Fibre
reinforced concrete (FRC) may be defined as a composite materials made with
Portland cement, aggregate, and incorporating discrete discontinuous fibres.
Plain unreinforced concrete is a brittle material, with a low tensile strength
and a low strain capacity. The role of randomly distributes discontinuous
fibres is to bridge across the cracks that develop provides some post-cracking
ductility. If the fibres are sufficiently strong, sufficiently bonded to
material, and permit the FRC to carry significant stresses over a relatively
large strain capacity in the post-cracking stage.
There are
other ways of increasing the strength of concrete. The real contribution of the
fibres is to increase the toughness of the concrete (defined under the load vs.
deflection curve), under any type of loading. That is, the fibres tend to
increase the strain at peak load, and provide a great deal of energy absorption
in post-peak portion of the load vs. deflection curve.
When the
fibre reinforcement is in the form of short discrete fibres, they act
effectively as rigid inclusions in the concrete matrix. Physically, they have
thus the same order of magnitude as aggregate inclusions; steel fibre
reinforcement cannot therefore be regarded as a direct replacement of
longitudinal reinforcement in reinforced and prestressed structural members.
However, because of the inherent material properties of fibre concrete, the
presence of fibres in the body of the concrete or the provision of a tensile
skin of fibre concrete can be expected to improve the resistance of
conventionally reinforced structural members to cracking, deflection and other
serviceability conditions.
The fibre
reinforcement may be used in the form of three – dimensionally randomly
distributed fibres throughout the structural member when the added advantages
of the fibre to shear resistance and crack control can be further utilised . On
the other hand, the fibre concrete may also be used as a tensile skin to cover
the steel reinforcement when a more efficient two – dimensional orientation of
the fibres could be obtained.
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