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FIBRE REINFORCED CONCRETE:
 Plain concrete possesses a very low tensile strength, limited to ductility and little
resistance to cracking.
 Internal micro-cracks are inherently present in the concrete and its poor tensile
strength is due to the propagation of such micro-cracks, eventually leading to the
brittle failure of the concrete.
 It has been recognized that the addition of small, closely spaced and uniformly
dispersed fibres to concrete would act as crack arrester and would substantially
improve its static and dynamic properties.
 Fibre Reinforced Concrete is therefore defined as the concrete made with cement,
containing fine or fine and coarse aggregate and discontinuous discrete fibres.
 The fibres can be made from
 Natural Material . :- Such as Asbestos, Sisal, & Cellulose
 Manufactured Products :- Such as Glass, Steel, Carbon, & Polymer (e.g. Polypropylene,
Nylon etc.)
 Fibre reinforcement improves the impact and fatigue strength, and reduces the
shrinkage.
 Fibre is a small piece of reinforcing material possessing certain characteristic
properties.
 They can be circular or flat.

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 The quantity of fibre used is small, typically 1 to 5 percent by volume.
 To render them effective as reinforcement:
– The tensile strength
– Elongation at failure, and
– Modulus of elasticity
of the fibres need to be substantially higher than the corresponding properties of the matrix.
 Some other significant characteristics of the fibres are:
– Aspect Ratio (ratio of length to mean diameter)
– Shape and surface texture
– Length and
– Length and
 The fibre can withstand a maximum stress f, which depends on the aspect ratio
(L/D), Viz.:
(1)
Where,  = Interfacial bond strength
d = Mean diameter of fibre
L = Length of fibre (L<LC).
)
d
L
(

 
f

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 LC is the critical length of the fibre such that,
If L < LC
the fibre will pull out of the matrix due to failure of bond, and
If L>LC then,
the fibre itself will fail in tension.
 The length of the fibre should be greater than the maximum size of the aggregate
particles.
 According to Eq.(1), the higher the interfacial bond strength the higher the
maximum stress in the fibre.
 The interfacial bond strength is improved by fibres having:
 A deformed or roughened surface,
 Enlarged or hooked ends, and
 By being crimped.
 The type of fibres used may be of Steel, Polypropylene or Nylon, Asbestos, Glass
and Carbon.

4. Steel Fibres:-
 It is one of the most commonly used fibres.
 Generally round fibres with a diameter ranging from 0.25 to 0.75 mm are
used.
 Use of steel fibres makes significant improvements in flexural, impact and
fatigue strength of concrete.
 It has been extensively used in various types of structures Such as :
 Overlaying of Roads
 Airfield Pavements and
 Bridge Decks
 Thin Shells and Plates have also been constructed using steel fibres.
Polypropylene And Nylon Fibres:-
 They are found to increase the impact strength.
 They possesses very high Tensile Strength.
 Their low Modulus of Elasticity and higher Elongation do not contribute to the
flexural strength.
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5. Asbestos Fibres:-
 It is a mineral fibre and has proved to be most successful of all fibres, and can
be mixed with Portland cement.
 Tensile strength varies from 5600 to 9800 Kg/cm2
Glass Fibres:-
 Glass fibres are the recent introduction in making fibre concrete.
 It has a very high tensile strength varying from 10200 to 40800 Kg/cm2
 Glass fibre was fund to be affected by alkaline condition of cement, therefore
alkali-resistant glass fibre by the trade name of “CEM-FIL” has been
developed and used.
 The alkali resistant glass fibre reinforced concrete shows considerable
improvement in durability when compared to the conventional glass fibre
concrete.
Carbon Fibres:-
 Carbon fibres, perhaps possesses very high tensile strength (21120 to 28150
Kg/cm2) and Young’s modulus.
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6.  It has been reported that cement composite made with carbon fibre as
reinforcement will have very high modulus of elasticity and flexural strength
and good durability.
Properties & Applications
 It has been increasingly used on account of increased
 Static and dynamic tensile strength,
 Energy absorbing characteristics and
 Better fatigue strength.
 The uniform dispersion of fibres throughout concrete provides isotopic
properties not common to conventional reinforced concrete.
 It has been tried on:
 Overlays of airfield
 Road pavements
 Industrial floorings
 Bridge decks
 Canal linings
 Explosive resistant structures
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7.  The FRC can also be used for the fabrication of pre-cast products like pipes,
boats, beams, stair case steps, wall panels, roof panels, manhole covers etc.
 The FRC sometimes called fibrous concrete, is manufactured under the trade
name “Wirand Concrete”, and after extensive research has been extensively
used in USA.
 With the development of ‘CEM-FIL’ the alkali resistant glass fibre by the U.K.
Building Research Establishment and Pilkington Glass, UK, a wide ranging
applications of fibrous concrete is being made in various areas of building
construction.
 Glass reinforced cement consist of 4 to 4.5 per cent by volume of glass fibre
mixed into cement or cement sand mortar.
 This glass reinforced cement mortar is used for fabricating concrete products
having a section of 3 to 12 mm in thickness.
 The GRC has been used for cladding of buildings, temporary or permanent
form-work, pressure pipes, door and door frames decorative grills, sun
breakers, bus shelters, and park benches etc.
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