Fibre Reinforced Concrete
What Is Fibre Reinforced Concrete?
Fibre reinforced concrete is a special type of concrete made up of cement, aggregates, and a certain amount of fibres.
Fibres are used to reduce permeability, bleeding, and the formation of minor cracks in concrete. Fibres also improve the tensile strength and impact resistance of concrete.
The improvement of weakness depends on several factors such as materials of fibre, shape, and size of fibre, volume, and pattern of distribution in the concrete mix. Different types of fibres like steel fibres, glass fibres, asbestos fibres, polypropylene fibres, carbon fibres, and organic fibres are used in concrete. Fibre reinforced concrete can be categorized into the following two types.
1. Steel Fibre Reinforced Concrete.
2. Glass Fibre Reinforced Concrete.
1. Steel Fibre Reinforced Concrete:
Steel Fibre Reinforced Concrete or SFRC is produced by mixing little amount of steel fibres in the elements of concrete. Steel fibres are regularly prepared by cutting 10-60 mm length of low carbon steel wires diameter of 0.25-0.75 mm.
Other than round fibers, flat steel fibres are moreover normal in use. Flat sheet steel fibers are prepared by cutting 0.15-0.40 mm thick plates in widths extending from 0.25-0.90 mm, furthermore length 10-60 mm.
Steel fibers tend to cluster together which creates difficulties in ensuring their uniform random distribution in the concrete. This problem is overcome by using fiber bundles. The steel fibre in the fibre bundles separates out at the time of concrete mixing and gets distributed randomly in the concrete mix.
By adding 2 – 3% fibers (by volume) it is possible to achieve two to three times increase in the flexural strength of the concrete and furthermore increase in crack resistance, explosion resistance, and different properties of the concrete.
SFRC is suitably used in the construction of pavements, bridge decks, pressure vessels, tunnel lining, etc.
2. Glass Fibre Reinforced Concrete:
Glass fibers are normally produced from 200 – 400 different filaments that are lightly bonded to create a strand. These strands are sheared into different lengths for making cloth, mat, and tape. It is possible to improve the tensile strength and impact resistance two times by adding 10% fibreglass in the concrete.
By using the conventional mixing method only 2% fibres can be mixed in 25 mm length. It is found that the strength of glass fibre significantly increases as its diameter is reduced. Small diameter glass fibres are strong in tension but also very brittle. That’s why they can not be used in longer spans.
Glass fibres get corroded due to the effect of alkali present in the portland cement. To use glass fibres as micro reinforcement they need to be properly treated (epoxy resin coating).
Glass Fibre reinforced concrete is mostly used for manufacturing precast products such as spun pipes, wall cladding etc.
Advantages Of Fibre Reinforced Concrete:
1. High tensile strength and impact resistance to fatigue stresses and thermal shocks.
2. Increased durability.
3. High flexural rigidity.
4. Reduced permeability, bleeding, and formation of micro cracks.
5. Minimum weathering effect.
6. Reduces deflection.
7. Minimum corrosion.
Disadvantages Of Fibre Reinforced Concrete:
1. Fibres are costly.
2. The fibres should be uniformly distributed in concrete because they may not mix well and form lumps.
3. The size of the coarse aggregate is restricted to 10 mm.
4. Mixing of fibres in large volumes could be tedious.
5. Construction with FRC requires skilled labours.
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