INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND ... OF... · 2.4 Steel Fibre Reinforced Self...
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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] ,
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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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
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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
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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
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(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
)
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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%
lesser than that of conventional concrete and self compacting concrete. The density of
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
may be seen that, a decrease in compressive strength is observed for self compacting
rubberised composites in comparison with the control specimens. The average
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
Mix Details
Mix Details
– 6308 (Print),
and the density was
he average density of SCRC was 14%
lesser than that of conventional concrete and self compacting concrete. The density of
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
may be seen that, a decrease in compressive strength is observed for self compacting
The average
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
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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)
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6316(Online) Volume 3, Issue 2, July- December (2012), © IAEME
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
ventually 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
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
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
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),
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
Split tensile strength test was carried out on cylindrical specimens placed horizontally
between the loading surfaces of the compression testing machine. The load was
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
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 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
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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
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6316(Online) Volume 3, Issue 2, July- December (2012), © IAEME
of its split tensile strength. The strength in flexure increased with increase in the
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
of the composite encountered owing to the relatively low specific gravity and modulus
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
100% of the elastic deformation energy to irreversible deformation energy
corresponding to the pre peak point of the stress-strain curve [20]. The standard
cylindrical specimens were loaded up to 80% of the ultimate load carrying capacity,
unloaded and then reloaded under compression. The brittleness index was calculated
strain hysteresis loops thus obtained and are indicated in Fig.
Lower values of brittleness index indicate higher ductile deformation of the material.
Mix Details
Mix Details
– 6308 (Print),
of its split tensile strength. The strength in flexure increased with increase in the
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
of the composite encountered owing to the relatively low specific gravity and modulus
as the ratio of 80 -
100% of the elastic deformation energy to irreversible deformation energy
]. The standard
cylindrical specimens were loaded up to 80% of the ultimate load carrying capacity,
unloaded and then reloaded under compression. The brittleness index was calculated
d and are indicated in Fig.6.
Lower values of brittleness index indicate higher ductile deformation of the material.
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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.
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976
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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
)
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6316(Online) Volume 3, Issue 2, July- December (2012), © IAEME
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.
For a volume fraction of 1%, the compressive strength was found to decrease by an
This decrease in the strength may be attributed to the increase of
when fibres are added. The fibre content slightly increases the
compressive strength if it does not change the air content, while the presence of air
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.
For a volume fraction of 1%, the compressive strength was found to decrease by an
attributed to the increase of
increases the
compressive strength if it does not change the air content, while the presence of air
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
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ISSN 0976 – 6316(Online) Volume 3, Issue 2, July- December (2012), © IAEME
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
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 3, Issue 2, July- December (2012), © IAEME
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
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 3, Issue 2, July- December (2012), © IAEME
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
)
Compressive Strength (MPa)
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
)
Compressive Strength (MPa)
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
Compressive Strength (MPa)
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 3, Issue 2, July- December (2012), © IAEME
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.
REFERENCES
1. Malek, B., Iqbal, M., Ibrahim, A., “Use of selected waste materials in concrete mixes”,
Waste Management 27 (2007) pp.1870–1876.
2. Gregory Marvin Garrick B.S., “Analysis and testing of waste tyre fibre modified
concrete”, MS Thesis, Louisiana State University, May 2005.
3. Topçu, İ.B., Bilir, T., “Experimental investigation of some fresh and hardened properties
of rubberised self-compacting concrete”, Materials and Design 30 (2009) pp.3056–3065
4. Okamura H., “Self-Compacting High-Performance Concrete”, Concrete International, V.
19, No. 7, July 1, 1997, pp. 50-54.
5. Okamura H., and Ouchi M., “Self Compacting Concrete”, Journal of Advanced Concrete
Technology, V. 1, No.1, April 2003, pp 5-15.
6. Gettu R., Shareef S.N., and Ernest K.J.D., "Evaluation of the robustness of SCC", Indian
Concrete Journal, V. 83, No. 6, 2009, pp. 13-19.
7. Elahi, A., Basheer, P.A.M., Nanukuttan, S.V., and Khan, Q.U.Z., “Mechanical and
durability properties of high performance concretes containing supplementary
cementitious materials”, Construction and Building Materials, V. 24, Issue 3, March
2010, pp. 292-299
International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online) Volume 3, Issue 2, July- December (2012), © IAEME
107
8. Bignozzi M.C., Sandrolini F., “Tyre rubber waste recycling in self-compacting
concrete”, Cement and Concrete Research 36 (2006) pp.735–739.
9. Garros, M., Turatsinze, A., Granju, J.L., “Effect of rubber aggregates from grinding of
end of life tires on the properties of SCC”, SP-235-12, Recent Advances in Concrete
Technology, pp.177-188.
10. Mehmet G., Erhan G., “Permeability properties of self-compacting rubberised
concretes”, Construction and Building Materials 25 (2011) pp.3319–3326.
11. Najim K.B., Hall M.R., “A review of the fresh/hardened properties and applications for
plain- (PRC) and self-compacting rubberised concrete (SCRC)”, Construction and
Building Materials 24 (2010) pp. 2043–2051.
12. Grunewald, S., Walraven, J.C., “Parameter-study on the influence of steel fibres and
coarse aggregate content on the fresh properties of self-compacting concrete”, Cement
and Concrete Research 31 (2001) pp.1793–1798.
13. Corinaldesi, V., Moriconi, G., “Durable fibre reinforced self-compacting concrete”,
Cement and Concrete Research, 34 (2004) July, pp. 249–254.
14. IS 12269: 1987, Indian Standard Specification for 53 grade Ordinary Portland Cement.
P.5.
15. ASTM C618 - 08a, Standard Specification for Coal Fly Ash and Raw or Calcined
Natural Pozzolan for Use in Concrete.
16. IS 383:1970 (R2002), Indian Standard Specification for coarse and fine aggregates from
natural sources for concrete P.12.
17. Nan, S., Kung-Chung, H., His-Wen, C., “A simple mix design method for self-
compacting concrete”, Cement and Concrete Research 31 (2001) pp. 1799–1807.
18. European Federation of Producers and Contractors of Specialist Products for Structures
(EFNARC), Specifications and Guidelines for Self Compacting Concrete, February
2002. www.efnarc.org
19. Bharati, R., Ganesan, N., Shashikala, A.P., “Engineering Properties of Self- compacting
Rubberized Concrete”, Journal of Reinforced Plastics and Composites, Vol.30, No.23,
December 2011, pp.1923-1930.
20. Topçu, İ.B., “Assessment of the brittleness index of rubberized concrete”, Cement and
Concrete Research, (1997) Vol. 27, No. 2, pp. 177-183.
21. Aitcin, P.C., and Lessard, M., “Statistical Analysis of the production of a 75MPa air-
entrained concrete”, Proceedings of the Symposium on the Utilisation of High-Strength
Concrete, Lillehamer, Norway, (1993) pp. 793-800.