Strength and Workability

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STRENGTH AND WORKABILITY

CHARACTERISTICS OF FLY ASH

BASED GLASS FIBRE REINFORCED

HIGH-PERFORMANCE-CONCRETE

Dr.H.Sudarsana Rao

PROFESSOR OF CIVIL ENGINEERING

JNTUA COLLEGE OF ENGINEERING

ANANTAPUR-515002

[email protected]

SRI. H. M. SOMASEKHARAIAH

RESEARCH SCHOLAR

J.N.T. UNIVERSITY

ANANTAPUR - 515002

[email protected]

DR.VAISHALI. G.GHORPADE

ASSOCIATE PROFESSOR IN CIVIL ENGINEERING DEPT.

JNTUA COLLEGE OF ENGINEERING

ANANTAPUR-515002

[email protected]

Dr.H.Sudarsana Rao et al. / International Journal of Engineering Science and Technology (IJEST)

ISSN : 0975-5462 Vol. 3 No. 8 August 2011 6266



Abstract

To increase the applications of Glass Fibre Reinforced High-Performance-Concrete (GFRHPC) in India, greaterunder standing of GFRHPC produced with locally available materials and indigenously produced mineral

admixtures is essential. In the present investigation, GFRHPC has been produced with locally available

aggregates and fly ash as the mineral admixture. Various fly ash based GFRHPC mixes were designed byabsolute volume method. Cubes of 150X150X150 mm size and cylinders of 150X300mm were cast and cured

for 28 days and then tested for compressive and tensile strengths to asses the strength characteristics ofGFRHPC. Workability has been measured by conducting compaction factor test on fresh GFRHPC mixes. Theexperimental results indicate that fly ash can be successfully utilized in producing good quality Glass Fibre

Reinforced High-Performance-Concrete. The various results which indicate the effect of fly ash and glass fibres

on the strength and workability characteristics of high-performance-concrete are presented in this paper to drawuseful conclusions.

Keywords: Fly ash, High Performance Concrete, Glass fibres

1. INTRODUCTION

The set back in the health of newly constructed concrete structures promoted the most directed and

unquestionable evidence of the last two/three decades on the service life performance of our construction and

the resulting challenge that confronts us is the alarming and unacceptable rate at which our infrastructuresystems all over the world are suffering from deterioration when exposed to real environments. When thegeneral performance concrete is substantially higher than that of normal type concrete, such concrete is regarded

as High Performance Concrete (HPC). Concrete may be regarded has high performance for several different

reasons: High strength, High workability, High durability-and perhaps also improved visual appearance. HPC

produced with the use of glass fibres is known as Glass Fibre Reinforced High Performance Concrete(GFRHPC). In India the applications of GFRHPC are very limited due to the lack of mix proportions, and

proper understanding of its behavior. There are no specified codes and provisions for usage of GFRHPC.

Fly ash is the finely divided mineral residue resulting from the combustion of ground or powdered coalin electric generating plant (ASTM C 618). Fly ash consists of inorganic matter present in the coal that has been

fused during coal combustion. This material is solidified while suspended in the exhaust gases and is collected

from the exhaust gases by electrostatic precipitators. Since the particles solidify while suspended in the exhaust

gases, fly ash particles are generally spherical in shape. Fly ash particles those are collected in electrostatic precipitators are usually silt size (0.074 - 0.005 mm). Due to its pozzolanic nature, FA is a beneficial mineral

admixture for concrete. It influences many properties of concrete in both fresh and hardened state. Moreover,

utilization of waste materials in cement and concrete industry reduces the environmental problems of power

plants and decreases electric costs. Utilization also reduces the amount of solid waste, greenhouse gas emissions

associated with Portland clinker production, and conserves existing natural resources.Hassan et al. [2000] presented the influence of two mineral admixtures, silica fume and fly ash on the

properties of super-plasticized high-performance concrete. The results indicated that usage of the mineral

admixtures improved the properties of high performance concrete. Gopalakrishna et al. [2001] presented the performance of HPC mixes having different replacement levels of cement with low calcium fly ash (class F) and

reported a compressive strength of 80 MPa with 25 % replacement of cement with fly ash and also concluded

that fly ash concretes have superior durability properties. Long et al. [2002] presented studies on very high

performance concretes with ultra fine powders such as pulverized fly ash (PFA), pulverized granulated blastfurnace slag (PS) and silica fume (SF) and reported that the use of ultra fine powders improved the relative

density of compound pastes with low w/b ratios. Goh et al. [2003] carried out laboratory tests to characterize the

properties of municipal fly ash as a blended cement material and reported that higher mortar strength than that

of control mortar cubes was achieved by replacement of OPC with municipal fly ash up to 10%. Uzal and

Turanli [2003] presented studies on blended cements containing a high volume of natural pozzolan and theyreported that blended cements containing 55% natural pozzolan showed excellent ability to reduce the alkali-

silica expansion. Isaia et al. [2003] presented the studies on physical and pozzolanic action of mineral additionson the mechanical strength of high performance concrete. Bhatty et al. [2006] presented utilization of discarded

fly ash as a raw material in the production of Portland cement. Their studies revealed that using fly ash is beneficial in cement plants and power plants. Jerath and Hanson [2007] presented the effects of fly ash

replacement of Portland cement and the use of dense aggregate gradation on the durability of concrete mixturesin terms of permeability. They found that, by the use of dense graded aggregate and increasing the fly ash

content from 35 to 40% the durability of concrete mixtures increased. They also observed the reduction in the

charge passed, when conducted rapid chloride ion permeability tests thus indicating increase in durability. Wang





and Li [2007] presented the mechanical performance of engineered cementitious composites incorporating high

volume fly ash. In view of these results, it is proposed to study the effect of fly ash as a partial replacement tocement in the production of Glass Fibre Reinforced High Performance Concrete.

2. Experimental Program

In order to study the behavior of GFRHPC and also to understand the influence of mineral admixturelike fly ash, a total number of 16 mixes have been tried. In all the mixes the same type of aggregate i.e. crushed

granite aggregate; river sand has been used. The proportion of cement, sand and aggregate has been maintained

same for all mixes. These relative proportions have been obtained by absolute volume method. OrdinaryPortland cement of 53 Grade from a single batch has been used. The test program consisted of carrying out

Compressive strength test on cubes and split tensile strength test on cylinders. The nomenclature of the mixes

studied in this investigation is presented in Table 1 which is self explanatory.

Table: 1 Nomenclature of Mixes Studied

S.NoDesignation of

mixMix Details No of cubes cast

No of Cylinders

cast

1 R Reference Mix M20 6 6

2 P A 0Reference HPC mix with0% glass fibre,

0% Fly ash6 6

3 P A 10

HPC Mix with 0% glass fiber, 10% Fly

ash 6 6

4 P A 20HPC Mix with 0% glass fiber, 20% Fly

ash6 6

5 P A 30HPC Mix with 0% glass fiber, 30% Fly

ash6 6

6 GF B 0GFRHPC Mix with 0.5 % glass fiber,

0% Fly ash6 6


10% Fly ash6 6


20% Fly ash6 6


30% Fly ash6 6

10 GF C 0GFRHPC mix with 1% glass fibre, 0%

Fly ash6 6


Fly ash6 6


Fly ash6 6


Fly ash6 6

14 GF D 0

GFRHPC mix with 1.5% glass fibre,

0% Fly ash 6 6

15 GF D 10GFRHPC mix with 1.5% glass fibre,

10% Fly ash6 6


20% Fly ash6 6


30% Fly ash6 6





2.1 Materials

2.1.1 CementOrdinary Portland cement of 53 grade conforming to ISI standards has been procured and the

properties of the cement are presented in Table 2.

Table. 2 Properties of Cement

S.No. Test Experimental values

Suggested values as per I.S

Specification

1 Fineness of Cement 4.52% <10.0%

2 Specific gravity 3.10 --

3 Normal consistency 33% --

4

Setting time

Initial setting time

Final setting time

40min

6 hours

Min 30 minutes

Max 10 Hours

5Compressive Strength at

3 days

7 days

28 days

30 N/mm2

42 N/mm2

56 N/mm2

23.0 N/mm2

33.0 N/mm2

53.0 N/mm2

2.1.2 Fine Aggregate: -

The locally available Pandameru river sand conforming to grading zone-II of IS 383-1970 has been used asFine Aggregate. The physical properties of fine aggregate are presented in Table 3.

Table 3: Physical Properties of Fine Aggregate

S. No. Property Value

1 Specific Gravity 2.67

2 Fineness Modulus 2.77

3 Bulk Density

i) Loose

ii) Compacted

14.67 kN/m3

16.04 kN/m3

4 Grading Zone - II

2.1.3 Coarse Aggregate

a) The locally available crushed granite material has been used as coarse Aggregate and its physical

properties are presented in Table 4.

Table 4 Physical properties of coarse aggregate

S. No. Property Coarse aggregate

1 Specific gravity 2.75

2 Bulk density

LooseCompacted

13.29 KN/m3

15.00 KN/m3

3 Water absorption 0.7%

4 Flakiness index 14.22%

5 Elongation index 21.33%

6 Crushing value 21.43%

7 Impact value 15.5%

2.1.4. Glass Fibre: -

In this investigation Cem-FILL Anti rack HD fibres have been used. It is a special purpose high

dispersion alkali resistant glass fibre chopped strand designed for mixing with concrete, mortar and othercement-based mixes, uniform dispersion of the fibres is needed. These fibres have a sizing system which is

water dispersible, allowing full dispersion into individual filaments in mixing in an aqueous environment. They

incorporate easily into mixes giving a very large number of distributed reinforcing fibres from a small weight of

product.





Cem-FIL® fibers offer superior performance to standard fiber reinforcing with widely varying addition rates

designed to meet specific project specifications. Anti Crack fibres do not protrude from the surface and requireno further finishing. The details are presented in Table 5

Table 5(a) Properties of Glass Fibres

S.No Property Value

1

2

34

5

Filament Diameter

Filament per stand

lengthUltimate Elongation%

Specific Gravity

14 Micron

100

12 mm2.4

2.68

Table 5 (b) Technical characteristics

Strand Tex Filament Dia(micron) StandardLength(mm) Moisturecontent (%) Size content(%) Filaments/ Kg

(Millions)

ISO 1889:1987 ISO 3344:1977 ISO 1887:1980

306 14 12 < 0.3 1.0 212

2.1.5. Water: -

Clean potable fresh water, which is free from concentration of acid and organic substances, has beenused for mixing the concrete.

2.1.6 Fly Ash

Locally available fly ash from a near by thermal power station has been used and its chemical

composition is presented in Table 6. Table 6 Chemical composition of fly ash

SI. No. Characteristics Percentage

1

23

4

56

7

8

Silica SiO2

Alumina Al2 O3

Iron oxide Fe2O3

Lime CaO

Magnesia MgOSulphur tri oxide SO3

Loss of ignition

Surface area m2/kg

49-67

16-284-10

0.7-3.6

0.3-2.6

0.1-2.1

0.4-1.9

230-600

2.1.7 Super PlasticizerThe super plasticizer used in this experiment is SP 337. It is manufactured by FOSROC, Bangalore. It

complies to IS: 9103 – 1999 and also to BS, ASTM Standards. On adding to concrete, it disperses the cement particles i.e. enhances the workability without much affecting the set rate of concrete. In the presentinvestigation super plasticizer is used only to improve workability of the concrete.

3 Fabrication and Casting:-

Cubes were cast in steel moulds of inner dimensions of 150 x 150 x 150mm and cylinders were cast in steelmoulds of inner dimensions as 150mm diameter and 300mm height for every mix. The cement, sand and fly ash

were mixed thoroughly by manually. Then glass fibre is added to the above mixture. For all test specimens,

moulds were kept on table vibrator and the concrete was poured into the moulds in three layers by tamping witha tamping rod and the vibration was effected by table vibrator after filling up the moulds. The moulds are kept in





vibration for one minute and it was maintained constant for all the specimens. Six cubes and three cylinders

were cast for each mix.

4 Curing:-

The moulds were removed after 24 hours and the specimens were kept immersed in a clear water tank. Aftercuring the specimens in water for a period of 28 days the specimens were removed out and allowed to dry under

shade. Six cubes, three cylinders were cast for each mix and the average strengths have been considered.

5.0 Results and Discussion

5.1 Effect of percentage replacement of cement by Fly Ash on workability of GFRHPC:

The variation of compaction actor workability with percentage of Cement replacement by fly ash is presented

Fig. 1 & 2

Fig. 1 Compaction Factor Vs. % of Fly ash for different glass fibre ratio

Fig. 2 Compaction Factor Vs. % of glass fibre for different Fly ash ratio





Observing Fig. 1 it can be noticed that the compaction factor of GFRHPC mixes decrease with increase

in the percentage replacement of cement by Fly ash indicating a decrease in workability with increase of Fly ashcontent. Similar trend is observed for all percentages of Glass fibre ratios tried in this investigation. This

decrease in workability may be attributed to the higher surface area of Fly ash leading to greater water demand.

For a given water-binder ratio, Fly ash based GFRHPC mixes possessed lesser compaction factor workabilitywhen compared to corresponding plain HPC mixes. At 0% replacement level, the decrease in compaction factor

workability is in the ranges of 6.44%, 9.95% and 14.29 for glass fibre ratios 0.5 %, 1% and 1.5% with respect to

reference plane GFRHPC Mix PA 0. At 10% replacement of cement by Fly ash, the decrease in the compactionfactor workability is in the ranges of 2.58%, 8.90%, 12.30% and 16.51% for glass fibre ratios 0%, 0.5 %, 1%

and 1.5% with respect to reference plane GFRHPC Mix PA0. At 20% replacement of cement by Fly ash, the

decrease in the compaction factor workability is in the ranges of 5.15%, 11.36%, 14.64% and 18.75% for glassfibre ratios 0%, 0.5 %, 1% and 1.5% with respect to reference plane GFRHPC Mix PA0. Similarly at 30%

replacement of cement by Fly ash, the decrease in the compaction factor workability is in the ranges of 7.26%,

13.23%, 16.51% and 20.49% for glass fibre ratios 0%, 0.5 %, 1% and 1.5% with respect to reference planeGFRHPC Mix PA0. Thus, it can be observed that, at ten percent replacement of cement by Fly ash the decrease

in the compaction factor is very much marginal. At 10% replacement level, the minimum compaction factor is

around 0.741 for the mix GFD10. For most of other mixes with different values of glass fibre ratios (0 to 1.5%),the compaction factor is lesser than 0.741. Also, it is observed that these mixes are quite cohesive even at lower

water-binder ratio 0.35 because of the super plasticizer used in the mix. Hence, it can be concluded that 10%

Fly ash based GFRHPC can be produced to have sufficient workability.

5.2 Effect of percentage replacement of cement by fly ash on 7 days and 28 days compressive strength of

Glass fibre reinforced high performance concrete:The variation of 7 days cube compressive strength with varying percentage of fly ash is presented in

Fig. 3.

0 5 10 15 20 25 30

40

45

50

55

60

65

70

7 D a y s c u b e c

o m p r e s s i v e s t r e n g t h M P a

% of Fly ash

0% Glass fibre

0.5% Glass fibre

1.0% Glass fibre

1.5% Glass fibre

Fig. 3 7-Days Cube Compressive Strength vs. % of Fly ash

From this figure, it can be observed that the 7 days compressive strength of GFRHPC mixes increases

with increase in percentage of fly ash up to 10% replacement level. It can further be observed that the maximumcompressive strength is obtained at 10% fly ash value. Further increase in percentage of fly ash, decreases the 7

days compressive strength. At 20% and 30% fly ash for different percentage of glass fibre the 7 days

compressive strength is even less than the plain mix value hence it can be concluded that the maximumreplacement of cement by fly ash as mineral admixture is 10%. A maximum increase of 6.67% is observed at 7

days age for PA10 mix. But by adding glass fibre a maximum increase of 27.21% is observed at 7 days age for

GF C 10 mix.

The variation of 28 days cube compressive strength with percentage of fly ash is presented in Fig. 4.





0 5 10 15 20 25 30

55

60

65

70

75

80

85

90

95

100

2 8 D a y s C u b e C o m p r e s s i v e s t r e

n g t h ( M p a )

% of Fly ash

0% Glass fibre

0.5% Glass fibre

1.0% Glass fibre

1.5% Glass fibre

Fig. 4 28-Days Cube Compressive Strength vs. % of Fly ash

It can be observed that the 28 days cube compressive strength also increases with percentage of fly ash.

The addition of fly ash enhances the load carrying capacity of the mix. The maximum cube compressive

strength is obtained at 10% replacement of fly ash further increase in fly ash decreases the value of compressivestrength. The percentage increase in compressive strength of GFRHPC at 10% fly ash is 3.33% for PA 10 mix

and 22.81 for GF C 10 mix over plain mix PA 0

5.3 Effect of glass fibre ratio on compressive strength of glass fibre reinforced high performance concrete:

The variations of 7 days cube compressive strength with varying percentage of glass fibre are presented

in Fig. 5. It can be observed that the 7 days compressive strength of GFRHPC mixes increases with increase in

percentage volume of glass fibres. It can further be observed that the maximum compressive strength is obtained

at 1% of glass fibre. Further increase in percentage of glass fibre, decreases the 7 days compressive strength as

observed at 1.5% of glass fibre. Hence it can be concluded that addition of glass fibre also contributes to

compressive strength of the mix. Similar observation was made by earlier researchers using fibres. A maximum

increase of 25.90% is observed at 7 days age for GF C 10 mix, over reference mix PA0





Fig. 5 7-Days Cube Compressive Strength vs. % of Glass fibres

The variation of 28 days cube compressive strength with volume percentage of glass fibres is depicted

in Fig. 6.

-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6

60

70

80

90

100

2 8 D a y s C

u b e C o m p r e s s i v e s t r e n g t h ( M p a )

% of Glass fibre

0% Fly ash

10% Fly ash

20% Fly ash

30% Fly ash

Fig. 6 28-Days Cube Compressive Strength vs. % of Glass fibres





It can be observed that the 28 days cube compressive strength also increases with percentage of glass

fibres 0, 0.5 and 1%. The addition of glass fibres enhances the load carrying capacity of the mix. It is observedthat the maximum compressive strength attained is at 1% of glass fibre ratio in the present investigation. Further

increase in percentage of glass fibre i.e., 1.5% decreases the value of compressive strength. The percentage

increase compressive strength of GFRHPC at 1% glass fibre is 22.81% for GF C 10 mix over reference mixPA0.

5.4 Effect of percentage replacement of cement by Fly ash on 28 days Split tensile strength.The 28 days tensile strengths of different GFRHPC mixes obtained from the present investigation are reported

in Fig. 7.

Fig. 7 28-Days Split Tensile Strength vs. % of fly ash

It can be observed from Fig. 7, there is an increase in tensile strength with addition of fly ash as mineral

admixture. There is increase in tensile strength at 10% of fly ash of PA10 mix, and for GM C 10 mix. Thereason for increase in tensile strength is due to pozzolanic activity of the admixture. Also, the addition of fly ash

improves the quality of transition zone and also contributes for achieving a denser mix. Further increase in

percentage of fly ash decreases the tensile strength. The percentage increase of PA10 mix over reference mix R

is 4.24%. And the maximum percentage increase in tensile strength at 10% of fly ash for GF C 10 mix is 23.32

over reference PA 0 mix.

5.5 Effect of Glass fibre ratio on Tensile strength of GFRHPC

The variation of 28 days split tensile strength with volume percentage of glass fibres is depicted in Fig.

8. It can be observed from this figure that the 28 days split tensile strength increases with increasing volume percentage of glass fibres i.e., 0, 0.5 and 1%. Further increase in percentage of glass fibre decreases the tensile

strength. This result is justified because addition of glass fibres with higher tensile strength can definitely

contribute to the tensile strength of the matrix. It is observed that the percentage increase in tensile strength ismaximum at 1% of glass fibre i.e., for the mix GF C 10. The percentage increase in tensile strength of GFRHPC

for GF C10 mix is 26.20% over reference mix PA 0. Thus it can be observed that addition of glass fibres has

significantly increased the split tensile strength. The major lacuna of low tensile strength of concrete mix can bethus be alleviated by using GFRHPC. The decrease in tensile strength at 1.5% glass fibre may be due to

formation of fibre lumps at higher fibre dosage.





Fig. 8 Split Tensile Strength vs. % of Glass fibres

6 Conclusions

From the experimental work carried out and the analysis of the results following conclusions seem to be valid

with respect to the utilization of fly ash in the production of GFRHPC.

Compaction factor workability of GFRHPC mixes decreases with increase in the percentagereplacement of cement by Fly ash indicating a decrease in workability with increase of Fly ash content.

This trend is observed for all percentages of Glass fibre ratios.

It is observed that, at ten percent replacement of cement by Fly ash the decrease in the compactionfactor is very much marginal. At 10% replacement level, the minimum compaction factor is around 0.741

for the mix GFD10. Also, it is observed that these mixes are quite cohesive even at lower water-binderratio 0.35 because of the super plasticizer used in the mix. Hence, it can be concluded that 10% Fly ash

based GFRHPC can be produced to have sufficient workability.

The 7-day compressive strength of GFRHPC mixes increases with increase in percentage of fly ash up

to 10% replacement level. It can further be observed that the maximum compressive strength is obtained at

10% fly ash value.

The 28-day cube compressive strength also increases with increase in percentage of glass fibres i.e. 0,0.5 and 1%. The maximum compressive strength is attained at 1% of glass fibre ratio in the present

investigation. The percentage increase in compressive strength of GFRHPC at 1% glass fibre is 22.81% for

GF C 10 mix over reference mix PA0.

There is an increase in tensile strength with addition of fly ash as mineral admixture up to 10%

replacement levels. The percentage increase of PA10 mix over reference mix R is 4.24%. And the

maximum percentage increase in tensile strength at 10% of fly ash for GF C 10 mix is 23.32 over referencePA 0 mix.

The split tensile strength of GFRHPC increases with increasing volume percentage of glass fibres up to

1%. Further increase in percentage of glass fibre decreases the tensile strength. The percentage increase in

tensile strength is maximum at 1% of glass fibre i.e., for the mix GF C 10. The percentage increase in

tensile strength of GFRHPC for GF C10 mix is 26.20% over reference mix PA 0. Thus it can be observedthat addition of glass fibres has significantly increased the split tensile strength. The major lacuna of low

tensile strength of concrete mix can be thus be alleviated by using GFRHPC.





References

1) Bhatty, JI., J Gajda, PE., Botha, F. and MM Bryant, PG. 2006. Utilization of Discarded Fly Ash as a Raw Material in the Production

of Portland cement . Journal of ASTM International, Vol. 3, No. 10, pp.

2) Goh, Chia-Chia., Show, Kuan-Yeow and Cheong, Hee-Kiat. 2003. Municipal Solid Waste Fly Ash as a Blended Cement Material.Journal of Materials in Civil Engineering, Vol. 15, No. 6, pp. 513-53-23.

3) Gopalakrishna, S., Rajamane, N.P., Neelamegam, M., Peter, J.A. and Dattatreya, J.K. 2001. Effect of partial replacement of cement

with fly ash on the strength and durability of HPC . The Indian Concrete Journal, pp. 335-341.4) Hassan, K.E., Cabrera, J.G., and Maliehe, R.S. 2000. The Effect of Mineral Admixtures on the Properties of High-Performance

Concrete. Cement & Concrete Composites, Vol. 22, pp. 267-271.

5) Isaia, G. C., Gastaldini, A. L. G. and Moraes, R. 2003, Physical and pozzolanic action of mineral additions on the mechanical

strength of high-performance concrete, Cement & Concrete Composites, Vol. 25, pp. 69-76.

6) Jerath, Sukhvarsh P.E. and Hanson, Nicholas. 2007. Effect of Fly Ash Content and Aggregate Gradation on the Durability of Concrete

Pavements. Journal of Materials in Civil Engineering, Vol. 19, No. 5, pp. 367-375.

7) Long, Guangcheng., Wang, Xinyou and Xie, Youjun. 2002. Very-High-Performance Concrete with Ultra fine Powders. Cement and

Concrete Research, Vol. 32, pp. 601-605.

8) Uzal, B. and Turanli, L. 2003, Studies on blended cements containing a high volume of natural Pozzolans, Cement and Concrete

Research, Vol. 33, pp. 1777-1781.

9) Wang, Shuxin and Li, Victor C. 2007. Engineered Cementitious Composites with High-Volume Fly Ash. Materials Journal of ACI,Vol. 104, No. 3, pp. 233-241.



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