

increase of 11% in M60 SCC mix.

Where as in case of GGBS RHA combination in SCC, the

Strength efficiency increases by 47 % in M20, 37% increase in M40

and an increase of 11% in M60 GGBS RHA SCC mixes when

compared to SCC mixes without any mineral admixture at 28 days at

optimum % GGBS and RHA replacement level.

8.8 STRESS-STRAIN BEHAVIOUR OF SCC WITH GGBS AND RHA

The stress-strain behavior of SCC mixes with and without steel

confinement is obtained by testing cylinders of standard size,150mm

diameter and 300 mm long in axial compression under strain control

as per IS 516-1959. Three cylinders for each mix are tested to study

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the stress-strain behavior. A total of one forty four cylinders are tested

in axial compression to get the stress-strain behavior of SCC mixes.

From the values of stresses and strains, average stress-strain curve

for each mix is plotted, taking the average values of the results of the

three cylinders.

The stress-strain values for eight SCC mixes with GGBS and

RHA, with and without steel confinement and the corresponding

stress-strain curves are shown in chapter V. The stress-strain values

of M20 are shown in tables 5.13.1 to 5.13.7, 5.15.1 to 5.15.7 and

5.17.1 to 5.17.7, whereas the curves are shown in figures 5.13.1 to

5.13.4, 5.15.1 to 5.15.4 and 5.17.1to 5.17.4 for M2S, M2SG and

M2SGR respectively.

The stress-strain values of M40 are shown in tables 5.19.1 to

5.19.7, 5.21.1 to 5.21.7 and 5.23.1 to 5.23.7 and the figures 5.19.1 to

5.19.4, 5.21.1 to 5.21.4 and 5.23.1 to 5.23.4 shows the curves of

M4S, M4SG and M4SGR respectively.

Similarly tables 5.25.1 to 5.25.7and 5.27.1 to 5.27.7 shows the

stress strain values of M60 and curves 5.25.1 to 5.25.4 and figures

5.27.1 to 5.27.4 shows the stress strain values of M6S and M6SGR

respectively.

8.8.1 Stress-Strain Response of SCC Mixes

From the observations made from stress-strain curves of all the

eight SCC mixes with GGBS and RHA with and without steel

confinement, the stress-strain pattern is observed to be almost

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similar. But in case of GGBS-RHA mixes there is improvement in

stress values. It is also observed that for higher grades of concrete,

with increase in stress there was decrease in strain.

8.8.2. Strains at Peak Stress on the Descending Portion of Stress-

Strain Curves of SCC

Compressive strain values corresponding to peak stresses of

M20, M40 and M60 mixes are observed and the average of peak strain

values for M 20 SCC is observed to be 0.0073, the peak strain value is

0.0067 for M 40 SCC and 0.0066 for M 60 SCC.

All values are more than compressive strain in conventional

concrete in axial compression, which is 0.002 as per IS 456-2000.This

indicates that the compressive strains at peak stress in steel confined

SCC is more than conventional concrete.

8.8.3 Normalized Stress-Strain Curves for SCC Mixes

From the stress-strain values of SCC mixes with and without steel

confinement and their corresponding stress-strain plots, normalized

stress-strain values are calculated by dividing each stress value by the

peak stress and dividing each strain value by strain at peak stress.

From the normalized stress-strain values of eight SCC mixes, the

average normalized stress-strain curves are plotted for M20, M40 and

M60 grades.

The normalized stress-strain values of M20 grade are shown in

tables 5.14.1 to 5.14.8, M20 GGBS are shown in 5.16.1 to 5.16.8 and

M20 GGBS-RHA are shown in 5.18.1 to 5.18.8. The relevant

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normalized stress-strain curves are shown in figures 5.14.1 to 5.14.8,

5.16.1 to 5.16.8 and 5.18.1 to 5.18.8.

The normalized stress-strain values of M40 grade are shown in

tables 5.20.1 to 5.20.8, M40 GGBS are shown in 5.22.1 to 5.22.8 and

M40 GGBS-RHA are shown in 5.24.1 to 5.24.8. The relevant

normalized stress-strain curves are shown in figures 5.20.1 to 5.20.8,

5.22.1 to 5.22.8 and 5.24.1 to 5.24.8 and the normalized stress-strain

values of M60 grade are shown in tables 5.26.1 to 5.26.8 and M 60

GGBS-RHA are shown in 5.28.1 to 5.28.8. The relevant normalized

stress-strain curves are shown in figures 5.26.1 to 5.26.8 and 5.28.1

to 5.28.8.

From the stress-strain curves of SCC mixes and average

normalized stress-strain curves, different parameters like energy

absorption capacity, peak stresses, strains and stress-strain behavior

are discussed.

Mathematical Models for Stress-Strain Curves of SCC Mixes.

Empirical equations for the stress-strain response of SCC mix have

been proposed in the form of Y =Ax/ (1+Bx2), where Y = σ/σ0 and

x = Є/Є0. The same empirical formula is valid for both ascending and

descending portions with different values of constants. A set of

constants A,B and A1,B1 have been determined to get empirical

equations for ascending and descending portions of normalized stress-

strain curves for different SCC mixes. The constants for mixes are

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Analytical Equations for SCC Mixes

The equations for ascending and descending portions of mixes are

Mix

Constants for ascending

portion

Constants for descending

portion

M20SCC mix A = 1.44, B = 0.53 A1 = 1.49, B1=0.71

M20 GGBS mix A = 1.53, B = 0.37 A1=2.0, B1= 1.20

M20 GGBS-RHA

mix A=1.20, B = 0.37 A1=1.29, B1=1.22

M40 SCC mix A=1.25, B = 0.58 A1=2.56, B1=1.77

M40 GGBS mix A=1.25, B = 0.27 A1=2.42, B1= 1.62

M40 GGBS-RHA

mix A=1.09, B = 0.22 A1=2.08, B1=1.30

M60 SCC mix A=1.41, B = 1.0 A1=2.27, B1=1.47

M60 GGBS-RHA

mix A=1.64, B = 0.33 A1=2.59, B1= 1.80

Mix

Equations for ascending

portion

Equations for descending

portion

M20SCC mix Y = 1.44 x/ (1+ 0.53 x2) Y = 1.49 x/ (1+0.71x2)

M20 GGBS mix Y = 1.53 x/ (1+0.37 x2) Y = 2.0 x/ (1+1.20 x2)

M20 GGBS-RHA

mix Y = 1.20 x/(1+0.37 x2) Y = 1.29 x/ (1+1.22 x2)

M40 SCC mix Y = 1.25 x/ (1+ 0.58 x2) Y = 2.56 x/ (1+1.77 x2)

M40 GGBS mix Y = 1.25 x / (1+0.27 x2) Y = 2.42 x/ (1+1.62 x2)

M40 GGBS-RHA

mix Y = 1.09 x/ (1+0.22 x2) Y = 2.08 x/ (1+1.30 x2)

M60 SCC mix Y =1.41 x/ (1+1.0 x2) Y = 2.27 x/ (1+1.47 x2)

M60 GGBS-RHA

mix

Y = 1.64 x/ (1+0.33 x2) Y = 2.59 x/ (1+1.80 x2)

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The proposed empirical equations can be used as stress block in

analyzing the flexural behavior of sections of SCC structural elements.

The proposed equations have shown good correlation with

experimental values.

8.8.4 INFLUENCE OF GGBS AND RHA.

The mixes designated as M2S, M4S and M6S are ordinary SCC

mixes whereas M2SG and M4SG contains mineral admixture GGBS

only and the mixes M2SGR, M4SGR and M6SGR contains mineral

admixture RHA in addition to GGBS. The remaining constituent

materials and their proportions in M2SGR , M4SGR and M6SGR are

same as in M2SG, M4SG and M6SG, hence comparison of results

M2SGR , M4SGR and M6SGR mixes is made with M2S,M2SG,M4S,

M4SG,M6S and M6SG mixes to study the influence of GGBS and

RHA on SCC mixes with regard to various parameters as follows.

8.8.5 Peak Stress

Peak stress values of the three SCC mixes are shown in tables

in chapter. Average Peak stress value is 35.30N/mm2 for M2S mix and

the average value for M2SG and M2SGR is 38.56N/mm2 and 41.23

N/mm2 respectively.

The average values for M4S, for M4SG and M4SGR mixes are

48.06N/mm2,50.04N/mm2 and 52.17N/mm2 respectively and the

average peak values are 63.42 N/mm2 and 65.66 N/mm2 for M6S and

M6SGR respectively. This indicates there is an increase in the peak

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compressive strength for different mixes blended with GGBS and RHA.

The increase may be due to high reactivity of RHA with GGBS.

8.8.5.1 Strain at Peak Stress

Peak compressive strain values corresponding to peak stresses of

M20 SCC mixes are shown in tables 5.13.8, 5.15.8 and 5.17.8,for M40

SCC mixes the values are shown tables 5.19.8, 5.21.8 and 5.23.8,for

M60 SCC mixes the values are shown in tables 5.25.8 and 5.27.8 .

Strain values corresponding to peak stress ranges from a

minimum of 0.00437 to a maximum of 0.00812 for M20 SCC mix,

0.00502 to a maximum of 0.00898 for M20 GGBS mix and 0. 00589

to 0.00934 for M20 GGBS-RHA SCC mix. Similarly the strain values

ranges from 0.00426 to 0.00728 for M40 mix, 0.005 to 0.00830 for

M40 GGBS mix, and 0.00574 to 0.009 for M40 GGBS-RHA mix. The

strain values of M60 ranges from 0.00414 to 0.00712, M60 GGBS-

RHA value ranges from 0.00529 TO 0.00836.

8.9 INFLUENCE OF STEEL

The eight mixes of SCC are confined with steel along with mineral

and chemical admixtures like GGBS, RHA, superplasticizers and

viscosity modifying agents. The cylinders are confined with different

percentage of steel i.e. 0%, 0.79%, 1.06%, 1.32%, 1.82%, 2.43%and

3.04%. Studies of results of three grades with different percentages of

steel for each mix are done separately. Comparisons are made among

SCC mixes with and without steel to study the influence of steel on

SCC mixes with regard to various parameters as follows.

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8.9.1. Peak Stress

Comparing the peak stress values of mixes with and without

steel an increase in the peak compressive stress of 6.56 % to 48.14%

is observed for M20 mixes, 7.29% to 18.66 % for M 40 mixes and 1.5%

to 11.33% for M60 mixes. The increase in stress is due to confinement

of steel. When the peak stresses of all the eight mixes are compared it

is observed that the there is drastic improvement in M20 and M40

mixes compared to M60 mixes. The observations are as follows

GGBS mixes

It observed that the increase is 7.64% to 48.88% for M20 GGBS

mix with different percentage of steel confinement when compared

with M20 GGBS mix without steel. Similarly when the stresses of M40

GGBS mixes with different percentages of steel are studied and

compared without steel, the observation is that the increase in average

values is 5.27% to 19.6% for M4S1 to M4S6 mixes.

GGBS-RHA mixes

When the values of GGBS-RHA mixes with steel confinement are

compared without steel confinement the increase in stress value is

8.14% to 41.6% for M 20 GGBS-RHA mix, 3.26% to 16.94% for M40

GGBS-RHA mix and 2.36% to 13.13% for M 60 GGBS-RHA mix. Thus

confinement of small percentage of steel to SCC mixes increases the

cylindrical strength marginally. Particularly the increase in stress is

observed in low and medium grades than higher grade of SCC for the

same strain levels and same percentage of steel confinement.

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Strains at Peak Stress on the Descending Portion of Stress-Strain

Curves

Compressive strain values corresponding to peak stress for the

eight SCC mixes are shown in tables. The average value of strain at

peak stress for M20 mix is 0.0073 which is almost four times the

maximum compressive strain at peak stress, i.e.0.002 for

conventional concrete in axial compression as per IS 456-2000. For

other two mixes also the values are almost three times to the standard

value. This indicates that the maximum compressive strain at peak

stress in SCC is with steel confinement. The steel present in cylinders

yielded for long time giving maximum strain.

8.10 TOUGHNESS OF SCC MIXES

Energy absorption capacity expressed in terms of area under

stress-strain diagram of SCC mixes is shown in table 5.39.1. The

average value of area under stress-strain diagram for M20, M40 &

M60 grade SCC mixes with different mineral and chemical admixtures

are observed to be 0.76 units, 0.78 units and 0.80 respectively.

Area under stress-strain curves are 0.66, 0.80 and 0.84 for M2S,

M2SG and M2SGR mixes respectively. Thus indicating an increase of

27% due to blending of RHA to SCC mixes. Area under M4S, M4SG

and M4SGR curves are 0.72, 0.74 & 0.90 respectively, indicating an

increase of 25%. Similarly area under M6S, M6SGR is 0.68 and 0.90,

indicating an increase of 36%.Thus RHA has considerable effect on

energy absorption capacity of SCC mixes. Thus blending of RHA with

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proper proportioning enhances the mechanical properties, peak stress

values, energy absorption capacity etc. of SCC mixes as long as the

fresh properties are within EFNARC specifications.

Ductility (µ) which indicates the deformable characteristic of

material is expressed as the ratio of strain in the descending to that in

the ascending portion of stress- strain curves. From the normalized

stress-strain curves, it is observed that there is improvement in

ductility due to the addition of GGBS and RHA to SCC mixes.

8.11 FLEXURAL BEHAVIOUR OF SCC BEAMS

Under and over-reinforced beams of size 100 x 150 x 1200 mm

with selected eight SCC mixes were cast, tested under two point

flexural bending tests under strain rate control. Beams were tested

until the load drops to about 15-20% of peak load in the descending

portion of load deflection curves. While testing the load at first crack,

ultimate load, curvature, crack width and crack pattern were observed

for all beams. Test set up is shown in plate no.1.10. The results are

shown in tables 5.40.1 & 5.40.2.

The following discussions are based on the experimental results

shown in tables 5.40.1 and 5.40.2, load-deflection and moment-

curvature plots shown in figures 5.41.1 to 5.41.3, 5.42.1 to 5.42.3

respectively.

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8.11.1. Load-Deflection Behaviour

Load-deflection plots for eight SCC mixes for under and over

reinforced beams are shown in figs 5.41.1 to 5.41.3.Up to application

of load at first crack the curve is linear and on further application of

load multiple cracks are caused and the deviation in curve is

observed.

For under reinforced beams with the increase in load the

multiple cracks increased. After the multiple cracking stages, it is

found that there is yield in steel so the P-δ curve become more or less

flat till the ultimate load is reached. On further increase in load a drop

in the load is observed with propagation of cracks. All the beams failed

by compression of concrete and the load deformation curves are

plotted up to failure stage. The same behavior was noticed in all the

under-reinforced SCC beams.

However in over-reinforced beams with flexural loading,

cracking was observed near the mid span of the beam. But, the

number of cracks formed is few when compared to under reinforced

beam. Crushing of concrete in compression was found beyond the

cracking stage. The strain values indicates that the steel

reinforcement is not fully stressed to its permissible value and hence

no yielding of steel has taken place, So the P-δ curves creep up till the

ultimate load is reached. The load deformation curves are plotted up

to failure stage, finally when all the beams failed by compression of

concrete. The behavior was same in all over-reinforced SCC beams.

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The differences noticed in the load deflection behavior of SCC

beams with and without GGBS and RHA are the increase in the

horizontal plateau of the load-deflection curve and the increase in load

at first crack and ultimate load in GGBS-RHA beams than that in SCC

beams.

8.11.2. Moment Curvature Relationship

Moment curvature plots for eight SCC mixes for under and over

reinforced beams are drawn and shown in figure 5.42.1 to 5.42.3.

These moment curvature plots for under and over reinforced beams

with GGBS and RHA observed to follow the similar pattern as that of

load deflection plots of beams.

In under reinforced beams with the increase in moment,

curvature increased gradually up to the multiple cracking stages and

beyond, and later curvature increased drastically at constant moment

or with small variation in the moment. The M-Ф curve is more or less

flat till the ultimate moment is reached. As all the beams failed by

compression of concrete the moment curvature plots are drawn up to

failure stage. The behaviour is similar in all the under-reinforced SCC

beams.

Whereas in over reinforced beams, after the multiple cracking

stage M-Ф curves creep up till the ultimate moment is reached. Finally

the beams failed by compression of concrete and the moment

curvature plots are drawn up to failure stage.

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The differences noticed in the moment-curvature behaviour of

SCC beams are, the increase in the horizontal plateau of the moment-

curvature plots and increase in ultimate moment in beams with GGBS

and RHA than that in ordinary SCC beams.

8.11.3. Load at First Crack

Both load at first crack occurred during the experiment and also

first crack load is determined from load-deflection plot corresponding

to the point on the curve at which the curve deviated from linearity is

observed. It is observed that the values obtained experimentally are

closer but higher than those values obtained from load deflection plots

of SCC beams.

Load at first crack increased with the addition of GGBS and

RHA which is due to the bond between the concrete and steel in

beams. As the GGBS and RHA are finer than cement the bondage is

more which arrests the micro cracks developed in the matrix which

results in requirement of more energy. This lead to an improvement in

load at first crack.

Load at first crack values for the under and over reinforced

beams made with eight SCC mixes viz M2S, M2SG, M2SGR… are

shown in tables 5.40.1 & 5.40.2. An increase in the load at first crack

by 10% to 5.5 % is observed due to an addition of GGBS in M20 and

M40 mixes and an increase of 35.00%, 14.18% and 15.56% due to

replacement of GGBS with 3% RHA in under-reinforced M20, M40

beams and with 5% addition of RHA in M60 beams.

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For over-reinforced beams, increase in load at first crack for

M20 mix is 22.6 % to 26.15% and for M40 mix an increase of 12.19%

to 16.58 % is observed. Similarly for M60 mix an increase of 15.61 %

is observed.

The increase is significant in both cases and it may be due to

high reactivity of RHA with GGBS. Also from the above results it is

observed that the dosage of RHA has yielded higher percentage

increase of load at first crack.

8.11.4. Ultimate Load

In under-reinforced beams after the multiple cracking stages,

the yielding of steel was found to be more, and ultimate load

corresponds to the yielding of steel and crushing of concrete. However

in over-reinforced beams steel reinforcement is not fully stressed to its

permissible value, ultimate load is due to crushing of concrete alone

and so due to compression failure of concrete the section failure

occurs.

When micro cracks develop in the matrix, the GGBS-RHA paste

present in the vicinity of such micro cracks will try to arrest these

cracks and prevent further propagation. Hence there is increase the

ultimate load, as the cracks that appear inside the matrix will take

meandering path, resulting in the demand for more energy for future

propagation. The GGBS-RHA beams have shown improved ultimate

load values compared to that of ordinary SCC beams.

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8.11.5. Deflections at Service Loads

The deflection at service load is determined from load deflection

plot corresponding to a load of Pu/1.5.Deflections observed from the

load-deflection curves for all the specimens at service loads(Pu/1.5)

are less than the maximum permissible deflection of 4mm i.e

span/250 specified by IS 456-2000. For under reinforced beams made

with GGBS and RHA, values of deflection at service load varied from

2.8- 4.0 mm and for over reinforced beams it varied from 2.2- 6.2 mm.

.

8.11.6 Crack Widths

The crack widths measured at ultimate load for under-

reinforced beams varied from 1.8 mm to 3.5 mm for SCC beams with

GGBS and RHA. For over-reinforced SCC beams the crack widths

varied from 1.5 mm to 3.0 mm

8.11.7 Crack Pattern

In under-reinforced SCC beams the visible flexural cracks

developed at 60% to 70% of the ultimate load of each beam and in

GGBS- RHA beams they developed at 75% to 85% of the ultimate load

of each beam. The crack started to widen considerably indicating

higher strains in steel than the yield strain in steel. All the beams

exhibited a tension failure which is a ductile failure. The cracks are

accompanied by pronounced bulging. When the load is further

increased, cracks propagated towards the top of the beam. As the

beams are forced to deform further, the cracks became more

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pronounced and the concrete crushed at one or both the ends. With

further increase in beam deflection, the load decreased, accompanied

by concrete spalling. This crack pattern is observed to be same for all

under-reinforced SCC beams, except the spacing of the cracks.

Similarly in all over-reinforced SCC beams failure is initiated by

spalling of concrete in the compression zone. At the time of occurrence

of spalling, the cracks propagated upto half to two third depth of the

beam. The load continued to increase slowly with the increase in

deflection. The beams failed by crushing of concrete. Crack pattern

indicates a compression failure in over reinforced beams. This crack

pattern is observed to be same for all over-reinforced SCC and beams,

except the spacing of the cracks. Crack pattern for beams are shown

in plates 1.11 and 1.12.

8.11.8 Maximum Deflection and Curvature at Failure

The maximum deflection values for under-reinforced SCC

beams varied from 19 to 38.50 mm. Where as for over-reinforced

beams these values varied from 7.71 to 16.28 mm. The higher values

of maximum deflection for under-reinforced beams are due to yielding

of reinforcement at ultimate loads. For over-reinforced beams, steel

does not yield at ultimate load hence there is reduction in the values

of maximum deflection.

Similarly the maximum curvature for under-reinforced SCC

beams varied from 113.42x10-6 to 83.95x10-6/mm. For over-reinforced

beams these values varied from 72.29 x10-6/mm to 37.08 x10-6/mm

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for SCC beams. Due to yielding of reinforcement at ultimate loads the

under-reinforced beams has shown higher values of maximum

curvature. For over-reinforced beams steel does not yield at ultimate

load, hence there is reduction in the values of maximum curvature.

8.11.9 Theoretical Moment-Curvature Values.

The values of experimental moments and curvatures are

calculated, from the loads and curvature meter readings obtained

from the beams tested under two point flexural bending tests under

strain rate control.

Theoretical moments and curvatures are calculated using the

analytical equations developed for stress-strain behaviour of SCC.

These equations were developed by conducting axial compression

tests on cylindrical specimens made with SCC. Using these equations

theoretical moments were calculated for SCC. Curvatures were

calculated from the strain distribution over the cross section. With

these values M-Ф curves were plotted. Theoretical moment curvature

values are shown in tables 5.45.1 to 5.45.8 and plots are shown in

figures 5.45.1 to 5.45.8.

Theoretical moment-curvature values of SCC with GGBS and

RHA mixes followed the same pattern as that of corresponding

experimental values. The only difference is that, the values of

theoretical moments calculated are lesser than the experimental

values for under-reinforced and for over reinforced beams.

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This may be because the curvature values in the experiment

were calculated over a specified gauge length but the theoretical

values at a section of the beam. Hence there is a difference between

experimental and theoretical values of curvatures.

8.11.10 Deflection at Service Loads

Deflections observed from the load-deflection curves (fig 5.41.1

to 5.41.3) of under and over reinforced specimens with out and with

RHA, at service loads (Pu/1.5) are less than the maximum permissible

deflection of 4.0 mm i.e. Span/250 specified by IS 456-2000.

Deflection at service loads is 4.0 mm to 2.8mm and for M2S,

M2SG and M2SGR respectively and M40 these values are 2.8 and 3.0

mm respectively and for M60 these values vary 2.9 to 3.2.Thus

blending of more dosage of RHA has reduced the deflection at service

loads and this may be because of high reactivity of RHA with GGBS,

thus increasing the strength and reducing the deflection at service

loads.

Load-Deflection Behaviour

Load-deflection plots for SCC mixes for under and over

reinforced beams with and without RHA are drawn and are shown in

figures 5.41.1 to 5.41.3. The load-deflection behavior is observed to be

similar for all under-reinforced SCC beams and all over-reinforced

SCC beams with and without RHA, except that the SCC mixes

containing RHA have shown an increase in load at first crack and

ultimate load compared to that of mixes without RHA.

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8.11.11 COMPARISON OF EXPERIMENTAL AND THEORETICAL

MOMENT-CURVATURE VALUES AND VALIDATION

The values of experimental moments and curvatures are

calculated from the loads and curvature meter readings obtained from

the beams tested under strain rate control. Theoretical moments and

curvatures are calculated using the analytical equations developed for

stress-strain behaviour of SCC. These equations were developed by

conducting axial compression tests on cylindrical specimens made

with SCC. Using these equations theoretical moments were developed

for SCC with GGBS and RHA. Curvatures were calculated from the

strain distribution over the cross section. With these values M-Ф

curves were plotted.

This difference in experimental and theoretical curvature values

is mainly due to the measurement of curvature over a short specified

gauge length during the experiment. Theoretically obtained curvature

represents the curvature at a section, where as the experimental

curvatures represent the curvature over a gauge length .Hence the

experimental curvature values are higher than the theoretical values.

Also the experiment was conducted beyond the ultimate stage

up to complete failure of the beam. At this stage the beams deflect by

large amounts before they fail. Hence there is a variation between

theoretical and experimental values of curvatures.

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8.12 DURABILITY STUDIES ON SCC

8.12.1 Durability factors

Acid Durability Factors The variation in ADF with different

percentages of GGBS and RHA replacement for M20, M40 and M60

grades are shown in Fig 7.1.1 to 7.1.9. Durability studies carried out

in the investigation through acid attack test with 5% H2SO4, 5% Hcl

and 5% Na2SO4 revealed that GGBS and RHA concrete are more

durable in terms of “Acid Durability Factors” than reference concrete.

The investigation through acid attack test with 5% H2SO4

revealed that rice husk ash concrete is 12% more durable in terms of

“Acid Durability Factors” than the reference concrete.

The investigation through acid attack test with 5% Na2SO4

revealed that rice husk ash concrete is 5% more durable in terms of

“Acid Durability Factors” than the reference concrete.

Durability studies carried out in the investigation through acid

attack test with 5% Hcl revealed that rice husk ash concrete is 16%

more durable in terms of “Acid Durability Factors” than the reference

concrete.

Acid Attack Factors

Fig. 7.1.1 to 7.1.9 shows the variation in ADF and AAF with

different percentages of GGBS and RHA replacement for M20, M40

and M60 grades.

Similar studies carried out in the investigation through acid

attack test with 5% H2SO4, 5% Hcl, 5% Na2SO4 revealed that GGBS

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and RHA concrete is less attacked for M20, M40 and M60 grades of

concrete in terms of “Acid Attack Factors” than the SCC concrete.

8.12.2 Weight loss

Figs. 7.2.1 to 7.2.9 show variation in percentage weight loss

with different percentages of GGBS and RHA replacement for M20,

M40 and M60 grades. It is observed that the percentage of weight loss

is more for the cubes immersed in 5% H2SO4, for SCC mix with GGBS

and RHA than ordinary SCC mixes.

8.12.3 Compressive Strengths

From the studies of compressive strengths for three grades of

concrete, before and after immersion in acids it is observed that when

immersed in Na2SO4 the three grades of SCC are showing lesser

compressive strength loss than immersed in H2SO4 and HCl.

The % compressive strength loss of M20 SCC mix, when

immersed in 5% H2SO4 is 1.3 to19.63 , For M20 SCC mix with GGBS

the % compressive strength loss values are 1.21 to 10.32, Similarly

the % compressive strength loss values for M20 GGBS-RHA SCC are

1.00 to 6.41 respectively.

From the studies of compressive strength, it is observed that the

compressive strength loss is more for cubes immersed in H2SO4 than

the cubes immersed in Na2SO4 and HCl.