toughness characteristics of steel fibre reinforced concrete
DESCRIPTION
Toughness Characteristics of Steel Fibre Reinforced ConcreteTRANSCRIPT
![Page 1: Toughness Characteristics of Steel Fibre Reinforced Concrete](https://reader038.vdocuments.us/reader038/viewer/2022100506/5528288655034675588b466f/html5/thumbnails/1.jpg)
“Toughness Characteristics of Steel Fibre Reinforced Concrete”
Biography:
Arumugam E is a professor of Civil Engineering, College of Engineering, Anna University,
India. He has obtained his B.E from Regional Engineering College, Tamilnadu; M.E from
P.S.G College of Technology, Tamilnadu and PhD from College of Engineering, Anna
University. His research interests include Stress Concentration, Fly ash concrete, Polymer
Concrete.
Nanda kumar S and Deviprasadh A are first year graduate students (M.E Construction
Engineering and Management) studying in College of Engineering, Anna University. They
both did their under-graduate in Hindustan College of Engineering, Chennai, and did their
project work in the above topic in Larsen & Toubro ltd, Chennai.
ABSTRACT
The objective of this investigation was to study the behaviour of Steel Fibre
Reinforced Concrete (SFRC). Hooked end fibres and corrugated (crimped) fibres with aspect
ratio of 55 were used. Specimens were cast without fibres and with fibres of 0.5% and 1%
volume fraction (Vf). Tests were conducted for studying the compressive, tensile, flexural
strength and energy absorption. Compressive and split tensile tests were conducted on cubes
and cylinders respectively. 15 Beams were cast and tested under two point loading to find
flexural strength, toughness and stiffness. An empirical equation for finding the toughness
index was developed based on fibre percentage. 30 panels were cast and tested under static
point load to calculate the energy absorption and ductility index.
Keywords: Steel Fibre Reinforced Concrete, Static load, Panels, Beams, Toughness,
Energy Absorption.
1
![Page 2: Toughness Characteristics of Steel Fibre Reinforced Concrete](https://reader038.vdocuments.us/reader038/viewer/2022100506/5528288655034675588b466f/html5/thumbnails/2.jpg)
INTRODUCTION
The advantages of using concrete include high compressive strength, good fire
resistance, high water resistance, low maintenance, and long service life. The disadvantages
of using concrete include poor tensile strength, low strain of fracture and formwork
requirement. Hence fibres are added to concrete to over come these disadvantages. The
addition of fibres in the matrix has many important effects. Most notable among the improved
mechanical characteristics of Fibre Reinforced Concrete (FRC) are its superior fracture
strength, toughness, impact resistance, flextural strength, resistance to fatigue etc. Improving
fatigue performance is one of the primary reasons for the extensive use of Steel Fibres in
concrete.
RESEARCH SIGNIFICANCE
Although many tests were carried out on FRC materials, they were mainly based on flexure
test on beam specimens. Very few literatures were available on testing of panels or slabs
which is similar to most practical cases. Hence an attempt was made in this work to study the
behaviour of square FRC panels simply supported on all sides and subjected to concentrated
load on its center, which is the severe loading in most practical cases.
EXPERIMENTAL INVESTIGATION
In order to study the interaction of steel fibres with concrete under compression, split tension,
flexure and static load, 45 cubes, 45 cylinders, 15 beams, 30 panels was casted respectively.
The experimental program was divided into five groups.
Each group consists of 9 cubes, 9 cylinders, and 3 beams, 3 panels of 50mm (1.97in)
thickness and 3 panels of 100 mm (3.94in.) thickness.
i.The first group is the control (Plain) concrete with 0% fibre (PCC)
ii.The second group consisted of hooked end steel fibre of Vf 0.5% (HSFRC 0.5)
![Page 3: Toughness Characteristics of Steel Fibre Reinforced Concrete](https://reader038.vdocuments.us/reader038/viewer/2022100506/5528288655034675588b466f/html5/thumbnails/3.jpg)
iii.The third group consisted of hooked end steel fibre of Vf 1.0% (HSFRC 1.0)
iv.The fourth group consisted of corrugated steel fibre of Vf 0.5% (CSFRC 0.5)
v.The fifth group consisted of corrugated steel fibre of Vf 1.0% (CSFRC 1.0)
SFRC beams of size 150x150x700mm (5.9 inch.x5.91inch.x27.56 inch.) were tested using a
servo controlled Universal Testing Machine (MTS) as per the procedure given in ASTM
C-78 and the load was applied at a rate of 0.1mm/min, load and displacement was recorded
constantly (Figure 5). Toughness was calculated as the energy equivalent to the area under the
load deflection curve as per the procedure given in the ASTM C-1018. Stiffness of the beam
specimen was found as the slope of the load-deflection curve upto the elastic region of the
curve.
The panel specimen of dimension was placed on a simply supported condition on all four
sides and a concentrated load was applied over an area of 9.46sq.inch. (61sq.cm).The actuator
as operated at a rate of 1.5 mm/min (0.06inch/min) and the corresponding load & deflection
was measured as per the European Specification for Sprayed Concrete (EFNARC). The
bottom deflection was also monitored using a Linearly Variable Differential Transducer
(LVDT) (Figure 3 and Figure 4). The testing was continued till a deflection of 25mm
(0.98inch) or failure which ever occurred earlier. The energy absorption upto the deflection
of25mm (0.98inch) was calculated as area under load deflection curve for that deflection,
with an increment of2mm (0.08inch). Ductility index was calculated as the ratio of the
deflection upto the ultimate load to the deflection upto the first crack load. The ultimate
deformation has been considered as the deformation corresponding to 15% load drop i.e. 85%
of the ultimate load. The ductility so calculated is called the displacement ductility.
Ductility (μd ) = Ultimate deflection (δu ) / Yield deflection (δy)
![Page 4: Toughness Characteristics of Steel Fibre Reinforced Concrete](https://reader038.vdocuments.us/reader038/viewer/2022100506/5528288655034675588b466f/html5/thumbnails/4.jpg)
Materials
The materials used and their specifications are as follows:
CEMENT
Ordinary Portland cement was used and its specific gravity is 3.15*. The brand used was
“UltraTech” with P53 grade.
FINE AGGREGATE
Specific gravity of fine aggregate is 2.65 with water absorption 0.99%. Dry loose bulk density
was calculated as1502 Kg/m3 (93.76lbm/cubic foot).
COARSE AGGREGATE
A crushed granite stone aggregate of maximum size of 20 mm was used. Specific gravity of
coarse aggregate is 2.73 with water absorption 0.25% and dry loose bulk density 1500 Kg/m3
(93.63lbm/cubic foot).
STEEL FIBRES
HOOKED END STEEL FIBRES
Hooked end steel fibres commercially called as Dramix steel fibres manufactured by Bekaert
Corporation were used which had a length of 30 mm (1.18inch) and a diameter of 0.55 mm
(0.022inch) resulting in an aspect ratio of about 55 and conforms to ASTM A820 and
Belgium standard 1857*.The tensile strength of fibre is in the range of 1100 N/mm2*
(156,456.78 lbf/square inch)
CORRUGATED STEEL FIBRES
Corrugated steel fibres from Stewols & Co - India were used which had a length of 25 mm
and a diameter of 0.45 mm resulting in an aspect ratio of about 55 and conforms to ASTM
A820*.The tensile strength of fibre is in the range of1200 N/mm2* (1,706,801.27lbf/square
inch)
Note: * as per the manufacturers report
![Page 5: Toughness Characteristics of Steel Fibre Reinforced Concrete](https://reader038.vdocuments.us/reader038/viewer/2022100506/5528288655034675588b466f/html5/thumbnails/5.jpg)
EXPERIMENTAL RESULTS AND DISCUSSION
Compressive Strength
The Compressive strength of concrete mixed with steel fibres was found to vary marginally.
50% of the 28 days strength of corrugated fibres was obtained in 3 days itself. The
compressive strength of ordinary concrete and fibre reinforced concrete are tabulated in
Table 1.
Split tensile strength
The split tensile strength was found to be increased as the percentage of fibre was increased.
For the hooked fibre with volume fraction of 0.5% and 1.0% the increase in tensile strength
was 8 % and 32.4%respectively. The increase was about 30% for corrugated fibres with
volume fraction of 1.0% and there was no increase in case of CSFRC (Corrugated Steel Fibre
Reinforced Concrete) of volume fraction 0.5%. The 28 days strength of 0.5% volume fraction
of HSFRC (Hooked Steel Fibre Reinforced Concrete) was 7% greater than that of CSFRC of
same volume fraction. The results are tabulated in table 1.
Flexure strength
The flexure strength was found to decrease marginally. The failure was brittle in case of plain
concrete and failure was ductile in case of steel fibre reinforced concrete. The addition of
steel fibre resulted in a consistent increase in ductility of the beams. The toughness index for
all the control beams was found to be 1. For all the SFRC beams the I5 and I10 values are
greater than 2.75 and 4 respectively. The toughness indices were calculated for all the
specimens and are tabulated in Table 2.
Empirical equation
The empirical equations for finding the toughness indices were found using the I5 and I10
values from the experimental results using Microsoft’s Excel office program which can be
seen in the Figure 1 and Figure 2.
![Page 6: Toughness Characteristics of Steel Fibre Reinforced Concrete](https://reader038.vdocuments.us/reader038/viewer/2022100506/5528288655034675588b466f/html5/thumbnails/6.jpg)
Energy absorption
The maximum load and energy absorbed are tabulated in Table 3. The peak load obtained
with steel fibre reinforced concrete was found to increase more than 2 times when compared
to control (plain) concrete of same thickness.
50mm (1.97inch) panels
For HSFRC with 0.5% and 1% volume fraction the energy absorbed was 27.5 and 32.4 times
that of control concrete. For CSFRC with 0.5% and 1% volume fraction the energy absorbed
was 19.4 and 32.8 times that of control concrete. The energy absorbed by 0.5% volume
fraction of HSFRC was 42% more than that of 0.5% volume fraction of CSFRC. The energy
absorbed by 1% volume fraction of HSFRC and CSFRC was almost equal. The energy
absorbed for 1% volume fraction of HSFRC was 17% more than that of 0.5% volume fraction
of HSFRC .The energy absorbed for 1% volume fraction of CSFRC was 69% more than that
of 0.5% volume fraction of CSFRC.
100mm (3.94inch) panels
For HSFRC with 0.5% and 1% volume fraction the energy absorbed was 18.6 and 15.6 times
that of control concrete. For CSFRC with 0.5% and 1% volume fraction the energy absorbed
was 10.5 and 13.7 times that of control concrete. The energy absorbed by 0.5% volume
fraction of HSFRC was 73% more than that of 0.5% volume fraction of CSFRC.
The energy absorbed by 1.0% volume fraction of HSFRC was 7.7% more than that of 1.05%
volume fraction of CSFRC. The energy absorbed for 0.5% volume fraction of HSFRC was
20% more than that of 1.0% volume fraction of HSFRC. The energy absorbed for 1% volume
fraction of CSFRC was 33% more than that of 0.5% volume fraction of CSFRC.
![Page 7: Toughness Characteristics of Steel Fibre Reinforced Concrete](https://reader038.vdocuments.us/reader038/viewer/2022100506/5528288655034675588b466f/html5/thumbnails/7.jpg)
Ductility
The ductility index for control concrete was found to be 1.00. The ductility index for all
SFRC panels was found to vary between 4to 5 for all 50mm thick panels and 2to3 for 100mm
panels. The energy absorbed for 1% volume fraction of CSFRC was 33% more than that of
0.5% volume fraction of CSFRC.
CONCLUSION
Based on the results of this experimental investigation the following conclusions are drawn:
1. Addition of steel fibres to concrete increases the compressive strength of concrete
marginally.
2. The tensile strength was found to be maximum with volume fraction of 1%.
3. The addition of fibres to concrete significantly increases its toughness and makes
the concrete more ductile as observed by the modes of failure.
4. The stiffness of beams was studied and was found to be maximum for hooked end
fibre with 1% volume fraction.
5. The ductility of steel fibre reinforced concrete was found to increase with increase
in volume fraction of fibres and the maximum increase was observed for hooked
fibres with 1% volume fraction.
6. The improvement in the energy absorption capacity of steel fibre reinforced
concrete panels with increasing percentage of steel fibre was clearly shown by the
results of the static load test on panels.
7. The 100mm thick panel absorbed the maximum energy of 1010Nm with Hooked
end steel fibre with volume fraction 0.5% for a deflection of 20mm.
![Page 8: Toughness Characteristics of Steel Fibre Reinforced Concrete](https://reader038.vdocuments.us/reader038/viewer/2022100506/5528288655034675588b466f/html5/thumbnails/8.jpg)
ACKNOWLEDGEMENT
The authors thank Larsen & Toubro ltd. for their technical and other facilities provided at
various stages of this research work. The authors express their sincere gratitude and heartfelt
thanks to Dr.B.Sivarama Sarma, Head, R&D, Larsen & Toubro ltd, Chennai for his
valuable guidance and supervision throughout the project work. The authors are grateful to
Dr.M.Neelamegam, Deputy Director, SERC, Chennai for his esteemed suggestions and
guidance for this work. The authors sincerely thank all others who have helped directly or
indirectly at various stages of this work.
REFERENCES
1. Basi, Z. and Kaiser, H. (April 2001) "Steel Fibres as Crack Arrestors in Concrete."
The Indian Concrete Journal.
2. Craig, R., S. Mahadev, C.C. Patel, M. Viteri, and C. Kertesz. "Behaviour of Joints
Using Reinforced Fibrous Concrete." Fibre Reinforced Concrete International
Symposium, SP-81, American Concrete Institute, Detroit, 1984, pp. 125-167.
3. Craig, R. McConnell, J. Germann, N. Dib, and Kashani, F. (1984) "Behaviour of
Reinforced Fibrous Concrete Columns." Fibre Reinforced Concrete International
Symposium, SP-81, American Concrete Institute, Detroit, pp. 69-105.
4. Gopalakrishnan, S. Krishnamoorthy, T.S. Bharatkumar,B.H. and Balasubramanian, K.
(December 2003) “Performance Evaluation of Steel Fibre Reinforced Shotcrete”
National seminar on advances in concrete technology and concrete structures for the
future, Annamalai University
5. Kaushik S.K., Gupta.V.K., and Tarafdar.N.K., (1987) “Behaviour of fibre reinforced
concrete in shear” proceedings of the international symposium on Fibre Reinforced
Concrete International Symposium, volume I, chapter II, pp 1.133-1.149
6. Krishnamoorthy, T.S. Bharatkumar, B.H. Balasubramanian, K. and Gopalakrishnan,
![Page 9: Toughness Characteristics of Steel Fibre Reinforced Concrete](https://reader038.vdocuments.us/reader038/viewer/2022100506/5528288655034675588b466f/html5/thumbnails/9.jpg)
S. (February 2000) “Investigation on durability characteristics of SFRC” Indian
Concrete Journal page 94-98
7. Marc vandevalle, N.V. and Ganesh, P. (March 2003) Fibres in Concrete Indian
Concrete Journal, pp 939-940
8. Marc vandevalle, N.V. (1998) “Tunnelling the world” Dramix reference manual
9. Sivarama Sarma, B. (1997) , “Investigations on laced reinforced concrete beams with
normal and fibre reinforced concrete under monolithic and cyclic loading” Ph.D
Thesis, IIT, Madras.
10. P.Srinivasalu, N.Lakshmanan, K.Muthumani, B.Sivarama Sarma (1987) “Dynamic
behaviour of fibre reinforced concrete” proceedings of the international symposium on
Fibre Reinforced Concrete International Symposium, volume I, chapter II, pp 2.85
11. Taylor, M.R. Laydon, F.D. and Barr, B.I.G. (October 1996) “Toughness
characteristics of fibre reinforced concrete”, Indian Concrete Journal, pp.525-531
TABLES AND FIGURES
List of Tables:
Table 1 - Results of Compressive and Tensile strength
Table 2 - Results of beam stiffness
Table 3 - Results of energy absorption and ductility index
List of Figures:
Figure 1 - Empirical equation for CSFRC
Figure 2 - Empirical equations for HSFRC
Figure 3 - Panel failure in static load
Figure 4 - Panel arrangement for test
Figure 5 - Beam arrangement for test
![Page 10: Toughness Characteristics of Steel Fibre Reinforced Concrete](https://reader038.vdocuments.us/reader038/viewer/2022100506/5528288655034675588b466f/html5/thumbnails/10.jpg)
Table 1 Results of Compressive and Tensile strength
Table 2 Results of beam stiffness
SpecimenID
LoadkN
(kip)
Deflectionmm
(inch)
28 days flexuralStrengthN/mm2
(lbf/squareinch)
Toughness indices Stiffness
(kN/mm)
(kip/inch)
I5 I10
Controlspecimens
34.00(7.64)
1.30(0.051)
6.04(875.73)
1.00 1.00 26.15(149.80)
28.50(6.41)
1.13(0.044)
5.06(733.64)
1.00 1.00 25.30(145.68)
30.00(6.74)
1.10(0.043)
5.33(772.77)
1.00 1.00 27.28(171.07)
Hookedfibre0.5%
28.50(6.41)
1.00(0.0394)
4.59(665.50)
3.26 5.00 28.50(162.69)
27.00(6.07)
1.30(0.051)
4.80(695.94)
3.44 4.67 20.77(119.02)
25.50(5.73)
0.90(0.035)
4.53(656.80)
3.18 4.86 28.33(163.71)
Hookedfibre1.0%
33.80(7.60)
1.00(0.0394)
6.00(869.93)
3.79 5.63 33.80(192.89)
31.50(7.08)
1.00(0.0394)
5.68(823.53)
4.16 5.88 31.50(179.70)
Specimen type Average Compressive strength N/mm2(lbf/square inch)
Average Tensile Strength N/mm2
(lbf/square inch)
3 days 7 days 28 days 3 days 7 days 28 days
Controlspecimens
25.27(3663.85)
39.59(5740.08)
59.89(8683.34)
2.55(369.72)
3.54(513.26)
4.81(697.39)
Hooked fibre0.5% vf
24.50(3552.21)
37.29(5406.61)
58.24(8444.11)
2.90(420.47)
4.76(690.14)
5.19(752.49)
Hooked fibre1.0% vf
26.32(3816.09)
38.04(5515.35)
59.01(8555.75)
4.01(581.40)
5.66(820.63)
6.37(923.588)
Corrugatedfibre 0.5% vf
27.38(3969.78)
39.76(5764.73)
58.43(8471.66)
3.40(492.96)
5.02(727.84)
4.83(700.29)
Corrugatedfibre 1.0% vf
40.35(5850.27)
32.17(4664.27)
60.00(8699.29)
3.82(553.86)
5.29(766.99)
6.27(909.08)
![Page 11: Toughness Characteristics of Steel Fibre Reinforced Concrete](https://reader038.vdocuments.us/reader038/viewer/2022100506/5528288655034675588b466f/html5/thumbnails/11.jpg)
32.00(7.19)
1.00(0.0394)
5.69(824.98)
3.81 6.23 32.00(182.49)
Corrugatedfibres0.5%
26.00(5.85)
1.00(0.0394)
4.62(669.85)
2.51 3.16 26.00(148.48)
27.00(6.07)
1.10(0.043)
4.80(695.94)
2.70 4.18 24.55(141.16)
27.20(6.12)
1.20(0.047)
4.80(695.94)
3.12 4.08 22.67(130.21)
Corrugatedfibres1.0%
26.50(5.96)
1.30(0.051)
4.71(682.89)
3.1 5.02 20.38(111.57)
27.50(6.18)
1.10(0.043)
4.80(695.94)
3.71 5.92 25.00(143.72)
29.00(6.52)
1.05(0.041)
5.16(748.14)
2.65 6.00 27.60(159.02)
Table 3 Results of energy absorption and ductility index
Specimen IDFirstcrackload kN(kip)
ExperimentalPeak load
kN(kip)
Energyabsorbedfor 20mmdeflection
Nm(lbs-foot)
Deflection upto0.15% ultimate
load drop mm
(inch)
DuctilityIndex
Control panel50mm
10.92(2.45)
_ 12.60(894.04)
1.56(0.06)
1.00
8.54(1.92)
_ 10.30(730.85)
2.31(0.091)
1.00
7.30(1.64)
_ 5.76(408.71)
1.51(0.06)
1.00
Control panel100mm
31.36(7.05)
_ 53.55(3799.69)
2.88(0.11)
1.00
40.04(9.00)
_ 56.00(3973.53)
3.06(0.12)
1.00
37.51(8.43)
_ 58.13(4124.66)
3.33(0.13)
1.00
Hooked 50mmwith 0.5%vf
10.56(2.37)
25.91(5.82)
288.50(20470.77)
10.75(0.42)
4.72
8.65(1.94)
15.92(3.58)
243.87(17304.01)
12.10(0.48)
5.45
10.38(2.33)
17.91(4.03)
259.50(18413.05)
13.00(0.51)
4.64
Hooked100mm with
0.5%vf
37.63(8.46)
77.62(17.45)
936.00(66414.69)
11.50(0.45)
3.73
44.83(10.08)
87.55(19.68)
1105.80(78462.99)
8.60(0.34)
2.56
![Page 12: Toughness Characteristics of Steel Fibre Reinforced Concrete](https://reader038.vdocuments.us/reader038/viewer/2022100506/5528288655034675588b466f/html5/thumbnails/12.jpg)
51.69(11.62)
84.26(18.94)
988.00(70104.39)
11.00(0.43)
2.46
Hooked 50mmwith 1.0%vf
9.87(2.22)
19.35(4.35)
327.50(23238.05)
10.15(0.40)
4.77
12.61(2.83)
23.94(5.38)
262.63(18635.14)
11.10(0.44)
7.87
9.30(2.09)
23.16(5.21)
338.25(24000.82)
10.00(0.39)
4.27
Hooked100mm with
1.0%vf
50.0(11.24)
94.00(21.13)
890.00(63150.72)
7.10(0.28)
2.08
33.43(7.52)
100.00(22.48)
952.70(67599.65)
10.00(0.39)
2.52
Corrugated50mm with
0.5%vf
8.75(1.97)
13.23(2.97)
164.50(11672.24)
9.00(0.35)
3.26
8.82(1.98)
18.74(4.21)
180.00(12772.06)
6.60(0.26)
4.47
11.4(2.56)
17.97(4.04)
211.44(15002.91)
10.1(0.40)
4.04
Corrugated100mm with
0.5%vf
46.58(10.47)
90.0(20.23)
544.00(38599.99)
6.75(0.27)
3.17
49.45(11.12)
62.59(14.07)
564.50(40125.54)
5.10(0.20)
1.93
46.20(10.39)
89.89(20.21)
644.25(45713.31)
6.80(0.27)
2.31
Corrugated50mm with
1.0%vf
11.15(2.51)
31.14(7.00)
361.50(25650.54)
9.10(0.36)
4.95
16.37(3.68)
21.78(4.90)
303.25(21517.37)
9.00(0.35)
4.37
9.57(2.15)
23.51(5.29)
274.25(19459.65)
10.75(0.42)
5.54
Corrugated100mm with
1.0%vf
41.06(9.23)
88.00(19.78)
791.00(56126.09)
8.10(0.32)
3.12
45.18(10.16)
95.00(21.36)
769.88(54627.50)
8.20(0.32)
3.00
![Page 13: Toughness Characteristics of Steel Fibre Reinforced Concrete](https://reader038.vdocuments.us/reader038/viewer/2022100506/5528288655034675588b466f/html5/thumbnails/13.jpg)
FOR I5 y = 0.7533x + 2.4FOR I10 y = 3.68x + 1.9667
0
2
4
6
8
10
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25Percentage of Fibre
Tou
ghne
ss I
ndic
es I5
I10
Expon.(I5)Expon.(I10)
Figure 1 Empirical equation for CSFRC
FOR I5 y = 1.2533x + 2.6667FOR I10 y = 2.14x + 3.7733
0
2
4
6
8
10
0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25Percentage of fibre
Tou
ghne
ss I
ndic
es I5
I10
Expon. (I5)Expon. (I10)
Figure 2 Empirical equations for HSFRC
![Page 14: Toughness Characteristics of Steel Fibre Reinforced Concrete](https://reader038.vdocuments.us/reader038/viewer/2022100506/5528288655034675588b466f/html5/thumbnails/14.jpg)
Figure 3 Panel failure in static load
Figure 4 Panel arrangement for test Figure 5 Beam arrangement for test