Stress-Strain Behaviour: Hybrid Fibre Reinforced Concrete Analysis

This report investigates the stress-strain behavior of M20 grade concrete with varying proportions of polypropylene and steel fibers. The objective is to determine the optimal combination of these hybrid fibers to enhance the concrete's compressive strength, flexural tensile strength, and split tensile strength. The methodology involves mixing M20 grade concrete with different percentages (0%, 0.5%, 1.0%, 1.5%, and 2.0%) of hybrid fibers, with varying ratios of polypropylene to steel fiber (100:0, 75:25, 50:50). The results indicate that the highest compressive strength is achieved with 1.5% hybrid fibers composed of 50% polypropylene and 50% steel fibers, leading to a maximum improvement of about 52.5% in compression strength, 117.5% in flexural tensile strength and 148% in split tensile strength. The study concludes that incorporating 1.5% of a hybrid fiber mixture containing 50% polypropylene and 50% steel fiber significantly improves the axial properties of M20 grade concrete.

STRESS-STRAIN BEHAVIOUR OF FIBRE
REINFORCED CONCRETE WITH
DIFFERENT
PROPORTIONS OF POLYPROPYLENE
AND STEEL FIBRE

Necessity of Hybrid Fiber Reinforced
Concrete
 Concrete is brittle in nature and could break easily (Khan and Jafri,
2015).
 Brittleness of concrete should be reduced (Kim, et al., 2016).
 Brittleness could be reduced by adding fibers to concrete (Rai1 and
Joshi, 2014).
 Performance of hybrid fiber reinforced concrete has not been given
much importance.

Objective of the Work
 To study the behaviour of concrete under axial compression due to
the addition of steel fibres (Vairagade and Kene, 2013) and
polypropylene in different proportions.
 To study the use of polypropylene (Dharan and Lal, 2016) and steel
fibres as materials to strengthen reinforced concrete.
 To study the stress-strain behaviour (de-Oliveira Jr. et al., 2010)
compressive strength (Sofi and Phanikumar, 2015), workability and
find the best combination of the materials to be used.

Methodology
 Mix M20 grade concrete (Goyal and Vikram, 2017) with different
percentages (0%, 0.5%, 1.0%, 1.5%, and 2.0%) of the hybrid fibers.
 The ratio of polypropylene and steel fibre would be varied as follows
100:0, 75:25, 50:50 so as to obtain different proportions of hybrid fibres.
 Each proportion of hybrid fibres are cast into 2 cylinders and 2 cubes.
 They are then tested using 200 Tons capacity CTM.
 Aspect ratio of steel fibre used is 55.

Sample preparation
 S1 = 100% polypropylene and 0% Steel fibers
 S2 = 75% polypropylene and 25% Steel fibers
 S3 = 50% polypropylene and 50% Steel fibers
 S1, S2 and S3 are mixed with M20 grade concrete in five
different proportions (0%, 0.5%, 1.0%, 1.5%, and 2.0%)

Results
Samples Compressive
Strength
Flexural
Tensile
Strength
Split Tensile
Strength
Compaction
Factor
M20 20 N/mm2 4 N/mm2 2.5 N/mm2 0.95
M20+ 0.5%S1 22.4 N/mm2 5.2 N/mm2 3.4 N/mm2 0.93
M20 + 1.0%S1 23.6 N/mm2 5.8 N/mm2 3.9 N/mm2 0.92
M20 + 1.5%S1 25.2 N/mm2 7.9 N/mm2 5.2 N/mm2 0.90
M20 + 2.0%S1 24.5 N/mm2 7.1 N/mm2 4.3 N/mm2 0.88
M20 + 0.5%S2 23.7 N/mm2 5.6 N/mm2 3.7 N/mm2 0.94
M20 + 1.0%S2 25.3 N/mm2 6.2 N/mm2 4.3 N/mm2 0.93
M20 + 1.5%S2 27.9 N/mm2 8.3 N/mm2 5.7 N/mm2 0.91
M20 + 2.0%S2 27.6 N/mm2 7.6 N/mm2 4.6 N/mm2 0.90
M20 + 0.5%S3 23.9 N/mm2 5.8 N/mm2 4.2 N/mm2 0.95
M20 + 1.0%S3 26.2 N/mm2 6.6 N/mm2 4.7 N/mm2 0.95
M20 + 1.5%S3 30.5 N/mm2 8.7 N/mm2 6.2 N/mm2 0.96

Stress – Strain Relationship

Discussions
 The results shown in the table indicates that the highest compressive
strength is obtained when M20 grade concrete is mixed with 1.5% of
hybrid fibers made up of 50% polypropylene and 50% steel fibers (Yet,
Hamid and Kasmuri, 2012).
 Both flexural and split tensile strength are also higher for the same
sample (i.e., the sample with 50% polypropylene and 50% steel fibers)
and it occurs when 1.5% of the sample is mixed with M20 grade
concrete.

Discussions Continued
 Compaction factor which indicates the workability of concrete is
also highest for the sample with 1.5% hybrid fiber and a percentage
of 50% steel fiber (Song and Yin, 2016) and 50% polypropylene.
 It could be seen from the graph that the stress-strain relationship is
also improved when 1.5% of hybrid fiber with a mixture of 50%
steel fiber and 50% polypropylene is used.

Discussions Continued
 Due to the addition of hybrid fibers there is a maximum
improvement of about 52.5% in the Compression Strength.
 The Flexural Tensile Strength has improved by a maximum of
117.5% due to the addition of hybrid fibers.
 The Split Tensile Strength has improved by a maximum of 148%
due to the addition of hybrid fibers.

Discussions Continued
 The workability of concrete decreases due to the addition of
polypropylene but improves due to the addition of steel fibers
(Razzak, and Ali, 2011).
 Addition of hybrid fibers improves the stress-strain characteristics
(Rizzuti and Bencardino, 2014). of M20 grade concrete.

Conclusion
 The best composition of hybrid fiber is 50% polypropylene with 50%
steel fiber as seen from the results shown above.
 Addition of 1.5% of hybrid fiber containing 50% polypropylene and
50% steel fiber improves the axial properties of M20 grade
concrete.
 Addition of hybrid fibers improves the compression strength,
flexural tensile strength and split tensile strength.