international journal of civil engineering and ... of... · 2.4 steel fibre reinforced self...

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),

ISSN 0976 – 6316(Online) Volume 3, Issue 2, July- December (2012), © IAEME

94

EFFECT OF STEEL FIBRES ON THE STRENGTH AND BEHAVIOUR

OF SELF COMPACTING RUBBERISED CONCRETE

N.Ganesan*, Bharati Raj, A.P.Shashikala & Nandini S.Nair

Dept. of Civil Engineering, National Institute of Technology Calicut, Kerala, India-673601

*Author to whom correspondence should be addressed. E-mail Id: [email protected]

Contact of other authors: [email protected], [email protected] ,

[email protected]

ABSTRACT

The concepts of sustainability and sustainable development are receiving greater attention

nowadays as the causes of global warming and climatic change are discussed in various

forums. Since, concrete is the most widely used construction material on earth, sustainable

technologies for concrete construction allow for reduced cost, conservation of resources,

utilization of waste materials and the development of eco-friendly durable concrete.

Considering the above aspects, a cementitious composite known as Self Compacting

Rubberised Concrete (SCRC) was developed by adding scrap rubber to Self Compacting

Concrete (SCC). The investigations on the engineering properties of SCRC revealed that there

is a systematic reduction in compressive, tensile and flexural strength of SCC on addition of

scrap rubber. In order to improve the foresaid engineering properties of SCRC, steel fibres

were added to the composite and the properties of Steel Fibre Reinforced Self Compacting

Rubberised Concrete (SFRSCRC) were evaluated. Also, a general regression equation

correlating various engineering properties of the composite was developed.

Keywords: brittleness, compressive strength, elasticity, flexural strength, rubber, self

compacting concrete, steel fibres

1. Introduction

The problem of waste accumulation exists worldwide, specifically in the densely populated

areas. Most of the non-degradable waste materials are left as stockpiles, used as landfill

material or illegally dumped in selected areas. Large quantities of this waste cannot be

eliminated. However, the environmental impact can be reduced by making more sustainable

use of this waste [1]. Researches into new and innovative uses of waste materials are

continuously advancing. These research efforts try to match society’s need for safe and

economic disposal of waste materials.

The disposal of used tyres is a major environmental problem causing environmental hazards

throughout the world. Therefore, there is an urgent need to identify alternative outlets for

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ISSN 0976 – 6308 (Print) ISSN 0976 – 6316(Online)

Volume 3, Issue 2, July- December (2012), pp. 94-107

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IJCIET

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95

these tyres, with the emphasis on recycling the waste tyres. The reuse of waste tyre rubber in

the production of concrete, where tyre rubber can be used as a partial replacement to natural

aggregates is an emerging field in this context. The use of rubber aggregates saves natural

resources and dumping spaces, and helps to maintain a clean environment. Hence, over the

past few years, various researches have been focused on the use of waste tyres in different

shapes and sizes in concrete [2]. Preliminary studies show that workable Rubberised Portland

Cement Concrete (Rubcrete) mixtures can be made provided that appropriate percentages of

tyre rubber are used in such mixtures [3].

The development of Self Compacting Concrete (SCC) with the unique property of flowing

under its own weight by Okamura (1988) [4,5] was with the prime aim of solving the problem

of honeycombing and giving better finishes to structures [6], especially where congestion of

reinforcement occurs. One of the innovations in Self Compacting Concrete technology was

the replacement of aggregates using waste materials like rice husk ash, marble dust, recycled

aggregates, silica dust, scrap rubber, glass aggregates, etc to produce sustainable concretes

due to their superior structural performance, environmental friendliness and low impact on

energy utilization [7]. The possibility of developing SCC incorporating rubber aggregates was

a novel approach to combine the advantages of both SCC and Rubberised concrete. Self

Compacting Rubberised Concrete (SCRC) requires slightly higher amount of super plasticizer

than conventional SCC having the same water/powder ratios to attain the required self-

compacting properties [8]. Even though this seemed to be a promising technology in

controlling the microstructure of concrete to obtain more versatile and innovative mechanical

behavior, very few studies have been carried out so far on Self Compacting Rubberised

Concrete [3, 8-11].

Studies have revealed that the addition of steel fibres improves the engineering properties of

concrete like ductility, post crack resistance, energy absorption capacity etc. Inclusion of steel

fibres imparts pseudo-ductility to brittle concrete with a significant increase in the tensile

strain capacity which increases the flexural strength, cracking resistance and toughness

characteristics [12, 13]. These properties are highly required for the structures in the present

scenario of frequently occurring earthquakes. However, no attempts have been made so far to

evaluate the effect of addition of steel fibres to Self Compacting Rubberised Concrete.

This paper focuses on the feasibility of adding steel fibres to Self Compacting Rubberised

Concrete. An attempt has been made to critically examine the engineering properties of

SFRSCRC mixtures, such as self compactability, compressive strength, split tensile strength,

flexural strength, modulus of elasticity and brittleness index.

2.1 Material

The materials used in this study include:

(i) Ordinary Portland cement conforming to IS: 12269-1987[13]

(ii) Fly ash with a normal consistency of 45% obtained from Neyveli Lignite Power Plant

and conforms to Type F as per ASTM C618 [14]

(iii) River sand passing through 4.75mm IS sieve conforming to grading zone II of

IS: 383-1970 [15] having specific gravity of 2.54

(iv) Coarse aggregate with a maximum size of 12mm and having a specific gravity of 2.77

(v) Shredded scrap rubber with a maximum size of 4.75mm

(vi) Crimped steel fibres having 0.45mm diameter and aspect ratio of 66



96

2.2 Mix design for Self Compacting Concrete (SCC)

The mix design based on the method proposed by Nan et.al [16] which, gives an indication of

the target strength after 28 days of curing, was carried out for obtaining concrete compressive

strengths of 20, 30, 40 and 50MPa. The water powder ratio (w/p) was varied so as to obtain

SCC mixes of various strengths and the mixes were checked for self compactability as per the

EFNARC [17] acceptance criteria for SCC. Naphthalene based super plasticiser Structuro 201

and viscosity modifying admixture (VMA) Calcium Sulphate dihydrate were added to impart

better workability and viscosity to the mix in order to avoid segregation. Table 1 gives the

details of the mix proportions of SCC.

2.3 Self Compacting Rubberised Concrete (SCRC)

Fine rubber was obtained by crushing the worn out tyres accumulated in the rubber waste

industry and sieved to get rubber particles with a maximum size of 4.75mm. The specific

gravity of fine rubber, thus obtained, was 1.14. In Self Compacting Rubberised Concrete

(SCRC), the fine aggregate was partially replaced by fine rubber and the percentage volume

of replacement (Rr) was 15%.

When fine aggregate was replaced with fine rubber, the mix was found to be less workable

and hence, the quantity of super plasticiser was increased, so that the mixes satisfy the

acceptance criteria of SCC. The viscosity modifying admixture was also added at the rate of

0.01% of the water content for imparting better workability and viscosity to the mixes and to

avoid segregation. The details of the constituents of the mix are given in Table.1. The self

compactability of the mixes was checked by Flow test, V-funnel test and L-Box test. Cube

specimens of 150mm size were cast for the SCC and SCRC mixes and tested for the 7 and 28

day compressive strengths. The fresh and hardened properties of the mixes are given in

Table.2.

Table 1 Mix proportion for SCC & SCRC

Designation Rr

(%)

Cement

(kg/m3)

Fly ash

(kg/m3)

Fine

Agg.

(kg/m3)

Coarse

Agg.

(kg/m3)

Scrap

Rubber

(kg/m3)

Super

plasticiser

(% of

powder

content)

VMA

(kg/m3)

w/p Water

(kg/m3)

SCC 20 0 196 211 887.00 710 - 0.50 - 0.50 202.00

SCRC 20 15 196 211 753.95 710 133.05 0.58 0.098 0.51 207.57

SCC 30 0 267 161 887.00 710 - 1.00 - 0.49 209.00

SCRC 30 15 267 161 753.95 710 133.05 1.26 0.134 0.50 214.00

SCC 40 0 339 130 887.00 710 - 1.30 - 0.44 205.00

SCRC 40 15 339 130 753.95 710 133.05 1.39 0.542 0.44 206.36

SCC 50 0 410 112 887.00 710 - 1.60 - 0.37 193.00

SCRC 50 15 410 112 753.95 710 133.05 1.66 0.533 0.38 198.36

Table 2 Self compactability of SCC and SCRC mixes

Designation Flow

(mm)

V-funnel

time (s)

L-box

(mm)

Compressive Strength

(MPa)

7-days 28-days

SCC 20 754 7.0 0.86 13.91 27.56



97

SCRC 20 740 9.0 0.84 10.17 19.56

SCC 30 750 8.0 0.86 25.60 37.50

SCRC 30 735 10.0 0.84 15.55 29.90

SCC 40 735 9.0 0.87 30.00 53.50

SCRC 40 720 11.0 0.85 20.85 40.10

SCC 50 723 10.5 0.89 37.50 62.00

SCRC 50 710 11.5 0.87 26.26 50.50

2.4 Steel Fibre Reinforced Self Compacting Rubberised Concrete (SFRSCRC)

Steel Fibre Reinforced Self Compacting Rubberised Concrete (SFRSCRC) was

obtained by adding crimped steel fibres having diameter 0.45mm, length 30mm

(aspect ratio 66) and ultimate tensile strength of 800MPa at volume fractions (Vf) of

0.25, 0.50, 0.75 and 1% to the SCRC mixes. Table.3 shows the mix proportions for the

SFRSCRC mixes.

Table 3 Mix proportion for SFRSCRC

Design

Strength

(MPa)

Vf

(%)

Cement

(kg/m3)

Fly ash

(kg/m3)

Fine

Agg.

(kg/m3)

Coarse

Agg.

(kg/m3)

Scrap

Rubber

(kg/m3)

Steel

fibres

(kg/m3)

Super

plasticizer

(% of

powder

content)

VMA

(kg/m3)

w/p Water

(kg/m3)

20

0.25 196 211 753.95 710 133.05 19.625 0.58 0.098 0.51 207.57

0.50 196 211 753.95 710 133.05 39.250 0.60 0.098 0.51 207.57

0.75 196 211 753.95 710 133.05 58.875 0.61 0.098 0.51 207.57

1 196 211 753.95 710 133.05 78.500 0.65 0.098 0.51 207.57

30

0.25 267 161 753.95 710 133.05 19.625 1.30 0.134 0.50 214.00

0.50 267 161 753.95 710 133.05 39.250 1.31 0.134 0.50 214.00

0.75 267 161 753.95 710 133.05 58.875 1.36 0.134 0.50 214.00

1 267 161 753.95 710 133.05 78.500 1.40 0.134 0.50 214.00

40

0.25 339 130 753.95 710 133.05 19.625 1.40 0.542 0.44 206.36

0.50 339 130 753.95 710 133.05 39.250 1.43 0.542 0.44 206.36

0.75 339 130 753.95 710 133.05 58.875 1.45 0.542 0.44 206.36

1 339 130 753.95 710 133.05 78.500 1.49 0.542 0.44 206.36

50

0.25 410 112 753.95 710 133.05 19.625 1.70 0.533 0.38 198.36

0.50 410 112 753.95 710 133.05 39.250 1.74 0.533 0.38 198.36

0.75 410 112 753.95 710 133.05 58.875 1.75 0.533 0.38 198.36

1 410 112 753.95 710 133.05 78.500 1.79 0.533 0.38 198.36

The following specimens were cast and tested for each mix to obtain the engineering

properties.

(i) 6 cube specimens of 150mm size to determine the unit weight and 28 day

compressive strength

(ii) 18 cylindrical specimens of 150mmΦ and 300mm height for the split tensile

strength, modulus of elasticity and brittleness index

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976

ISSN 0976 – 6316(Online) Volume 3, Issue 2, July

(iii) 6 prisms of 100 x 100 x 500mm for the modulus of rupture

3. Test Results and Discussions

3.1 Engineering properties of

The weights of SCC and SCRC cube specimens

determined. From Fig.1, it can be seen that t

lesser than that of conventional concrete and self compacting concrete. The density of

lightweight concrete can vary between 1200 to 2000kg/m

density range of 2300 to 2500kg/m

rubber replacements of 15% of the fine aggregate volume can be considered equivalent

to lightweight concrete.

Fig 1 Density of SCC and SCRC specimens

Fig 2 Compressive strength of SCC and SCRC specimens

The compressive strength of SCC and SCRC cube specimens are shown in

may be seen that, a decrease in compressive strength is observed for self compacting

rubberised composites in comparison with the control specimens.

reduction in compressive strength was found to be 23% for a rubber content of 15%.

One of the possible reasons for this compressive strength reduction may be the weak

0

500

1000

1500

2000

2500

Den

sity

(k

g/m

3)

0

10

20

30

40

50

60

70

Com

pre

ssiv

e S

tren

gth

(M

Pa

)

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 –

6316(Online) Volume 3, Issue 2, July- December (2012), © IAEME

6 prisms of 100 x 100 x 500mm for the modulus of rupture

Test Results and Discussions

Engineering properties of SCRC [19]

of SCC and SCRC cube specimens were obtained and the density was

, it can be seen that the average density of SCRC was 14%


ightweight concrete can vary between 1200 to 2000kg/m3 compared to the normal

density range of 2300 to 2500kg/m3. Hence, the self compacting concrete with fine

15% of the fine aggregate volume can be considered equivalent

Density of SCC and SCRC specimens

Compressive strength of SCC and SCRC specimens

The compressive strength of SCC and SCRC cube specimens are shown in


rubberised composites in comparison with the control specimens. The average



Mix Details

Mix Details

– 6308 (Print),

and the density was

he average density of SCRC was 14%


compared to the normal

. Hence, the self compacting concrete with fine

15% of the fine aggregate volume can be considered equivalent

The compressive strength of SCC and SCRC cube specimens are shown in Fig.2. It


The average





interface or the transition zone of the rubberised mortar and the conventional coarse

aggregates. These weak interfaces will act as the originators of micro cracks which

eventually grow to macro size leading to failure under compression.

Split tensile strength test was carried out on cylindrical specimens placed horizontally

between the loading surfaces of the compression testing machine. The load was

applied until failure of the cylinder along the vertical diameter was observed. The

results of split tensile strength are given in Fig.

strength of SCRC is similar to that of the compressive strength, the rate of reduction in

split tensile strength is very much lower when compared to the

mainly due to the ease with which the cracks can propagate under tensile loads. An

average reduction of 12 to 16% was observed in the split strength

specimens. The decrease in split strength of SCRC could be attributed to the same

factors that reduced the compressive strength.

Fig 3 Split Tensile strength of SCC and SCRC specimens

Fig 4 Modulus of rupture of SCC and SCRC specimens

Modulus of rupture (extreme fibre stress

under third-point loading. The flexural strength of the specimen was observed to be in

the range of 2.8 to 4.4N/mm2

Fig.4. The variation in modulus of rupture of Rubberised SCC is almost similar to that

0

1

2

3

4

5

Sp

lit

Ten

sile

Str

ength

(M

Pa)

0

1

2

3

4

5

Mo

du

lus

of

Ru

ptu

re (

MP

a)





ventually grow to macro size leading to failure under compression.



of the cylinder along the vertical diameter was observed. The

nsile strength are given in Fig.3. Although the variation of split tensile

is similar to that of the compressive strength, the rate of reduction in

ile strength is very much lower when compared to the compressive strength


average reduction of 12 to 16% was observed in the split strength

in split strength of SCRC could be attributed to the same

factors that reduced the compressive strength.

Split Tensile strength of SCC and SCRC specimens

Modulus of rupture of SCC and SCRC specimens

Modulus of rupture (extreme fibre stress in bending) was found out by testing prisms

point loading. The flexural strength of the specimen was observed to be in

for self compacting rubberised concrete as indicated in

. The variation in modulus of rupture of Rubberised SCC is almost similar to that

Mix Details

Mix Details

– 6308 (Print),





of the cylinder along the vertical diameter was observed. The

. Although the variation of split tensile

is similar to that of the compressive strength, the rate of reduction in

compressive strength


average reduction of 12 to 16% was observed in the split strength for SCRC

in split strength of SCRC could be attributed to the same

d out by testing prisms

point loading. The flexural strength of the specimen was observed to be in

ed concrete as indicated in

. The variation in modulus of rupture of Rubberised SCC is almost similar to that



of its split tensile strength. The strength in flexure increased with increase in the

compressive strength of concrete, but at a very slow rate.

It can be seen from Fig.5 that the elastic modulus increased with decrease in water

powder ratio, but, followed a decreasing pattern when

elastic modulus of SCRC was found to be lesser than the control

This reduction in the elastic modulu

of the composite encountered owing to the relatively low specific gravity and modulus

of rubber particles.

Fig 5 Modulus of elasticity of SCC and SCRC specimens

Fig 6 Brittleness Index of SCC and SCRC specimens

Brittleness Index of a concrete specimen in compression

100% of the elastic deformation energy to irreversible deformation energy

corresponding to the pre peak point of the stress

cylindrical specimens were loaded up to 80% of the ultimate load carrying capacity,

unloaded and then reloaded under compression. The brittleness index was calculated

based on the stress-strain hysteresis loops thus ob

Lower values of brittleness index indicate higher ductile deformation of the material.

0

5

10

15

20

25

30

35

Mo

du

lus

of

Ela

stic

ity

(G

Pa)

0

0.5

1

1.5

2

2.5

Bri

ttle

nes

s In

dex




compressive strength of concrete, but at a very slow rate.

at the elastic modulus increased with decrease in water

powder ratio, but, followed a decreasing pattern when scrap rubber was added. The

elastic modulus of SCRC was found to be lesser than the control specimens

This reduction in the elastic modulus could be due to the reduced compressive strength


Modulus of elasticity of SCC and SCRC specimens

Brittleness Index of SCC and SCRC specimens

Brittleness Index of a concrete specimen in compression is defined as the ratio of 80


corresponding to the pre peak point of the stress-strain curve [20]. The standard



strain hysteresis loops thus obtained and are indicated in Fig.


Mix Details

Mix Details

– 6308 (Print),


at the elastic modulus increased with decrease in water-

rubber was added. The

specimens by 19%.

s could be due to the reduced compressive strength


as the ratio of 80 -


]. The standard



d and are indicated in Fig.6.




101

The addition of scrap rubber in concrete reduces the brittleness index values and

improves the ductility of concrete, thus, enabling a transition from a brittle material to

a ductile one. This is due to the better energy absorption capacity of rubber, which

leads to plastic deformations at the time of fracture. The concrete ductility was

enhanced by about 31% for SCRC specimens.

3.2 Fresh properties of SFRSCRC

Table.4 shows the variation of self compactability of SFRSCRC mixes with increase

in the volume fraction of steel fibre. From the table, it may be noted that the increase

in fibre content caused a gradual reduction of about 7% in the values of slump flow

when compared to SCRC, irrespective of the strength of concrete. Beyond a fibre

volume fraction of 0.5%, the deformability of the mix in terms of the flow value was

found to decrease rapidly. The V-funnel time for SFRSCRC was almost same as that

of SCRC up to 0.5% volume fraction of steel fibres. Beyond 0.5%, the V-funnel time

was 11% higher than SCRC which sheds light on the enhanced apparent viscosity

(resistance to flow) of SFRSCRC. However, all the reported values were within the

desirable limits. The L-box values recorded from the test are given in the table, which

indicates that the passing ability ratio increased with increase in concrete strength

while it followed a decreasing trend with increasing fibre content, irrespective of the

compressive strength.

Table 4 Variation of self compactability with steel fibres

Vf (%)

Design Strength (MPa)

20 30 40 50 20 30 40 50 20 30 40 50

Flow value (mm) V-Funnel time (sec) L-box value (mm)

0.25 680 678 684 688 9 9 11 11 0.83 0.83 0.84 0.84

0.5 675 667 678 680 10 10 11 11 0.82 0.82 0.82 0.82

0.75 665 660 664 668 11 11 12 12 0.82 0.80 0.81 0.80

1 655 653 650 656 12 12 13 13 0.82 0.78 0.80 0.78

3.3 Hardened properties of SFRSCRC

3.3.1 Density

The weight of SFRSCRC cube specimens was measured and the density was

determined. The variation of density with the increasing fibre volume is given in Fig.7.

It was found that the density of the specimens increased with increase in fibre content.

The density of SFRSCRC is seen to fall in the range of 2000 to 2188kg/m3. Even

though the density was slightly higher for SFRSCRC specimens than SCRC, it was

lesser when compared to the density of SCC and conventional concrete which ranges

between 2300 to 2500 kg/m3.



Fig 7 Variation of density with fibre content

3.3.2 Compressive Strength

The variation of compressive strength with volume fra

An increase in compressive strength

volume fraction of 0.75%. At higher values of V

compressive strength was noted.

addition of scrap rubber was countered by the enhanced binding property in the

presence of fibres. The average

around 3.6%, 9.5% and 6.6% for fibre contents of 0.25, 0.5

For a volume fraction of 1%, the compressive strength was found to decrease by an

average of 16%. This decrease in the strength may be

entrapped air content when fibres are added

compressive strength if it does not change the air content, while the presence of air

content leads to a decrease in the compressive strength.

Lessard [21], an increase of 1% in the air content in High Performance Con

reduce the compressive strength by 4%.

most acceptable for volume fraction of 0.5%.

Fig 8 Variation of compressive strength with fibre content

1700

1800

1900

2000

2100

2200

2300

0

De

nsi

ty (

kg/

m3)

0

10

20

30

40

50

60

0 0.25

Co

mp

ress

ive

Str

en

gth

(M

Pa

)



Variation of density with fibre content

The variation of compressive strength with volume fraction of fibres is given in Fig.8

increase in compressive strength can be observed for SFRSCRC specimens up to

. At higher values of Vf, i.e., at 1%, in fact reduction in

compressive strength was noted. The reduction in compressive strength due

rubber was countered by the enhanced binding property in the

presence of fibres. The average increase in the compressive strength for all grades was

around 3.6%, 9.5% and 6.6% for fibre contents of 0.25, 0.50 and 0.75% respectively.


This decrease in the strength may be attributed to the increase of

when fibres are added. The fibre content slightly increases the


content leads to a decrease in the compressive strength. According to Aitcin and

, an increase of 1% in the air content in High Performance Con

reduce the compressive strength by 4%. The compressive strength was found to be

most acceptable for volume fraction of 0.5%.

Variation of compressive strength with fibre content

0.25 0.5 0.75 1

Fibre content

SCRC 20

SCRC 30

SCRC 40

SCRC 50

0.25 0.5 0.75 1

Fibre content

SCRC 20

SCRC 30

SCRC 40

SCRC 50

– 6308 (Print),

given in Fig.8.

SFRSCRC specimens up to a

, i.e., at 1%, in fact reduction in

The reduction in compressive strength due to the

rubber was countered by the enhanced binding property in the

compressive strength for all grades was

0.75% respectively.


attributed to the increase of

increases the


According to Aitcin and

, an increase of 1% in the air content in High Performance Concrete can

The compressive strength was found to be

Variation of compressive strength with fibre content



103

3.3.3 Split Tensile Strength

The variation of split tensile strength with fibre content is shown in Fig.9. The split

tensile strength was found to increase with increase in fibre volume fraction. The

average increase in split tensile strengths for all grades was found to be around 1.2%,

4.7% 3.1% and 1.5% for fibre contents of 0.25, 0.50, 0.75 and 1% respectively.

Fig 9 Variation of split tensile strength with fibre content

3.3.4 Modulus of Rupture

Fig.10 shows the variation of flexural strength with fibre volume fraction. It can be

seen that the flexural strength increased with increase in fibre volume fraction for all

grades of concrete. The average increase in modulus of rupture for all grades was

found to be around 3.2%, 4.9%, 3.3% and 1.7% for fibre contents of 0.25, 0.50, 0.75

and 1% respectively. The flexural strength was found to increase with increasing fibre

content, despite the decrease in compressive strength. This increase in the rupture

modulus may be attributed to the improvement of fibre-matrix interfacial bond.

Fig 10 Variation of modulus of rupture with fibre content

3.3.5 Modulus of Elasticity

Modulus of elasticity is the most important parameter that represents the elastic

properties of concrete and depends mainly on the property of the paste and the

2

2.5

3

3.5

4

4.5

5

0 0.25 0.5 0.75 1

Spli

t T

en

sile

Str

en

gth

(M

Pa

)

Fibre content

SCRC 20

SCRC 30

SCRC 40

SCRC 50

2

2.5

3

3.5

4

4.5

5

0 0.25 0.5 0.75 1

Mo

du

lus

of

rup

tue

(M

Pa

)

Fibre content

SCRC 20

SCRC 30

SCRC 40

SCRC 50



104

stiffness of the aggregates used. It can be seen from Fig.11 that the elastic modulus

increased with decrease in water-powder ratio, and also followed an increasing pattern

with higher fibre volume fractions. The elastic modulus of SFRSCRC was found to be

about 10% higher than that of SCRC. This increase in modulus of elasticity may be

due to the high modulus of elasticity of steel fibres. The bridging action of steel fibres

prevents the micro cracks from joining and thus arrests the sudden loss of strength.

Fig 11 Variation of modulus of elasticity with fibre content

3.3.6 Brittleness Index

From the variation of brittleness index with fibre content shown in Fig.12, it can be

noted that the brittleness index of SFRSCRC is about 4% less when compared to

SCRC. The decrease in brittleness index was notable at fibre volume fraction of 0.5%.

When compared to the SCC specimens, SFRSCRC showed an average decrease of

26% in brittleness index, which highlights the more ductile nature of rubberised

composites with steel fibres.

Fig 12 Variation of brittleness index with fibre content

0

5

10

15

20

25

30

35

0 0.25 0.5 0.75 1

Mo

du

lus

of

Ela

stic

ity

(G

Pa

)

Fibre content

SCRC 20

SCRC 30

SCRC 40

SCRC 50

0.6

0.8

1

1.2

1.4

1.6

1.8

0 0.25 0.5 0.75 1

Bri

ttle

ne

ss I

nd

ex

Fibre content

SCRC 20

SCRC 30

SCRC 40

SCRC 50



105

4. Correlation of engineering properties of SFRSCRC with the compressive

strength

The split tensile strength, flexural strength, modulus of elasticity and the brittleness

index of Steel Fibre Reinforced Self Compacting Rubberised Concrete could be

expressed in terms of its compressive strength.

A correlation equation of the general form:

� = �√�� (1)

has been formulated for all the engineering properties,

where �� represents the compressive strength of the mix and ‘�’ is a constant.

Y represents the engineering property of SFRSCRC.

The equations have correlation coefficients of 80% as shown in Fig.13. From the

figures, it could be noted that as the compressive strength increases, the engineering

properties of Steel Fibre Reinforced Rubberised Composites increases at a slow rate.

(a) Modulus of Elasticity (E) (b) Split Tensile Strength (STS)

(c) Modulus of Rupture (MR) (d) Brittleness Index (BI)

Fig 13 Correlation of engineering properties of SFRSCRC with compressive

strength

5. CONCLUSIONS

The critical investigation on the engineering properties of Steel Fibre Reinforced Self

Compacting Rubberised Concrete has paved way to realising the potentials of this

material for special application in the construction industry such as in seismic resistant

structures. The following conclusions were arrived at:

E = 4.0* (CS)0.5

R² = 0.839

0

5

10

15

20

25

30

35

0 20 40 60

Mo

du

lus

of

Ela

stic

ity

(G

Pa

)

Compressive Strength (MPa)

STS = 0.67* (CS)0.5

R² = 0.850

0

1

2

3

4

5

0 20 40 60

Spli

t T

en

sile

Str

en

gth

(M

Pa

)


MR = 0.7* (CS)0.5

R² = 0.9240

1

2

3

4

5

0 20 40 60

Mo

du

lus

of

rup

ture

(M

Pa

)


BI= 0.3* (CS)0.5

R² = 0.8100

0.5

1

1.5

2

0 20 40 60

Bri

ttle

ne

ss I

nd

ex




106

1. Even though SFRSCRC was found to have density slightly greater than SCRC,

it could be considered as a lightweight material owing to its reduced density in

comparison to conventional SCC as well as normal concrete. This property

would prove advantageous for seismic resistant structures.

2. The addition of steel fibres to SCRC up to a volume fraction of 0.5% has been

found to have a beneficial effect on the strength and modulus of elasticity of

SCRC mixes. The compressive strength of SCRC was increased by about 10%

for a fibre volume fraction of 0.5%.

3. Addition of scrap rubber results in reduction of elastic modulus of concrete,

which could be rectified to a certain extent by the addition of fibres. In

comparison to SCRC, the modulus of elasticity of SFRSCRC was found to

improve by an average of 10%, which could be attributed to the high modulus

of elasticity of steel fibres.

4. The brittleness index of SFRSCRC is very low compared to SCC mixes with

and without rubber. This low brittle nature of SFRSCRC could be exploited

well by using it in congested areas like beam column joints, which are to be

designed as ductile sections under seismic conditions.

All the engineering properties of SFRSCRC could be predicted from its 28-day

compressive strength with an effective correlation of 80% by means of regression

equations. It can be observed that all the evaluated properties are lying on the positive

side for SFRSCRC in comparison with Self Compacting Rubberised Concrete mixes.

Hence, it can be concluded that SFRSCRC offers numerous desirable characteristics

like improved strength, enhanced ductility, etc. for various structural applications.

Thus, SFRSCRC is having remarkable potentials to be considered as a “sustainable

functional material” for the construction industry.

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