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ABSTRACT
In conventional concrete, micro-cracks develop before structure is loaded because of drying shrinkage and other
causes of volume change. When the structure is loaded, the micro cracks open up and propagate because of
development of such micro-cracks, results in inelastic deformation in concrete. Fibre reinforced concrete (FRC)
is cementing concrete reinforced mixture with more or less randomly distributed small fibres. In the FRC, a
numbers of small fibres are dispersed and distributed randomly in the concrete at the time of mixing, and thus
improve concrete properties in all directions. The fibers help to transfer load to the internal micro cracks. FRC is
cement based composite material that has been developed in recent years. It has been successfully used in
construction with its excellent flexural-tensile strength, resistance to spitting, impact resistance and excellent
permeability and frost resistance. It is an effective way to increase toughness, shock resistance and resistance to
plastic shrinkage cracking of the mortar. These fibers have many benefits. Steel fibers can improve the structural
strength to reduce in the heavy steel reinforcement requirement. Freeze thaw resistance of the concrete is
improved. Durability of the concrete is improved to reduce in the crack widths. Polypropylene and Nylon fibers
are used to improve the impact resistance. Many developments have been made in the fiber reinforced concrete
INTRODUCTION
Concrete made from Portland cement, is
relatively strong in compression but weak in
tensionand tends to be brittle(Banthia N (2012)
.The
weakness in tension can be overcome by the use of
conventional steel bars reinforcement and to some
extent by the mixing of a sufficient volume of certain
fibers. The use of fibers also recalibrates the behavior
of the fiber-matrix composite after it has cracked
through improving its toughness (Nataraja M.C., Dhang
N)
.This thesis is aims to provide information on the
properties and applications of the more commonly
available fibers and their uses to produce concrete
with certain characteristics. A new kind of fibre
reinforced concrete is developed which is made from
cellulose fibers.
A fibre is a small discrete reinforcing
material produced from various materials like steel,
plastic, glass, carbon and natural materials in various
shapes and size(ACI Committee 440. 1996)
.
A numerical parameter describing a fibre as
its aspect ratio, which is defined as the fibre length,
divided by an equivalent fibre diameter [l/d].Typical
aspect ratio[l/d] range from 30 to 150 for length
dimensions of 0.1 to 7.62 cm typical fibre diameters
are 0.25 to 0.76 mm for steel and 0.02 to 0.5 mm for
plastic.
The plain concrete fails suddenly when the
deflection corresponding to the ultimate flexural
strength is exceeded, on the other hand fiberreinforced
concrete continue to sustain considerable
loads even at deflections considerably in excess of
the fracture deflection of the plain concrete.
1.0FIBER REINFORCED CONCRETE –
1.1 STEEL FIBER REINFORCED CONCRETEteel
fibre reinforce concrete is a composite material
which is made up from cement concrete mix and steel
fibres as a reinforcing. The steel fibres, which are
uniformly distributed in the cementations mix .This
mix, have various volume fractions, geometries,
orientations and material properties. It has been
shown in the research that fibres with low volume
fractions (<1%), in fibre reinforced concrete, have an
insignificant effect on both the compressive and
tensile strength.
POLYMER FIBER REINFORCED
CONCRETE:-Civil structures made of steel
reinforced concrete normally suffer from corrosion of
the steel by the salt, which results in the failure of
those structures. Constant maintenance and repairing
is needed to enhance the life cycle of those civil
structures.
There are many ways to minimize the failure
of the concrete structures made of steel reinforce
concrete. The custom approach is to adhesively bond
A uniform distribution of fibers throughout
the concrete improves the homogeneity of the
concrete matrix. It also facilitates reduced water
absorption, greater impact resistance, enhanced
flexural strength and tensile strength of concrete. The
use of polymer fibers with concrete has been
recognized by the Bureau of Indian Standards (BIS)
and Indian Road Congress and is included in the
following Standard documents:-
IS: 456:2000 – Amendment No.7, 2007
IRC: 44-2008 – Cement Concrete Mix Designs for
Pavements with fibers
IRC: SP: 76:2008 – Guidelines for Ultra-Thin White
Topping with fibersVision: 2021 by Ministry of
Surface Transport, New Delhi
Polymer Fibre Reinforced concrete has been
approved by National bodies like:-
* Central Public Works Department (CPWD)
Specification for Concrete Aggregates -
Water and admixtures - The water to be used for
the mix should be clean and of good quality.
Admixtures such as accelerating agents may be used
in order to decrease the influence of the glucose
retardant.
Fibres - The length of fibers may vary from 1 to 2 in.
(25 to 500 mm). Because natural fibers are naturally
available materials, they are not uniform in diameter
and length. Typical values of diameter for
unprocessed natural fibres vary from 0.004 to 0.03 in.
(0.10 to 0.75 mm).
Methods of mixing- The two methods of mixing and
placing are:-
1.Wet mix
2. Dry-compacted mix.
In the wet mix, a low volume fraction of fibres is
used. The water to be added to the mix has to take
into account the high natural water content in the
natural fibers
1.5 SYNTHETIC FIBRE-Synthetic fibres are no
substitute for primary reinforcement in concrete
because they add little or no strength. But structural
reinforcement doesn‟t provide its benefits until
concrete hardens. That‟s why some contractors add
synthetic fiber to concrete as secondary. Unlike
structural reinforcement, synthetic fibers
providebenefits while concrete are still plastic. They
also enhance some of the properties of hardened
concrete.
1.5.1 Synthetic fibres types- The number of
synthetic fibre has grown in recent years, the primary
types of synthetic fibres commercially available in
the India are polypropylene, polyester, and nylon.
Though the fibres within each type come in various
lengths, thicknesses, and geometries, synthetic fibres
provide similar benefits when used as secondary
concrete reinforcement.
Polypropylene- The synthetic fibers available in the
United States, polypropylene is the most widely used
in ready mixed concrete .Polypropylene fibers are
hydrophobic, so they don‟t absorb water and have
no effect on concrete mixing water requirements.
They come as monofilaments.
Polyester- Though not as widely used as
polypropylene fibers, polyester fibers are offered by
several manufacturers. The fiber bundles come only in monofilament form in lengths from 0.75 to 2
inches.
Nylon- Like poly-ester fibres, nylon fibres come only
in monofilament form. What primarily distinguishes
them from polypropylene and polyester fibers is their
hydrophilic nature. Nylon fibre manufacturers also
report that their fibres have higher aspect ratios (ratio
of length to diameter) than those made of
polypropylene. Therefore, they can be added in
smaller dosages to produce the same reinforcing
effects. Usually no more than 1 pound per cubic yard
is needed.
Mixing - Fibres can be added with the coarse and
fine aggregate at the batch plant or to the central or
truck mixer at the jobsite. If adding the fibers with
other mix ingredients, no extra mixing time is
needed. If adding the fibers to mixed concrete, agitate
the concrete an additional 3 to 7 to disperse the fibers
thoroughly.
II. Mechanical Properties of FRC-
2.1 COMPRESSIONThe
presence of fibers may alter the failure mode of
cylinders, but the fiber effect will be minor on the
improvement of compressive strength values (0 to 15
%).
STEEL FIBER-The presence of fibers may alter the
failure mode of concrete, but the fibers effect will be
minor on the improvement of compressive strength
values (0 to 15 percent).
The strain of SFRC corresponding to peak
compressive strength increases as the volume fraction
of fibers increases. As aspect ratio increases, the
compressive strength of SFRC also increases
marginally.
As the load increases, the deflection also increases.
However the area under the load–deflection curve
also increases substantially depending on the type
and amount of fibers added.
GLASS FIBER – Glass fibers mixed thoroughly
mixed in the composition and filled in the Steel
mould of size 150 x 150 x 150 mm is well tighten
and oiled thoroughly. They were allowed for curing
in a curing tank for 28 days and they were tested in
200-tonnes electro hydraulic closed loop machine.
The test procedures were used as per IS: 516-
1979[16].
POLYMER FIBER - Compressive strength is
essentially matrix dependent.In-plane (“edgewise”)
compressive strength will be somewhat lower than
cross-plane strength due to the layers of glass fibers affecting the continuity of the matrix. Cross-plane
compressive strength (“flatwise”) is not influenced
by the presence of glass fibers and will be about the
same as the compressive strength measured on bulk
matrix materials in cube or cylinder tests
NATURAL FIBERS- The cubes tests prepared with
different fibers, different fibers volumetric ratios and
different reductions in coarse aggregate, showed
large variations in the test results as compared to the
control specimens with no fibers. The variation in the
results could be attributed to the relatively small size
of the cube which may result in erroneous data
compared with 15x30 cm standard cylinders.
SYNTHETIC FIBERS - The compressive strength
of concrete is one of the most important and useful
properties of concrete. In most structural applications
concrete is used primarily to resist compressive
stress. The compression test was conducted on cube
specimens cured for 7, 14 & 28 days. The test cubes
were removed from the moist storage 24 hours before
testing. The top and bottom bearing plates of the
compression testing machine were wiped and cleaned
before the placement of the specimen.
2.2 MODULUS OF ELASTICITY – Modulus of
elasticity of FRC increases slightly with an increase
in the fibers content. It was found that for each 1
percent increase in fiber content by volume there is
an increase of 3 percent in the modulus of elasticity.
STEEL - The main parameters that characterise the
compressive behaviour of concrete are the slope of
the ascending branch (Young's modulus),the
compressive strength, and the strain at peak stress.
These parameters were determined from the
respective average curve for each composite.