In conventional concrete, micro cracks are developed in concrete due to drying shrinkage and other causes like weather, temperature, insufficient curing, vibrations etc. This cracks are occur even before the loading on the slab. When the structure is loaded, this cracks will open up and start propagate which further damage the slab. The development of such micro cracks is the main reason of inelastic deformation in the concrete.

This cracks makes concrete weaker. To prevent this thing, Closely spaced and uniformly dispersed fibers are added in concrete to make concrete more stronger. This addition of fibers substantially improve the static and dynamic properties of concrete. These fibers offer increased resistance to growth of crack and improves the tensile strength and durability of concrete.

Fiber reinforced concrete (FRC) can be defined as composite material consisting of concrete and uniform dispersed fine fibers. The continuous meshes, woven fabrics and long wires are not considered as discrete fibers.

Types of fibers used in Fiber reinforced concrete.

Fiber is a small discrete reinforcing material produced from various materials like steel, polypropylene, plastic/nylon, glass, asbestos, carbon or organic matters in various shape and size. They can be circular or flat. An important considerable parameter about fiber is its aspect ratio which is defined as the length of fiber to the diameter of the fiber. Typical aspect ratio is 30 to 150 for length dimensions 0.1 to 7.62 cm.

1. Steel fibers
Steel fiber is one of the most commonly used fiber. They are generally round. The diameter of steel is vary from 0.25 mm to 0.75 mm. The steel fiber is likely to get rusted and lose some of its strength. Use of steel fibers significant improves flexural impact strength and fatigue strength of concrete.

Steel fiber is extensively used in roads, pavements, air fields, bridges and flooring subjected to wear and tear and chemical attack.

Deformed steel fibers are most commonly suggested to use. Since individual fibers tens to cluster together, their uniform distribution is often difficult. Steel fibers decrease the woorkability of concrete.

2. Glass fiber
These are produced in three basic forms.
A. Rovings
B. Strands
C. Woven

Glass fibres are Continuous filament and alkali resistant fibres. Glass fibers of 10mm to 50mm in length and a few microns in diameter can be added up to 5% by weight and premixed with cement and water in a pan or a paddle mixer. 
Small quantities of lubricating admixtures, such as polyethylene oxide or methyl cellulose may be added into the mix. The resulting mix may be sprayed or cast into the moulds.

The products can also be produced either by extrusion or by injection-moulded process. In some of the processes, rovings can be chopped in-situ and sprayed simultaneously with a slurry of suitable consistency on a mould of production. 

GFRC is significantly more environmentally friendly than traditional concrete, making use of recycled materials and requiring less cement. 

Strength of GFRC is developed due to high contents of alkali resistant glass fibers and acrylic polymer. Since the cement contents are high, and the ratio of water to cement is low, the GFRC strength under compressive loads is high. GFRC also possesses great tensile and flexural strength. 

Glass fiber concretes are mainly used in exterior building fa├žade panels and as architectural precast concrete. GFRC is also used extensively for decorative panels.

3. Plastic fibers
Fibers such as nylon, acrylic, polypropylene, polyethylene are know as plastic fibers. They have high tensile strength but low young's modulus thus inhibiting reinforce effect.

Polypropylene and nylon fibers are found to be suitable to increase the impact strength. Their addition to concrete has shown better distribute cracking and reduced crack size. They have low modulus of elasticity. The amount of plastic fibers added to concrete is about 0.25 to 1 percent by volume. The polypropylene fibers are available in two forms, mono filaments and film fibers. The film fibers are commonly used.

4. Asbestos fibers
Asbestos is a mineral fiber and has proved to be the most successful fiber, which can be mixed with OPC. The maximum length of asbestos fiber is 10 mm but generally fibers are shorter than this. The composite has high flexural strength. Tensile strength of asbestos varies between 500 to 980 N/mm². It has low specific gravity around 2.55 Hence it makes concrete light compare to steel fibers.

5. Carbon fibers
Carbon fibers possess high tensile strength and high young's modulus. The modulus of rupture of an aligned carbon fiber reinforced cement composite with 8 percent fiber volume can be high as 1623 N/mm². The use of carbon fibers in concrete is promising but it is costly and availability of carbon fibers is limited.

Advantages of FRC
1. Reduction in shrinkage and cracking.
2. Improve in bond strength.
3. Enhancement of fatigue strength and endurance limit.
4. Better toughness.
5. Lower permeability of concrete.

Application of FRC

1. The most extensive use of FRC has been for pavements, floors and overlays to take advantage of increased strength. redced crack and thickness reduction.

2. Overhead water tanks and underground sumps needs to be watertight. Fibers contribute to control plastic shrinkage cracks and resulting in watertightness.

3. The FRC can also be used for the fabrication of precast products like pipes, boats, beams, wall panels, staircase steps, roof panels, manhole covers etc.

4. FRC has been used a swearing surface to existing bridges and culverts in area specially troubled by degradation caused through abrasion by studded tyres.

5. FRC is cohesive and easy to work provided fibers are throughly mixed in cement matrix. It is an ideal material for repair and rehabilitation work.


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