Fiber Reinforced Concrete - Types: 1. GFRC, 2. Steel

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What Is Fibre Reinforced Concrete?

Fibre reinforced concrete is a special type of concrete made up of cement, aggregates, and a certain amount of fibers.

Fibers are used to reduce permeability, bleeding, and the formation of minor cracks in concrete. Fibers also improve the tensile strength and impact resistance of concrete.

The improvement of weakness depends on several factors such as materials of fiber, shape, and size of fiber, volume, and pattern of distribution in the concrete mix.

Different types of fibers like steel fibers, glass fibers, asbestos fibers, polypropylene fibers, carbon fibers, and organic fibers are used in concrete. Fiber-reinforced concrete can be categorized into the following two types.

Steel Fibre Reinforced Concrete.
Glass Fibre Reinforced Concrete.

1. Steel Fibre Reinforced Concrete

Steel Fibre Reinforced Concrete or SFRC is produced by mixing a little amount of steel fibers in the elements of concrete. Steel fibers 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 fibers 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 lengths of 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 fiber in the fiber 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 a 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.

Uses

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% fiberglass to the concrete.

By using the conventional mixing method only 2% of fibers can be mixed in 25 mm length. It is found that the strength of glass fiber significantly increases as its diameter is reduced.

Small diameter glass fibers are strong in tension but also very brittle. That’s why they can not be used in longer spans.

Glass fibers get corroded due to the effect of alkali present in the portland cement. To use glass fibers as micro reinforcement they need to be properly treated (epoxy resin coating).

GFRC Uses

Glass Fibre reinforced concrete is mostly used for manufacturing precast products such as spun pipes, wall cladding, etc.

Advantages Of Fibre Reinforced Concrete

High tensile strength and impact resistance to fatigue stresses and thermal shocks.
Reduced permeability, bleeding, and formation of microcracks.
Increased durability.
High flexural rigidity.
Minimum weathering effect.
Reduces deflection.
Minimum corrosion.

Disadvantages Of Fibre Reinforced Concrete

Fibers are costly.
The fibers should be uniformly distributed in concrete because they may not mix well and form lumps.
The size of the coarse aggregate is restricted to 10 mm.
Mixing fibers in large volumes could be tedious.
Construction with FRC requires skilled labor.