Abstract :
Fiber
Reinforced Concrete can be defined as a composite material consisting of
mixtures of cement, mortar or concrete and discontinuous, discrete, uniformly
dispersed suitable fibers. Continuous meshes, woven fabrics and long wires or
rods are not considered to be discrete fibers.
Fiber reinforced concrete (FRC) is concrete containing fibrous
material which increases its structural integrity. It contains short discrete
fibers that are uniformly distributed and randomly oriented. Fibers include
steel fibers, glass fibers, synthetic fibers and natural fibers. Within these
different fibers that character of fiber reinforced concrete changes with
varying concretes, fiber materials, geometries, distribution, orientation and
densities.
Fibre-reinforcement is mainly used in shotcrete, but can also be
used in normal concrete. Fibre-reinforced normal concrete are mostly used for
on-ground floors and pavements, but can be considered for a wide range of
construction parts (beams, pliers, foundations etc) either alone or with
hand-tied rebars
Concrete reinforced with fibres (which are usually steel, glass or
“plastic” fibres) is less expensive than hand-tied rebar, while still
increasing the tensile strength many times. Shape, dimension and length of
fibre is important. A thin and short fibre, for example short hair-shaped glass
fibre, will only be effective the first hours after pouring the concrete
(reduces cracking while the concrete is stiffening) but will not increase the
concrete tensile strength
EFFECT
OF FIBRES IN CONCRETE
Fibres
are usually used in concrete to control plastic shrinkage cracking and drying
shrinkage cracking. They also lower the permeability of concrete and thus reduce bleeding of water. Some types of fibres
produce greater impact, abrasion and shatter resistance in concrete. Generally
fibres do not increase the flexural strength of concrete, so it can not replace
moment resisting or structural steel reinforcement. Some fibres reduce the
strength of concrete.
NESSECITY
1 It increases the tensile
strength of the concrete.
2 It reduce the air voids and
water voids the inherent porosity of gel.
3 It increases the durability of
the concrete.
4 Fibres such as graphite and
glass have excellent resistance to creep, while the same is not true for most
resins. Therefore, the orientation and volume of fibres have a significant
influence on the creep performance of rebars/tendons.
5 Reinforced concrete itself is a
composite material, where the reinforcement acts as the strengthening fibre and
the concrete as the matrix. It is therefore imperative that the behavior under
thermal stresses for the two materials be similar so that the differential
deformations of concrete and the reinforcement are minimized.
6 It has been recognized that the
addition of small, closely spaced and uniformly dispersed fibers to concrete
would act as crack arrester and would substantially improve its static and
dynamic properties.
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