strength and behaviour of fly ash based steel fibre reinforced … · saravana raja mohan. k,...

INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING

Volume 2, No 1, 2011

© Copyright 2010 All rights reserved Integrated Publishing services

Research article ISSN 0976 – 4399

Received on September, 2011 Published on November 2011 318

Strength and behaviour of Fly Ash based Steel Fibre Reinforced Concrete

Composite Saravana Raja Mohan. K, Parthiban. K

Associate Dean and Assistant Professor,

School of Civil Engineering, SASTRA University, Thanjavur

[email protected]

ABSTRACT

This experimental investigation is to study the effects of replacement of cement (by weight)

with five percentage of fly ash and the effects of addition of steel fiber composite. A control

mixture of proportions 1:1:49:1.79 with w/c of 0.45 was designed. Cement was replaced

with five percentages (10%, 15%, 20%, 25% & 30%) of Class C fly ash. Four percentages of

steel fibers (0.15%, 0.30%, 0.45% & 0.60%) having 20 mm length were used. This study

reports the feasibility of use of steel fibres and their effect due to variation in fibre length,

fibre content on structural properties such as cube compressive strength, cylinder

compressive strength, split tensile strength, modulus of rupture and modulus of elasticity of

this composite. Tests were conducted on beams with optimum fibre parameters, and the

results compared with those of identical Reinforced Concrete beam.

Keywords: Concrete Composites, fibre, fly ash, mechanical and structural properties

1. Introduction

The infrastructure needs of our country is increasing day by day and with concrete is a main

constituent of construction material in a significant portion of this infra-structural system, it is

necessary to enhance its characteristics by means of strength and durability. It is also

reasonable to compensate concrete in the form of using waste materials and saves in cost by

the use of admixtures such as fly ash, silica fume, etc. as partial replacement of cement. One

of the many ways this could be achieved by developing new concrete composites with the

fibres which are locally available that makes even non-engineered construction can work well

under severe loads like earthquakes or man-induced attacks.

To bring into focus the use of steel fibres in concrete, an experimental programme was

planned to study the material characteristics and structural components like beams. Here in

this paper, work on material properties and structural performance is reported. In this

experimental investigation, the structural properties of the steel fibre reinforced concrete have

been determined.

2. Materials and Method

2.1 Research Significance

The use of fly ash in concrete is abounded with data from mechanical and chemical strengths

(Job Thomas and Syam Prakash, 1993) to assess the material parameters. Studies focusing on

material properties with different percentage replacement of cement with fly ash are

presented (Goplakrishnan et al., 2001) and on structural component with use of fly ash

concrete and fibre concrete composites (Saravanarajamohan et al., 2003). It has been found

Strength and behaviour of Fly Ash based Steel Fibre Reinforced Concrete Composite

Saravana Raja Mohan. K, Parthiban. K

International Journal of Civil and Structural Engineering

Volume 2 Issue 1 2011

319

that with high volume of class ‘F’ fly ash, (Rafat Siddique, 2003) the workability of concrete

has increased and the amount of cube compressive strength, split tensile strength, flexural

strength has been decreased and no significant effect has been noted on impact strength of

plain concrete. The tests results obtained from fibre reinforced concrete (Sekar, 2004)

indicated that the addition of waste fibres obtained from wire winding industries and lathe in

plain concrete enhances the strength markedly, whereas waste fibres from wire drawing

industry reduced the strength of concrete. But studies focusing on application of this type of

composites are very few and hence there is a need to assess the structural properties of fibre

reinforced concrete composites using different locally available natural and artificial fibres

and this need is taken care of in this study.

2.2. Sample preparation

A mix proportion of 1:1.49:1.79 with suitable water cement ratio to get a characteristic

strength of M20 was considered for this study. The exact quantity of materials for each mix

was calculated. The parameters varied were fibre length, fibre content and fly ash percentage.

The constituent of materials used for making the concrete were tested and the results are

furnished in Table1. The cement, fine aggregate, coarse aggregate and fly ash were tested

prior to the experiments and checked for conformity with relevant Indian standards. Steel

fibre and fly ash were also tested to evaluate its tensile strength and compressive strength.

Table 1: Details of Constituent Materials

Material Description

Cement Type – OPC 43 grade

Fly Ash & % Class C Ash ( Neyveli Lignite), 10, 15, 20, 25, 30

Fine Aggregate River sand falling on zone III having a Fineness Modulus of 2.5

Coarse Aggregate 20mm nominal size aggregate, Fineness Modulus = 8.75

Steel fibre φ = 1 mm, Tensile strength = 300 Mpa

Fibre length 20,40,60,80mm Aspect ratio – (20), (40), (60), (80)

Mix ratio 1:1.49:1.79

w/c ratio 0.45

2.3 Material properties

Specimens were fabricated for various parameters to study its effect on the structural

properties of concrete. Table 2 gives the specimens prepared to study the mechanical

properties such as compressive strength, tensile strength, modulus of elasticity and structural

properties, modulus of rupture, according to standard procedure. The test results of the

different fibre reinforced concrete specimens have been compared with plain concrete.

Table 2: Details of Specimens

Properties Tested Size in mm Number of

specimens

7,14,28 Days cube Compressive strength 150x150x150 3 each

Cylinder Compressive strength 300x150φ 3

Split Tensile strength 300x150φ 3

Modulus of Rupture [Prism] 500x100x100 3





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Table 3 gives the different designation for various mixes corresponding to fibre length, fibre

content and fly ash percentage used for particular mix reflect the composite control of

concrete. For example S15F0.15 means 15% fly ash and 0.15% of fibre content.

Table 3: Details of Fibre & Fly Ash Parameters Used In Batches

Fibre content in percentage by weight Fibre length

in mm

Fly ash

% by wt. 0.00 0.15 0.30 0.45 0.60

20 10 10/0 10/0.15 10/0.30 10/0.45 10/0.60

40 15 15/0 15/0.15 15/0.30 15/0.45 15/0.60

60 20 20/0 20/0.15 20/0.30 20/0.45 20/0.60

80 25 25/0 25/0.15 25/0.30 25/0.45 25/0.60

100 30 30/0 30/0.15 30/0.30 30/0.45 30/0.60

2.3.1 Cube Compressive Strength

Compressive strengths of the cubes were tested for 7- days, 14-days and 28-days and the test

results are given in Table 4. The maximum compressive strength was 29.20 MPa, obtained

for S10F0.3 for a mix with a fibre length of 20mm, 10% fly ash and fibre content of 0.30%

by weight and the increase in strength over plain cement concrete was found to be 54.82%.

Table 4: Results of Cube Compressive Strength

Average Cube Compressive Strength in MPa Designation

7 Day 14 Day 28 Day

SF0/0 15.05 17.47 18.86

S10F0.15 18.95 22.75 28.74

S10F0.30 18.85 22.86 29.20

S10F0.45 18.56 22.76 28.54

S10F0.60 18.98 22.54 28.68

S15F0.15 18.00 22.35 28.95

S15F0.30 19.65 21.95 28.86

S15F0.45 19.36 21.66 28.95

S15F0.60 18.23 21.42 27.54

S20F0.15 17.98 20.55 27.26

S20F0.30 17.86 20.34 27.86

S20F0.45 17.35 20.98 27.00

S20F0.60 17.56 21.00 26.45

S25F0.15 17.25 20.25 26.58

S25F0.30 16.34 20.34 26.35

S25F0.45 16.21 20.15 26.68

S25F0.60 16.85 19.96 26.34

S30F0.15 15.58 19.48 25.45

S30F0.30 15.25 19.25 25.34

S30F0.45 15.64 18.54 25.68

S30F0.60 15.74 18.78 24.98

The variation of 7 day, 14-day and 28 day cube compressive strength with respect to the steel

fibre content and fly ash percentage is given in Figure 1. The 7-day compressive strength of

the flyash-based steel fibre concrete was found to be as high as 18.85MPa, which is 25.24 %

more than the ordinary concrete. As the fibre content increases, the strength of the composite





321

also increases. It is found that the loss in compressive strength due to the addition of fly ash

could be easily counterbalanced through the addition of fibres.

Figure 1: Effect of Flyash and Fibre content on Compressive Strength

However, at the age of 28 days, the increase in pozzolonic activity of the fly ash was

sufficient to contribute to the compressive strength. Thus the efficiency of the fly ash to act as

cementitious material has increased substantially at the age of 28 days.

2.3.2 Cylinder Compressive Strength

The properties such as Cylinder Compressive strength, Split tensile strength, Modulus of

rupture and the Modulus of elasticity were determined for 28-days and the test results are

given in Table 5. The variation of cylinder compressive strength with respect to the fly ash

percentage, fibre length and fibre content is given in Figure 2. The maximum cylinder

compressive strength is 25.45MPa, which is 45.85% more than the ordinary concrete. It is

observed that the variation of cylinder compressive strength is very much similar to the cube

compressive strength.

Table 5: Results of Modulus of Elasticity

Designation

28 day Cylinder

Compressive

Strength

MPa

Split Tensile

Strength

in

MPa

Modulus of

Rupture

in

MPa

Modulus of

Elasticity

in

MPa x104

SF0/0 17.45 2.60 2.89 2.17

S10F0.15 25.45 3.25 4.50 2.52

S10F0.30 24.56 3.65 4.50 2.47

S10F0.45 23.32 3.75 4.50 2.43

S10F0.60 23.5 4.00 4.56 2.76

S15F0.15 22.95 3.50 4.50 2.65

S15F0.30 22.98 3.75 4.50 2.89





322

S15F0.45 22.52 3.50 4.50 2.82

S15F0.60 22.35 3.25 4.50 2.78

S20F0.15 21.24 3.70 4.25 2.64

S20F0.30 21.57 3.00 4.00 2.64

S20F0.45 21.48 3.25 4.25 2.58

S20F0.60 21.74 3.00 4.00 2.43

S25F0.15 21.34 2.75 3.75 2.35

S25F0.30 20.94 2.70 3.75 2.52

S25F0.45 20.58 2.50 3.75 2.37

S25F0.60 20.65 2.50 3.75 2.28

S30F0.15 20.14 2.40 3.50 2.16

S30F0.30 19.98 2.40 3.50 2.18

S30F0.45 19.76 2.50 3.50 2.25

S30F0.60 19.62 2.50 3.50 2.24

Figure 2: Effect of Flyash and Fibre content on Compressive Strength

2.3.3 Split-Tensile Strength

In each mix, three standard cylinder specimens were tested to determine the splitting tensile

strength. The variation of the splitting tensile strength with respect to fly ash percentage, fibre

length and fibre content is given in Figure 3.





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Figure 3: Effect of Flyash and Fibre content on Split Tensile Strength

The maximum value of splitting tensile strength obtained is 4.0 MPa, which is about 53.84 %

more than ordinary concrete. The maximum strength was obtained for a mix (S10F0.60) with

fibre length 20 mm, fibre content 0.60 % by weight and 10 % fly ash replacement of cement.

2.3.4 Modulus of Rupture

The variation of flexural strength values with respect to fly ash percentage, fibre length and

fibre content is shown in Figure 4. The maximum Flexural strength obtained for Steel Fibre

Reinforced Concrete was 4.56 MPa and that for Plain Cement Concrete was 2.80 MPa. The

corresponding strength improvement is 57.78%. It is observed during testing that the plain

concrete specimens failed without any warning, whereas Fibre Reinforced Concrete

specimens showed a ductile failure, giving ample warning.

Figure 4: Effect of Flyash and Fibre content on Modulus of Rupture





324

2.3.5 Modulus of Elasticity

Modulus of elasticity was computed from the load deformation characteristics of the cylinder

specimens of size 300mm height and 150mm diameter. The variation of the modulus of

elasticity value with respect to fly ash percentage, fibre length and fibre content is shown in

Figure 5.

Figure 5: Effect of Flyash and Fibre content on Modulus of Elasticity

3. Variation of Fibre Content

Normalized cube strength variations with steel fibre are given in Figure 6. The 28 day cube

strength is in increasing order.

Figure 6: Normalised cube strength variation with steel fibre





325

The experimental results were translated into stress-strain curves for comparison with

concrete with the strain at 0.002 for yield and 0.0035 for failure, as specified in the codes.

The curve for the SFRC composites with 15% fly ash and 0.15% fibre volume are shown in

Figure 7.

Figure 7: Stress strain variation of composites

It may be seen that there is considerable increase in yield stress at 0.002 strain and the

significant point is the considerable increase in failure strain which goes as high as 0.007.

This feature helps one to utilize these composites advantageously for resisting seismic loads.

3. Structural Performance

Based on material strength characteristics it was decided to test beams with 15% fly ash and

0.3% fibre content. To bring into focus the role of fly ash concrete composites, it was decided

to use the composites in three different levels to evaluate the effectiveness of the composites

in resisting bending loads which are given in Table 6.

Table 6: Designation of different beams tested

Type of Fibre Designation Types of Beam

SQDB Steel Fibre Quarter depth composite beams

SHDB Steel Fibre Half depth composite beams Steel Fibre

SFDB Steel Fibre Full depth composite beams

To study the structural performance of SFRC, three SFRC beams of size 1600 x 100 x100mm

were cast with three fibre parameters, one prototype beam of the same size was also cast and

were tested in servo controlled loading frame as shown in Figure 8. Deflection of the

prototype beams was measured at mid span using Linear Variable Differential Transformers

(LVDTs).





326

Figure 8: Loading setup

Beams of different types of fibre parameters were tested under two point loading upto failure

and a typical result for SFRC is given in Table 7. This procedure is repeated for all the

specimens for SQDB, SHDB and SFDB for steel fibres. All these results relate to 15% flyash

and 0.3% fibre content and these values are chosen based on material strength characteristics.

Table 7: Peak loads and mid span deflections for beams

Test Series Peak load in kN Displacement at peak load (mm)

RCC 35 4.24

SQDB 72 12.5

SHDB 67 7.20

SFDB 65 5.15

Based on these results load-deflection curves are drawn and this is shown in Figure 9. Load-

deflection behavior is dependent on the loading conditions and true material behavior will

only be reflected in terms of the method and rate of loading, specimen geometry and the

nature of the test fixtures. The fixtures used here were taken to be infinitely rigid compared

to the test specimens. The load deflection is also very sensitive to the crack location and as

cracks seek the weakest section within the constant moment region rupture occurs.





327

Figure 9: Load Deflection Variations for SFRC Beams

It may be seen that in general the ductility or deflection increase as compared to normal

concrete is higher and correspondingly the loads show more increments for steel fibre quarter

depth beam as compared the other two. It is observed that the cracks were formed between

the loading points as shown in Figure 10. Generally the decay in stiffness – load deflections

is observed in all cases with the possibility of sustaining the loads at longer deformations

significantly in steel fibre quarter depth composites.

It may clearly be observed that the beams with quarter depth and half depth fibre composites

showing better performance over the full depth beams. This indicates the effective

redistribution capacity of SFRC beams.

4. Conclusion / Suggestions/ Findings

Based on experimental test, it is found that fly ash can serve as a good substitute for cement

in reasonable proportions by volume and whatever deficiencies that may result can be easily

overcome by use of steel fibres. Properties of the resulting composites show better

performance than plain concrete both in terms of mechanical and structural strengths. In

addition, the stress-strain curves show reasonable amount of energy absorption capabilities

with good ductility. Based on these test results it is now possible to find out enhancements in

strengths for different fly ash contents and fibre percentages by weight. An ideal choice

would be 15% fly ash with 0.15% of fibre gives an increase of 5% to 31 % increase in cube

strength at the end of seven days and 12% to 55% at the end of 28 days. Similar

enhancements in tensile strength and modulus of rupture are observed making these

composites an efficient material over concrete with the use of local materials and technology.

In general steel fibre composites show better performance upto 20% fly ash and 0.3% fibre

content. Optimum could be 0.15% fibre content at 10 or 15% fly ash giving a range of 12 to

54.82 % increase.

Acknowledgement





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The authors would like thank to Prof. R. Sethuraman, Vice Chancellor, SASTRA University,

Thanjavur, Tamil Nadu, India for the financial support and Dr. N. Lakshmanan, Former

Director, Structural Engineering Research Centre (SERC), Taramani, Chennai for the

guidance and permission to do the testing work at SERC, Chennai.

5. References

1. ACI Committee – 544 (1973), “State-of-the-Art Report on Fibre Reinforced

Concrete”, ACI Journal, 70(11), pp 729-742.

2. Swamy R.N (1974), “Fibre-reinforced Concrete: Mechanics, Properties and

Applications”, Indian Concrete Journal, 48(1), pp 7-16.

3. Ghosh, S, Bhattacharya, C and Ray, S.P (1989), “Tensile Strength of Steel Fibre

Reinforced Concrete”, IE (I) Journal –CI, 69, pp 222-227.

4. Job Thomas and Syam Prakash, V (1999), “Strength and Behaviour of Plastic Fibre

Reinforced Concrete”, Journal of Sructural Engineering (SERC), 26(3), pp 187-192.

5. IS-456: 2000, Code of Practice for Plain and Reinforced Concrete (Fourth Revision),

Bureau of Indian Standards, New Delhi, India.

6. Goplakrishnan, 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”, Indian. Concrete Journal, 75(5), pp 335-341.

7. Rafat Siddique (2003), “Properties of concrete incorporating high volumes of class F

flyash and san fibres”, Concrete & Research journal, 34(1), pp 37-42

8. Saravanarajamohan K, Jayabalan, P, and Rajaraman, A (2003), “Studies on fly ash

concrete composites”, Proceeding of International Conference on Innovative World

of Concrete, pp 102-105.

9. Saravanarajamohan K, Jayabalan, P, and Rajaraman, A (2003), “Performance

enhancement in concrete composites using local materials”, Proceeding of 28th

International conference on Our World of Concrete and Structures, Singapore, pp

413-420.

10. Sekar.T, (2004), “Fibre Reinforced Concrete from Industrial waste fibres – a

feasibility study”, IE(I) journal – CE, pp 287 – 290

11. Saravanarajamohan K, Jayabalan P, Rajaraman A and Lakshmiprabha T, (2004),

“Role of Fly ash Concrete Composites in Resisting Seismic Damage”, Proceeding of

International conference on Structural and Foundation Failures, ISFF, August,

Singapore.

strength and behaviour of fly ash based steel fibre reinforced … · saravana raja mohan. k,...

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