EVALUATION OF ENGINEERING PROPERTIES FOR POLYPROPYLENE FIBRE REINFORCED CONCRETE

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International Journal of Advanced Engineering Technology
E-ISSN 0976-3945

IJAET/Vol.III/ Issue I/January-March, 2012/42-45




Research Article

EVALUATION OF ENGINEERING PROPERTIES FOR
POLYPROPYLENE FIBRE REINFORCED CONCRETE
Priti A. Patel
1
, Dr. Atul K. Desai
2
and Dr. Jatin A. Desai
3



Address for Correspondence
1
Assistant Professor, Civil Engineering Department, C.K. Pithawalla Engineering College, Surat, and Research
scholar, Applied Mechanics Department, SVNIT, Surat, Gujarat, India.
2
Associate Professor, Department of Applied Mechanics, Sardar Vallabhbhai National Institute of Technology,
Surat, Gujarat, India.
3
Retired Professor, Department of Applied Mechanics, Sardar Vallabhbhai National Institute of Technology, Surat,
Gujarat, India.
ABSTRACT
As concrete is the most commonly used material in construction, improvement of cementitious material become more and more
essential. Conventional concrete has two major drawbacks: low tensile strength and a destructive and brittle failure. In an attempt
to increase concrete ductility and energy absorption, polypropylene fibre reinforced concrete (PFRC) has been introduced. This
study is part of a research program on evaluating the performance of polypropylene fibre reinforced concrete. An experimental
investigation explored properties such as compressive strength, flexural strength, split tensile strength and shear strength of
polypropylene fibre reinforced concrete. The fibre volume fraction V
f
ranges from 0 to 2%. No significant change is found for
compressive strength but flexural, split tensile and shear strength improves greatly, when compared to the plain concrete.
KEYWORDS Fibre reinforced concrete, Polypropylene fibre, Flexural strength, Shear strength, Fibre volume fraction
INTRODUCTION
Concrete is a brittle material with low tensile strength
and low strain capacity that result in low resistance to
cracking. To improve such properties, fibre reinforced
concrete (FRC) has been developed (4). Fibres are
intended to improve tensile strength, flexural strength,
toughness and impact strength (2), to change failure
mode by means of improving post-cracking ductility,
and to control cracking (3). Tensile strength of the
composite, related more to the stress at which matrix
develops a macro-crack, will not differ much for most
conventional fibre reinforced cementitious materials.
Several fibre materials in various sizes and shapes have
been developed for use in FRC. Among these fibres,
the polypropylene
has been one of the most successful
commercial applications. The common forms of these
fibres are smooth-monofilament and have triangular
shape. Polypropylene fibres have some unique
properties that make them suitable for reinforcement in
concrete. The fibres have a low density, are chemically
inert and non corrosive.
The primary objectives of this investigation were to
determine the benefits of using polypropylene fibre
reinforced concrete (PFRC).
• To determine the properties of the fresh
concrete mixtures using fiber.
• To investigate and compare the properties of
hardened concrete for control and various
PFRC mixes.
• Observe the difference between failure
patterns of plain and PFRC specimens.
EXPERIMENTAL WORK:
Materials and Methods
OPC 53 grade cement, aggregate – maximum size of
9.5 mm and 19 mm, river sand and potable water are
used.
Super plasticizer – 140 ml/bag is used to achieve
adequate fiber dispersion and workability. Triangular
shaped polypropylene fibre of 12 mm length is used.
Density of fibre is 1400 kg/m
3
. The mixture
proportions and properties of concrete used in the test
program are given in Table 1.
Variable: Fibre volume fraction – 0%, 0.5%, 1%, 1.5%
and 2 %. From each mixture, the following specimens
are casted: three cubes (150x150x150mm), cylinders
(150mm dia. and 300 mm height), beams (100 x 100x
500mm), L- shape specimen for shear (Refer fig 1).
Specimens are tested at 7 and 28 days.
Table 1. Mixture Proportions
JSCE-SF6 suggested direct shear method by using
beam of size (150x 150x 500 mm) and load applied
through male–female arrangement and failure under
double shear. Another arrangement suggested by Dr.
C.D. Modhera and Dr. N. K. Bairagi, (1) was used to
find shear strength for this experimental work (Refer
fig 1). For testing the specimen, the loading
arrangement is designed such that the intended plane
for shear failure is in single shear.
Mix Ingredients Quantity
Cement (kg/m
3
) 383.16 kg/m
3

Water (kg/m
3
) 191.6 lit/m
3

Sand (kg/m
3
) 602.70 kg/m
3

Grit- 10 mm down (kg/m
3
) 490.90 kg/m
3

Aggregate- 20 mm down (kg/m
3
) 736.34 kg/m
3

w/c 0.5
Compressive strength(N/mm
2
) 28 days 32.29 N/mm
2

International Journal of Advanced Engineering Technology
E-ISSN 0976-3945

IJAET/Vol.III/ Issue I/January-March, 2012/42-45





Fig. 1: Shape of specimen and Loading arrangement for Shear Strength test
RESULTS AND DISCUSSION:
Properties of Fresh concrete:
Workability reduces at higher dosage of fibres
compared to initial dosage used. Vee-bee time
indicates that for control concrete and at 0.5% of fibre
content workability is high. Workability at1% is
medium. Due to more addition of fibres, there is
increase in amount of entrapped air voids due to
presence of fibres and therefore increase in air content
attributes in reducing workability and difficulty is
observed in compaction of mixes. The fibres may also
cause a finishing problem.

Fig. 2. Vee-bee time at Different Fibre Content
Compressive Strength
In general, the improvement in cube strength observed
in commonly used mixes due to fibre addition is small.
The addition of polypropylene fibres to the mix
increased the 28 day’s compressive strength of the mix
with the dosage of 1.5% by 16% due the confinement
provided by fibres. The compressive strength at 1.5%
dosage is slightly higher than strength at 2% dosage.
Compressive strength increases for all dosage of fibres
than normal concrete Reason is that due to confinement
provided by fibre bonding characteristics of concrete
increases and hence compressive strength increases
with the increases in the fibre content.

Fig. 3. Compressive Strength at Different Fibre
Content
Split Tensile Strength
The split tensile strength varies from 3 MPa to 4.25
MPa for 7 days and 7.48 MPa to 9.2 MPa for 28 days.
Test results shows maximum 23% increases in split
tensile strength at 28 days. Split tensile test does not
give perfect estimation about direct tensile strength due
to mixed stress field and fibre orientation but its failure
pattern gives good idea about ductility of the material.
Failure patterns of splitting tensile test indicate that
specimens after first cracking do not separate unlike
the concrete failure. Large damage zone is produced
due to closely spaced micro cracks surrounding a
splitting plane. Fibre bridging mechanism is
responsible for such enhanced ductile failure patter.

Fig. 4. Split Tensile Strength at Different Fibre
Content
International Journal of Advanced Engineering Technology
E-ISSN 0976-3945

IJAET/Vol.III/ Issue I/January-March, 2012/42-45




Flexural Strength
The flexural strength of the mix with the dosage of
0.5% and 2% are increased by 16% and 36%
respectively. Nominal increases remains for all dosage
of fibres compared to normal mixes. The enhancement
in flexural strength is achieved due to the improvement
in mechanical bond between the cement paste and
fibre. As amount of fibre increases in mix, it greatly
helps to reduce widening of crack more effectively,
thus resulting in increase in flexural strength.

Fig. 5. Flexural Strength at Different Fibre Content
Shear Strength
The addition of polypropylene fibers to the mix
increased the shear strength of the mix with the dosage
of 0.5% and 2% by 23% and 47% respectively. A fibre
reduces the crack spacing, thus indicating a more
redistribution of stresses. As the first crack forms, the
fibres bridge it, transmitting stresses across the crack
surface. In order to enforce further crack opening the
applied load has to be increased, which leads to the
formation of another crack. This mechanism then
repeats until failure.

Fig. 6. Shear Strength at Different Fibre Content
Load-Deflection Curve:
The load-deflection curve for polypropylene FRC with
high fibre volume fraction was elastic-plastic with a
transition zone. No significant drop in the load was
observed after first crack. The specimen shows large
numbers of fine cracks before failure. After cracking,
the fibres play major role in deformation. It was
observed that the performance of both concrete types
(with and without fibres) is very similar until first crack
load is reached. The curve for concrete without fibre
finished when the specimen showed the first crack.
However, PFRC allows much higher strain and is able
to resist increasing loads after the first crack.

Fig.7. Load v/s deflection for flexure at different
fiber content
CONCLUSIONS:
• Polypropylene fibres dose not disperse properly
in the mixing water. Addition of fibres to dry mix
was found to be more practical.
• The presence of fibres in concrete alerts the failure
mode of material. It is found that the failure mode
of plain concrete is mainly due to spalling, while
the failure mode of fibre concrete is bulging in
transverse directions.
• Compressive strength of material increases with
increasing fibre content. Strength enhancement
ranges from 8% to 16% for PFRC.
• Strength enhancement in splitting tensile strength
due to polypropylene fibre addition varies from
5% to 23%. Split tensile strength at 28’days is
approximately 50% higher than 7 day’s strength.
• During the test it was visually observed that the
PFRC specimen has grater crack control as
demonstrated by reduction in crack widths and
crack spacing. The flexural strength increases with
increasing fibre content. The maximum increase in
flexural strength of PFRC is 36%.
• The percentage increase in shear strength of the
polypropylene fibre mix varies from 23% to 47%.
This is because of fibres enhances the load
carrying capacity of mix.
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International Journal of Advanced Engineering Technology
E-ISSN 0976-3945

IJAET/Vol.III/ Issue I/January-March, 2012/42-45




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