an investigation on effects of fly ash on strength and ... · okamura and ozawa developed a mix...

177 Prof. Roshan Lal, Er. Kuldeep Kumar

An Investigation on Effects Of Fly Ash On Strength And

Flowability of Self Compacting Concrete

Prof. Roshan Lal Er. Kuldeep Kumar

PEC,University of Chandigarh College of

Technology Sector-12, Engg. and Technology,

Chandigarh Sector-26 Chandigarh

ABSTRACT : Self compacting concrete is able to flow under its own weight, completely filling formwork and achieving

full compaction even in the presence of congested reinforcement. Since the development of SCC, various investigations

have been carried out to standardize the proportioning of SCC mixes using different filler materials. The aim of present

study is to investigate the effects of variations in sand to aggregate ratio, super-plasticizer, VMA and replacement of

coarse aggregate by fine aggregate and cement by fly ash on flow-ability and strength characteristics of self compacting

concrete.

Keywords – SCC, Slump Flow Test, V-Funnel Test, L-Box Test, S/A Sand Aggregate Ratio, VMA (Viscosity

Modifying Agent), EFNARC, SP (Super-Plasticizer).

I INTRODUCTION

Concrete is the most basic material for any kind of construction work .The compacting of any conventional concrete is

done through external force using mechanical devices. Unlike the conventional concrete, self compacting concrete

doesn't require compacting using external force from mechanical equipments such as an immersion vibrator; instead SSC

is designed in such as way that it gets compacted under its own weight and characteristics. Once applied, the self

compacting property enables the concrete to fully spread around the reinforcement and completely fill the space within

the framework. The self compacting of concrete is achieved without losing any kind of strength, stability, or change in

properties. Self compacting concrete is a type of concrete, which is not a product of mixing substances having different

properties but a combination of several mixes having the same flow characteristics.

II. LITERATURE REVIEW

Okamura and Ozawa developed a mix design method in Japan in 1995, which is based on the characteristics of

materials used and their mix proportion. The course and fine aggregate contents are fixed while the water cementitious

ratio and super plasticizers content is adjusted to achieve self consolidation in the fresh concrete.

Typical steps involved are:-

i. The course aggregate content is fixed at 50% of solid volume of the concrete.

ii. The fine aggregate content is fixed at 40% of the mortar volume.

iii. W/C is assumed to be 0.9 – 1.0 % by volume depending on the binders.

iv. The super plasticizer dosage and final W/c ratio are determined to self consolidation.

Su, J. K. et al. studied the effect of sand ratio (fine aggregate volume/total aggregate volume) on the elastic

modulus of SCC. Various SCC mixes with differing S/A ratio were cast and tested. Elastic modulli were compared to

normal concrete. Authors concluded that the flowability increased with S/A ratio and elastic modulus of not significantly

affected by S/A ratio when total aggregate volume was kept constant.

Bauzoubaa N. et al.17

studied mixes of varying w/c ratio and fly ash content and presented the findings of fresh

and harden concrete properties. w/c ratio varied from 0.35 to 0.45 and flyash replacement was

varied from 40% to 60%. Slump test and V-funnel test were conducted to

measure flowability. The segregation test consist of gently pouring a 0.53 gallon (2 liter) container of fresh concrete over

a 0.2 in (5mm) mesh, and measuring the mass of the mortar passing the screen after 5 min was also performed. A stable


concrete should not pass more 5% segregation index. IN addition to this, breeding setting time and autogenous

temperature rise were also monitored.

ACI methods for grades from M20 to M40 and by Entropy and shack locks method for high strength concrete

of grades M45 to M60.

For SCC, to keep the powder content in between 160 and 240 litres/m3 fly ash is to be added in addition with

cement content obtained.

Coarse aggregates are replaced by fine aggregates and cement is replaced by fly ash simultaneously.

Some quality of cement is also replaced by fly ash. The fly ash replacement is varying from 5 to 20%.

After obtaining the quality of cement and fly ash for different grades, the optimum dosage of plasticizer for each

grade has been arrived by conducting Marsh Cone Test.

The total aggregate content obtained is distributed to the ratio 50:50 for sand and coarse aggregate.

The coarse aggregate content is reduced by adding fly ash as per second step.

The water content obtained is taken as it is and the check is to be made that the maximum water should not

exceed 210 litres/m3.

III EXPERIMENTAL PROGRAMME The objective of this programme is to obtain the properties of the different constituent materials to be used for making

the specimens for the experimental studies. The cement use for the experimental studies was Ultra-tech 43 grade

OPC.The various test performed on the cement and their values are shown in the Table 1. The results of the tests

performed on the fine aggregate such as fineness modulus and its physical properties are shown in Table 2 and 3

respectively. Coarse Aggregate used was a mixture of two available crushed stones of 10mm and 20mm size in 50:50

proportions. The sieve analysis and physical properties of coarse aggregate satisfied the requirement of IS: 383-1970 and

the results are given in table 4 and table 5 respectively. To assess the properties of fly ash, results were obtained from

laboratory tests conducted by Central Soil and Material Research Station (CSMRS), New Delhi and CBRI-Roorkee were

considered for exploiting its suitability for making self compacting concrete. Chemical and index properties of fly ash are

listed in table 6 and 7.The water used in the concreting work was the potable water as supplied in P.G. structure

laboratory of our institute. Water used for mixing and curing was clean and free from injurious amounts of oils, acids,

alkalis, salts and sugar, organic materials or other substances that may be deleterious to concrete. As per IS 456:2000

portable water is generally considered satisfactory for mixing and curing of concrete. Accordingly portable tap water was

used for preparation of all concrete specimens.

Table 1: Characteristics Properties of Cement Table 2: Sieve Analysis of Fine Aggregate

Total Weight of Sand taken= 1000gm

Fineness Modulus of fine sand = 3.17

IS Sieve Wt.

Retained

on sieve

(gm)

Cumulative

%age

retained

%age

passing

4.75mm 10.1 1.01 98.99

2.36mm 23 3.31 96.69

1.18mm 100.6 13.37 86.63

600µ 143.9 27.76 72.24

300µ 493.1 77.07 22.93

150µ 176.6 94.73 5.27

Pan

52.2 99.95 0.05

Sr.No Characteristics Results

1 %Consistency of cement 30

2 Specific gravity 3.14

3 Initial setting time (minutes) 55

4 Final setting time (minutes) 380

5 Compressive strength

(N/mm2)

(i) 3 days

(ii) 7 days

(iii)28days

24.10

34.12

53.54

34.56

47.92

6 Soundness (mm) 1.00

7 Fineness of Cement (gm) 0.50


Table 3: Physical Properties of Fine Aggregate Table 5: Physical properties of Coarse aggregate

Table 4 : Fineness Modulus of Proportioned Coarse Aggregates

IS sieve

designation

Wt. Retained on

sieve 20 mm agg.

(gm)

Wt. Retained on

sieve 10 mm agg.

(gm)

Total Wt.

Retained

(gm)

Percentage Wt.

Retained

Percentage

Passing

80 mm 0.00 0.00 0.00 0.00 100.00

40 mm 0.00 0.00 0.00 0.00 100.00

20 mm 0.00 0.00 0.00 0.00 100.00

10 mm 2246.90 1159.70 3406.60 68.13 31.87

4.75 mm 249.35 1003.45 1252.80 93.19 6.81

Pan (<4.75) 3.75 336.85 340.60 - -

Total Wt. 2500 2500 5000 ∑C = 161.32

Total weight of 10mm aggregate = 5000gm

Fineness modulus = ∑C+500/100 = 161.32+500/100 = 6.6132

Table 6: Chemical Properties of Fly Ash Table 7: Index Properties of Fly Ash

Superplasticizer “CICO super plast HS” procured from CICO Tech. Ltd. Gurgoan was used in the present study. Its

dark brown in color. CICO super plast HS is especially suitable for the production of concrete mixes which require high

early strength development, powerful water reduction and excellent flow ability. It is mainly used for the following

applications: Precast concrete, fast track concrete, in situ concrete requiring fast stripping time, self compacting concrete

(SCC). The viscosity modifying admixture “CICO plast super” procured from CICO Tech. Ltd. Gurgoan was used in

the present study. Its pale yellow in color. CICO plast super is a universal concrete admixture to improve difficult

concrete mixes and to protect concrete pumps and pipes from excessive material wear.

MIX DESIGN

The mix taken for investigation is M25, the proportions of initial trial mixes TR1, TR2 and T1 are shown in Table 8.

Property Result

Specific Gravity of Fine

Aggregates

2.62

Free Moisture Content 2%

Water Absorption 1.60%

Characteristics Test values of

obtained Color Grey

Shape Angular

Type Crushed

Maximum size 10 mm

Specific gravity 2.66

Fineness modulus 6.61

Properties Values

Colour Dark Grey

Class F

Specific gravity 2.05

Surface Area in cm2/gm 4680

Lime Reactivity in kg/ cm2 59.80

Bulk Density in kg/ m3 1000

Compressive strength as % of

corresponding (P.C.C.)

90.95

Characteristics Results

% Loss on ignition 4.52

Silica (SiO2) 56.32

Alumina (Al2O3) 30.87

Iron Oxide (Fe2O2) 4.94

Calcium Oxide (CaO) 1.58

Magnesium Oxide (MgO) 0.70


Table 8: Proportions of TR1, TR2 and T1

Trial mix Water

(lt/m3)

Cement (kg/m3) Fine Aggregates

(kg/m3)

Coarse Aggregates

(kg/m3) TR1 191.58 416.478 523.285 1189.32

TR2 191.58 420.00 556.32 1179.1

T1 191.58 425.00 599.13 1163.02

The mix TR1 and TR2 were not cohesive, so another mix T1 was designed.

Further modifications and variations in mix T1 were made to meet strength and other performance requirements as per

the following guidelines:

Water/Powder ratio by volume 0.80 to 1.10.

Total Powder Content – 160 to 240 liters (400-600kg) per cubic meter.

Coarse aggregate content normally 28% to 35% by volume of the Mix.

Water cement ratio is selected based on requirements in EN 206.

Typically water content was kept upto 215 litres / m3.

The sand content balance the volume of other constituents.

The trial mixes with and without fly ash are shown in table 9 and 10 were prepared to fulfill the requirements of SCC i.e.

filling ability, passing ability and segregation resistance. Table 9: Mix Proportions for SCC

S.No Mix Cement

Kg/m3

F.A.

Kg/m3

C.A. kg/m3

Fly Ash Water

Kg/m3

S.P.

%

V.M.A

%

S/A

ratio

1 T1 425 599.13 1163.02 - 191.58 - - 0.34

2 T2 425 634.38 1127.78 - 194.58 - - 0.36

3 T3 425 651.99 1110.17 - 199.58 - - 0.37

4 T4 425 704.86 1057.29 - 203.58 - - 0.40

5 T5 425 775.35 986.81 - 207.58 1.0 - 0.44

6 T6 425 810.59 951.57 - 210.58 1.0 - 0.46

7 T7 425 916.81 845.83 - 215.58 1.1 - 0.52

8 T8 425 986.81 775.35 - 215.58 1.1 - 0.56

9 T9 425 1022.05 740.11 - 215.58 1.2 0.1 0.58

10 T10 425 1039.67 722.49 - 215.58 1.2 0.2 0.59

11 T11 425 1039.67 722.49 - 215.58 1.3 0.3 0.59

12 M0 425 1039.67 722.49 - 215.58 1.3 0.4 0.59

Table 10: Mix Proportions for SCC Containing Fly Ash

S.No Mix Cement

kg/m3

F.A.

kg/m3

C.A.

Kg/m3

Fly Ash Water

Kg/m3

S.P.

%

V.M.A

%

S/A

ratio

1 M1 382.5 1111.92 650.24 42.5 215.58 1.3 0.4 0.59

2 M2 340.0 1184.17 577.99 85.0 215.58 1.3 0.4 0.59

3 M3 297.5 1256.42 505.74 127.5 215.58 1.3 0.4 0.59

Where,

T1- control mix in which S/A = 0.34%, w/c = 0.450, T2- S/A = 0.36%, w/c = 0.457

T3- S/A = 0.37%, w/c = 0.469, T4- S/A = 0.40%, w/c = 0.479

T5- S/A = 0.44%, w/c = 0.488, SP = 1%, T6- S/A = 0.46%, SP = 1%

T7- S/A = 0.52%, SP = 1.1%, T8- S/A = 0.56%, SP = 1.1%


T9- S/A = 0.58%, SP = 1.2%, VMA = 0.1%

T10- S/A = 0.59%, SP = 1.2%, VMA = 0.2%

T11- S/A = 0.59%, SP = 1.3%, VMA = 0.3%

M0- S/A = 0.59%, SP = 1.3%, VMA = 0.4%

M1- 10% replacement of Cement by Fly Ash and Coarse Aggregates by Fine Aggregates both simultaneously.

M2- 20% replacement of Cement by Fly Ash and Coarse Aggregates by Fine Aggregates both simultaneously.

M3- 30% replacement cement by Fly Ash and Coarse Aggregates by Fine Aggregates both simultaneously.

IV DISCUSSION OF RESULTS Various concrete mixes were tested to determine the SCC properties as per the EFNARC guidelines for SCC. Slump

flow test for filling ability, V-funnel for filling and segregation resistance and L-box test to determine passing ability

were conducted on each mix and the mix was modified after making observations of previous mix behavior. The results

of various tests on fresh concrete mixes are reported in table 11.

Table 11: Workability Results

S.No Mix Slump flow V-funnel

Tf (sec)

V-funnel

T5 (sec)

L-box

(H2 / H1)

1 T1 300 - - -

2 T2 325 - - -

3 T3 340 - - -

4 T4 400 - - -

5 T5 445 58 61 -

6 T6 510 45 57 0.59

7 T7 660 30 40 0.72

8 T8 790 20 31 0.86

9 T9 760 18 22 1.08

10 T10 720 12.1 18.9 1.02

11 T11 700 10.2 16.2 0.99

12 M0 695 11.9 14.7 0.94

13 M1 685 12.4 15.2 0.90

14 M2 670 13.2 16.0 0.84

15 M3 650 14.9 18.0 0.80

Slump flow

The measurement of slump flow for a typical mix is shown in plate 1 .The slump flow value for trail mix T1 is much

below the required flow of 650mm -800mm as per EFNARC guidelines. In trial mix T2 the slump flow value increased

to 325mm.

Further simultaneous increase in sand to aggregate ratio and water cement ratio resulted in further increase in slump

flow value. However, the slump flow value required as per EFNARC guidelines was not obtained. Therefore in mix T5,

sand to aggregate ratio was increased to 0.44 and water cement ratio was increased to 0.49 and 1.0% of super-plasticizer

by weight of the cement was introduced in the mix. The increased S/A ratio and introduction of super-plasticizer resulted

in further increase in the flow to 445mm. The further increase in S/A to 0.46 in mix T6, with water cement ratio of 0.49

and super-plasticizer of 1.0% resulted in increase in slump flow value to 510mm. The increase in slump flow with

increase in sand to aggregate ratio may be attributed to partial replacement of coarse aggregate by sand which improves

flow-ability property of concrete and also holds all the constituents together.

In trial mix T7 and T8 dosage of super plasticizer was kept as 1.1%, but S/A ratio was further increased to 0.52%

and 0.56% respectively, which resulted in further increase in the slump value to 660 mm to 790 mm respectively. But

this mix showed signs of segregation and bleeding. To overcome these problems 0.1% of viscosity modifying admixture

(V.M.A.) was introduced in mix T9. With the addition of V.M.A in trial mix T9, the mix became cohesive and

homogeneous. However, the slump value decreased to 760 mm.


In trial mixes M1, M2 and M3 the SP and V.M.A were kept constant and the coarse aggregates were replaced by

sand and Cement was replaced by fly ash simultaneously by 10%, 20% and 30% respectively. The replacement of coarse

aggregate by sand and cement by fly ash resulted in decrease in slump flow values. The slump flow values for M1, M2

and M3 were obtained as 685 mm, 670 mm and 650 mm respectively which are lower than the value obtained for mix

M0 (mix without fly ash) but were within the ranges as per EFNARC guidelines.

From the above discussion it is clear that the simultaneous increase in S/A ratio and dose of SP results in increased

slump flow value. The increase in slump due to increase in SP percentages is attributed to the dispersion action of super

plasticizer in the concrete mix. It can further be seen from table 11 that the slump value decreased with increase V.M.A.

in the mix. This is due to the fact that V.M.A. makes concrete more homogeneous but reduces the free flow of concrete.

It can also be seen from figure 1 that simultaneous replacement of cement by fly ash and coarse aggregate by sand

resulted in decreased slump flow value of the mix. This is due to the fact that with the replacement of coarse aggregate by

sand and cement by fly ash, the increased fineness in the mix comes into picture which results in increased water

demand.

Plate 1: Slump Flow Test Fig.1: Variation of Slump Flow Test Results

V-Funnel test

The nature of the test and flow is shown in plate no 2 for a typical mix. It can be seen from table 11 and figure 2

that mixes T1, T2, T3 and T4 were not able to pass through V-funnel fully. Only some part of concrete could pass.

Therefore, in mix T5 sand to aggregate ratio was increased to 0.44 and water-cement ratio was increased to 0.49 and

1.0% of super-plasticizer of the weight cement was induced in the mix. The increased S/A ratio and introduction of

super-plasticizer made the mix flow-able which passed through and the value of V- Funnel was recorded 58 seconds. The

further increase in S/A ratio to 0.46 in mix T6, with water cement ratio of 0.49 resulted in decrease in V-funnel to 45

seconds. In trial mix T7, dosage of super plasticizer was increased to 1.1% and S/A ratio was increased to 0.52, which

resulted in further decrease in the passing time to 30 seconds. Further increase in S/A ratio to 0.56 and dosage of super-

plasticizer to 1.1%, resulted in further decrease in value to 20 seconds. This mix showed signs of segregation and

bleeding. To overcome these problems 0.1% of V.M.A. was introduced in mix T9 and the super-plasticizer was increased

to 1.2% and S/A ratio was increased to 0.58. With the addition of V.M.A. in trial mix T9, the mix became homogeneous

which resulted in the increase in the passing time to 18 seconds. Further in mix T10 with S/A ratio as 0.59, dosage of

super plasticizer as 1.2% and with increased dosage of V.M.A. of 0.2%, value of V-funnel increased to 12.1 seconds.

In trial mix T11, S/A ratio was kept as 0.59, the dosage of super plasticizer and V.M.A. were increased to 1.3% and

0.3% respectively, the V-funnel value for this mix increased to 10.2 seconds. Further in control mix M0, S/A ratio was

kept as 0.59 and super plasticizer dosage as 1.3% and dosage of V.M.A. was increased to 0.4%, the V- Funnel value for

this mix increased to 11.9 seconds. In trial mixes M1, M2 and M3, SP and V.M.A. were kept constant and the coarse

aggregates were replaced by fine aggregates and cement by fly ash simultaneously by 10%, 20% and 30% respectively.

The replacement of coarse aggregate by fine aggregates and cement by fly ash resulted in increase in the passing time of

V-funnel. The passing time for V-funnel for M1, M2 and M3 were recorded as 12.4 seconds, 13.2 seconds and 14.9

seconds respectively, which are higher than the time recorded for mix M0 (mix without fly ash). However, the values of

the mixes M1, M2 and M3 were within the range per EFNARC guidelines.

It is clear from the above discussion that the increase in S/A ratio and super plasticizer dosage resulted in decrease in

the passing time of the V- funnel. The decrease in the passing of V-funnel time due to increase in S/A ratio is due to the


minimization of the friction between the coarse aggregates. The addition of super plasticizer decreased the passing time

of V-funnel due to its dispersing action as already discussed in the slump flow.

V-Funnel Test at T 5min

V (T5min) Funnel test is used to determine the segregation resistance of the concrete. In this test bottom lid of

apparatus is opened after period of 5 minutes. The nature of the test and flow is shown in plate no 3 for a typical mix.

The results obtained from V (T5min) Funnel test for various mixes presented in the table 11 it clearly show that

concrete mixes T1, T2, T3 and T4 were not able to pass through V-funnel. Time interval (5min) between filling of

apparatus and opening of bottom lid make coarse aggregate to settle and blockage was occurred. Therefore in mix T5

sand to aggregate ratio was increased to 0.44 and water cement ratio was increased to 0.49 and 1.0% of super-plasticizer

of weight of cement was introduced in the mix. The increased S/A ratio and introduction of super plasticizer resulted in

improvement in flow through V-funnel and value was obtained as 61 seconds. In the mix T6, the dosage of super

plasticizer was kept constant and same as 1.0% but the S/A ratio was changed to 0.46 in trial mix, which resulted in the

decrease in the passing time to 57 seconds. In trial mix T7, dosage of super plasticizer was increased to 1.1% S/A ratio

was increased 0.52, which resulted in further decrease in the passing time to 40 seconds. Further increase in S/A ratio to

0.56 and dosage of super-plasticizer as 1.1% resulted in further decrease in the value to 31 seconds. Viscosity modifying

Agent (V.M.A.) was introduced in trial mix T9 and the super-plasticizer was increased to 1.2% and S/A ratio was

increased to 0.58, with addition of V.M.A. in the trial mix T9, the mix became cohesive, however the passing time of V-

funnel decreased to 22 seconds. Further in trial mix T10 with S/A ratio as 0.59, dosage of super-plasticizer as 1.2% and

with increased dosage of V.M.A. of 0.2%, value decreased to 18.9 seconds. In trial mix T11, S/A ratio was kept as 0.59,

the dosage of super plasticizer and V.M.A. as 1.3% and 0.3% respectively, the value for this mix increased to 16.2

seconds. Further in control mix M0, S/A ratio was kept as 0.59 and super plasticizer dosage as 1.3% and dosage of

V.M.A. was increased to 0.4%, the value further increased to 14.7 seconds.

In trail mixes M1, M2and M3 S/A ratio, SP and V.M.A. were kept constant and the coarse aggregates were replaced

cby fine aggregates and cement by fly ash simultaneously by 10%, 20% and 30% respectively. The replacement of coarse

Aggregate by fine aggregates and cement by fly ash simultaneously resulted in increases in passing time to 15.2 seconds,

16.0 seconds and 18.0 seconds respectively. However, the values of the mixes M1, M2 and M3 were within the range as

per EFNARC guidelines.

It is clear from the above discussion that the increased S/A ratio and super-plasticizer dosage result in decrease in the

passing time of the V-Funnel. T5 minutes, the trend being similar to the trend observed for V- funnel test.

Plate 2: V-Funnel test Plate 3: V-Funnel at T5min

Fig.2: Variation of V-funnel Test Results (time)


L-Box Test This test determines the flow of the concrete, and the extent to which it is subjected to blocking by reinforcement.

This test indicates the one dimensional flow-ability of the mix in restrained conditions. This test also useful in both ways

as blocking and lack of stability can be detected visually. The size of opening and its relative distance from the concrete

could be varied to obtain a better understanding of the potential for blocking at a lower velocity of flow. The nature of the

test and flow of concrete in L-box is shown in plate no 4 for a typical mix.

The results of L-Box test are presented in table 11 clearly show that concrete mixes T1, T2, T3 and T4 were not able

to pass through L-Box. Therefore, in mix T5, S/A ratio was increased to 0.44 and w/c ratio was increased to 0.49 and

1.0% super-plasticizer of the weight of cement was induced in the mix. The increased S/A ratio and introduction of

super- plasticizer made the mix flow-able which passed through L-box and the value was recorded as 0.52. Further

increase in S/A ratio to 0.46 in mix T6, with w/c ratio of 0.49 the blocking ratio improved to 0.59. In trial mix T7, dosage

of super-plasticizer was increased to 1.1%, S/A ratio was kept as 0.52, which resulted in the increased blocking value of

0.72. Further increase in S/A ratio to 0.56 and dosage of super plasticizer to 1.1%, resulted in further increase in blocking

ratio to 0.86. When V.M.A. was introduced in T9, the mix became more cohesive, which resulted in the increase in the

blocking ratio to 1.08.

Further in trial mix T10 with S/A ratio as 0.59, dosage of super plasticizer as 1.2% and with increased dosage of

V.M.A. of 0.2%, value of blocking ratio for this mix decreased to 1.02.

In trial mixes T11, S/A ratio was kept as 0.59, super plasticizer dosage as 1.3% and dosage of V.M.A of 0.4%, the

blocking value further decreased to 0.99. Further in control mix M0, S/A ratio was kept as 0.59 and super plasticizer

dosage as 1.3% and dosage of V.M.A. of 0.4%, the blocking value for this mix decreased to 0.94.

In trial mixes M1, M2 and M3, SP and V.M.A. were kept constant and the coarse aggregates were replaced by fine

aggregates and cement by fly ash simultaneously by 10%, 20% and 30% respectively. The replacement of coarse

aggregate by fine aggregates and cement by fly ash simultaneously resulted in decrease in the blocking ratio of the L-box

test. The blocking ratio test for M1, M2 and M3 were recorded as 0.90, 0.84 and 0.80 respectively, which are within the

range as per the EFNARC guidelines for self compacting concrete.

It can be clearly seen from the above discussion that with the increase in the dosage of super-plasticizer with

simultaneous increase in S/A ratio and Water Cement ratio, the blocking ratio increased. Again, with the addition of

VMA, blocking factor first increased then it decreased. This is due to the fact that VMA modifies the viscosity of

concrete and reduces the segregation tendency but further addition of V.M.A. decreases the filling ability as well as the

passing ability of the concrete mix.

Plate 4: L-Box Test Fig.3: Variation of L-box Test Results

COMPRESSIVE STRENGTH

The effect of replacement of coarse aggregates by fine aggregates and cement by fly ash on compressive strength of

SCC was investigated and has been discussed in the following sections.

Effect of Fly Ash on Compressive Strength of SCC

The results of compressive strength tests using fly ash in varying percentages (i.e. 0%, 10%, 20% and 30%) as partial

replacement of cement at moist curing ages of 7 and 28 days are presented in table 12 and figures 4 and 5 which show the

variation of compressive strength of SCC with different replacement levels of fly ash at various ages of moist curing.


Table 12: Variation of Compressive Strength for different Replacement

Levels of Fly Ash (N/mm2)

Mix design % replacement by fly ash Duration of moist curing (days)

7 28

M0 0 27.32 35.11

M1 10 26.00 34.08

M2 20 24.45 33.59

M3 30 22.83 32.03

Fig 4: Variation of Compressive Strength for Fig 5: Variation of Compressive Strength Vs

Different Replacement Levels of Fly Ash (N/mm2) Duration of Moist Curing for 7Days and 28 Days.

It is clear from the above table 12 and figure 4 and 5 that the compressive strength of SCC mix (M1) with 10%

replacement of coarse aggregates by fine aggregates and cement by fly ash is almost comparable to SCC mix without any

replacement. However, the compressive strength for mixes M2 and M3 decreased with increase in percentages of

replacement of cement by fly ash and coarse aggregates by fine aggregates. The compressive strength of SCC with fly

ash is lower due to the reason that reduction in quantity of cement by replacement with fly ash, results in weakening the

cohesion of the cement paste and adhesion to the aggregate particles.

SPLIT TENSILE STRENGTH The results of split tensile strength tests using fly ash in varying percentages (i.e. 0%, 10%, 20% and 30%) as partial

replacement of cement the moist curing ages of 7 and 28 days are presented in table 13.

Table 13: Variation of Split Tensile Strength for different Replacement Levels of Fly Ash (N/mm2)

Mix design % replacement of fly ash Duration of moist curing

(days) 7 28

M0 0 3.25 4.58

M1 10 2.96 4.11

M2 20 2.77 3.85

M3 30 2.56 3.43

The variation of split tensile strength of SCC with different replacement levels of fly ash at various ages of moist curing.

The test result is shown in figure 6 and 7.


Fig 6: Graphical Representation of Variation of Fig 7: Graphical Representation of Variation of

Split Tensile Strength for different Replacement Split Tensile Strength Vs Duration of Moist Curing

Levels of Fly Ash (N/mm2) at 7 Days and 28 Days

It is clear from the above table 13 and figure 6 and 7 that the split tensile strength of SCC containing fly ash are lower

than of control mix (M0).The tensile strength decreased with replacement of cement by fly ash content. The tensile

strength of SCC mixes containing fly ash is also less than that of SCC without fly ash for all replacement levels, reason

for that is same as already explained in case of compressive strength. The control mix achieved strength of 3.82MPa at

the age of 28 days while the SCC containing fly ash with cement replacement levels of 10%, 20% and 30% attained

strength of 3.54MPa, 3.44MPa and 3.05MPa respectively. Thus the fly ash concrete with 10%, 20% and 30%

replacement of cement gained 0.93, 0.90 and 0.80 times strength in comparison to the control mix at the age of 28 days

respectively. VI CONCLUSIONS

On the basis of results obtained in this study, the following conclusions can be drawn:

i. The increase in w/c ratio and sand to aggregate ratio (S/A) results in improvement in the slump flow of SCC. When

S/A ratio was increased from 0.34 to 0.36 and the w/c ratio was increased from 0.450 to 0.457 in trial mix T2 from

T1, the slump flow was increased by 10.83%. With further increase in water cement ratio from 0.457 to 0.469,

keeping the S/A ratio constant as 0.37 the slump flow value further increased to 340mm in trial mix T3. Further

increase in S/A ratio and water cement ratio to 0.40 and 0.44 respectively in mix T4 resulted in further increased in

slump flow. The slump flow value for mix T5 was obtained as 445mm which is 11.125% higher that the slump flow

value obtained for mix T3. Further increase in w/c ratio, at 0.40 S/A ratio (mix T4), resulted in further improvement

in slump flow value. Again when w/c ratio and S/A ratio were increased to 0.495 and 0.46 respectively in mix T6,

the slump flow value increased to 510 mm, which is 11.46% higher than slump flow value obtained for trial mix T6.

ii. Simultaneous increase in S/A ratio and super-plasticizer results in improvement in the filling ability of the self

compacting concrete. The addition of 1.0% super-plasticizer in the trial mix T5 with w/c ratio of 0.488 and S/A ratio

of 0.44, the slump flow increased to 445mm, which is 11.125% higher than the slump flow obtained for trial mix

T4. With further increase in S/A ratio to 0.46 and super-plasticizer dosage of 1.0% the slump flow further increased

to 510mm, in trial mix T6. When super-plasticizer was further increased to 1.1% in trial mix T7 with S/A ratio of

0.52, the slump flow increased to 660mm. In trial mix T8 dosage of super-plasticizer was kept as 1.1% same as T7,

with S/A ratio of 0.56, the slump flow increased to 790mm. In trial mix T9 S/A ratio was kept as 0.58 and with

super-plasticizer dosage was increased to 1.2%, the slump flow for this mix increased to 760mm. The addition of

viscosity modifying agent results in reducing the segregation and bleeding in the mix, however, the slump flow

value is decreased with addition of V.M.A. With further increase in S/A ratio to 0.59 and with super-plasticizer

dosage of 1.2 % and with 0.2% addition of viscosity modifying agent the slump flow value decreased to 720 mm in

trial mix T10. In trial mix T11 the S/A ratio was constant as 0.59, with the increase in superplasticizer dosage of

1.3% and viscosity modifying agent of 0.3% , the slump flow value decreased to 700mm.

iii. The simultaneous replacement of cement by fly ash and coarse aggregates by fine aggregates resulted in decrease in

slump flow values for all replacement levels i.e. 0%, 10%, 20% and 30%. In mix M0, M1, M2 and M3, S/A ratio

was kept constant as 0.59 , superplasticizer and VMA were kept constant as 1.3% and 0.4% respectively , the slump

flow for these mixes were recorded as 695 mm, 685 mm, 670 mm and 650 mm respectively.


iv. The simultaneous increase in S/A ratio, water content, super-plasticizer and VMA resulted in decrease in V-funnel

time. But the replacement of cement by fly ash and coarse aggregates by fine aggregates resulted in increase in V-

funnel time. V-funnel time recorded for mix T9 with S/A ratio of 0.58, SP dosage of 1.0 and VMA content of 0.1%

was 11.2 seconds. V-funnel decreased to 10.2 seconds when the S/A ratio, super-plasticizer and VMA content were

increased to 0.59, 1.3% and 0.4% respectively in mix M0.

v. The simultaneous replacement of cement by fly ash and coarse aggregates by sand resulted in decrease in V-funnel

time. In mix M0, M1, M2 and M3, S/A ratio was kept constant as 0.59, superplasticizer and VMA were kept

constant as 1.3% and 0.4% respectively, the V-funnel for these mixes were recorded as 11.9, 12.4, 13.2 and 14.9

respectively.

vi. The increase in S/A ratio and superplasticizer resulted in increase in blocking factor values. The addition of VMA

also improves the blocking factor value, however, the blocking factor value decrease at higher dosages of VMA.

The simultaneous replacement of cement by fly ash and coarse aggregate by sand, resulted in further decrease in

blocking factor values for all replacement levels. The blocking factor values of 0.90, 0.84 and 0.80 were obtained

for fly ash mixes M1, M2 and M3 respectively, while the blocking factor for mix without fly ash i.e. M0 was

observed to be 0.94.

vii. Partial replacements of coarse aggregate by fine aggregate and cement by fly ash in SCC mixes resulted in decrease

in compressive strength and split tensile strength. However the percentage in strength is less at 28 days as compared

to 7 days.

REFERENCES

1. IS 516:1959 (reaffirmed 1999); Methods of tests for strength of Concrete, Bureau of Indian Standards, New Delhi. 1997.

2. IS 5816:1970 Method of test for split tensile strength of concrete cylinders.

3. IS 2269:1982, specifications for ordinary Portland cement, bureau of Indian standards, New Delhi.

4. IS 10262:1982 Recommended guidelines for concrete mix design, Bureau of Indian Standards, New Delhi.

5. Japanese Architectural Society: "Specification for reinforced concrete work", Tokyo 1986.

6. IS: 8112-1989. "Specifications for Ordinary Portland Cement 43 grade". Bureau of Indian Standards, New Delhi. 1989. 7. IS 8112-1989. “specifications for coarse and fine aggregates from natural sources.” Bureau of Indian standards, New Delhi. 1997.

8. Okamura, H., "Self-Compacting High Performance Concrete," ACI Concrete International, Vol. 19, No. 7, July 1997, pp. 50-54.

9. H. Okamura, et al., "High Performance Concrete", Gihoudou Pub, Tokyo, 1993 (In Japanese). 10. JRMCA, "Manual of Producing High Fluidity (Self-Compacting) Concrete", JRMCA, Tokyo, 1998.

11. Japanese Society of Civil Engineering, "Guide to Construction of High Flowing Concrete.", Gihoudou pub, Tokyo, 1998.

12. IS: 5816-1999, “ Method of test for splitting tensile strength of concrete cylinders,” Bureau of Indian standards, New Delhi. 13. IS 456:2000 “ Indian standard code of practice for plain and reinforced concrete” (4th revision), Bureau of Indian standards, New Delhi.

14. Su, J. K., et al, "Effect of sand ratio on the elastic modulus of SCC", Journal of marine Science and technology, Vol. 10, No.1, 8-13, 2002.

15. Bouzoubaa N. and Lacheni M., “Self Compacting Concrete and High Volumes of Class F fly ash, preliminary result,” cement and concrete research, Vol. 31, No. 3 March 2001, pp 413-420.

16. Specifications and guidelines for self compacting concrete, EFNARC, Hemisphere, U.K. February 2002.

25. EFNARC specifications & guidelines for self-compacting concrete 2002. . 17. “Self–Consolidating Concrete”, ACI Materials Journal, September 2006, V. 103, pp. 374-383.

18. The National Building code of India, Bureau of Indian standards, New Delhi.

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