FIBER REINFORCED CONCRETE - TYPES, APPLICATIONS AND ADVANTAGES

Fiber Reinforced Concrete

Fiber reinforced concrete is a type of concrete containing fibrous materials which increases its structural integrity.It contains short discrete fibers that are uniformly distributed and randomly oriented.Fibers include steel fibers, glass fibers, synthetic fibers and natural fibers.Within these different types of fibers each of them lend varying properties to the concretes, fiber materials, geometries, distribution, orientation and densities.

Effect of Fibers in Concrete

Fibers are usually used in concrete to control cracking due to plastic shrinkage and drying shrinkage.They also reduce the permeability of concrete and thus reduce bleeding of water.Some types of fibers produce greater impact, abrasion and shatter resistance in concrete.Large steeel or synthetic fibers can replace rebar or steel completely in certain situations.Fiber reinforced concrete has all but completely replaced bar in underground construction industry such as tunnel segments where almost all tunnel lining are fiber reinforced in lieu of using rebar.Indeed, some fiber reduce the compressive strength of concrete.

The amount of fiber added to a concrete mix is measured as a percentage of the total volume of the composite (concrete and fibres) termed volume fraction (Vf). Vf typically ranges from 0.1 - 3%.Aspect ratio (l/d) is calculated by dividing fibre length (l) by its diameter (d).Fibers with a non-circular cross section use an equivalent diameter for the calculation of aspect ratio.

Types of Fiber Reinforced Concrete

1. Steel Fiber Reinforced Concrete
2. Glass Fiber Reinforced Concrete - GFRC 
3. Polypropylene Fiber Reinforced Cement Mortar & Concrete
4. Asbestos Fibers
5. Carbon Fibers
6. Organic Fibers

1. Steel Fiber Reinforced Concrete

Steel fiber reinforced concrete has gradually advanced in recent years, rather unproven material to one which has now attained acknowledgement in numerous engineering applications.Lately it has become more frequent to substitute steel reinforcement with steel fiber reinforced concrete.A numbers of steel fiber types are available as reinforcement.Round steel fiber the commonly used type are produced by cutting round wire into short length.The typical diameter lies in the range of 0.25 to 0.75 mm.Rectangular steel fiber are usually 0.25 mm thick, although 0.3 to 0.5 mm wire have been used.

Round steel fibers are produced by cutting or chopping the wire, flat sheet fibers having a typical c/s ranging from 0.15 to 0.41 mm in thickness and 0.25 to 0.90 mm in width are produced by silting flat sheets.Deformed fiber, which are loosely bounded with water-soluble glue in the form of a bundle are also available.

2. Glass Fiber Reinforced Concrete (GFRP)

Glass fiber reinforced concrete consists of high-strength, alkali-resistant glass fiber embedded in a concrete matrix.Glass fiber is made up from 200 to 400 individual filaments that are lightly bounded to make up a stand glass fiber is made and these stands can be combined to make cloth mat or tape or can be chopped into various lengths.It is not possible to mix more than about 2% by volume of fibers of a length of 25mm by using the conventional mixing techniques for normal concrete.

The major appliance of glass fiber has been in reinforcing the cement or mortar matrices used in the production of thin sheet products.The commonly used verities of glass fibers are e-glass used.In the reinforced of plastics & AR glass E-glass has inadequate resistance to alkalis present in Portland cement where AR-glass has improved alkali resistant characteristics.

3. Polypropylene Fiber Reinforced Cement Mortar and Concrete

Polypropylene is one of the cheapest & abundantly available polymers polypropylene fibers are resistant to most chemical & it would be cementitious matrix which would deteriorate first under aggressive chemical attack.Its melting point is high (about 165℃).So that a working temp.

Polypropylene fibers being hydrophobic can be easily mixed as they do not need lengthy contact during mixing and only need to be evenly distressed in the mix.Polypropylene short fibers in small volume fractions between 0.5-15 commercially used in concrete.

4. Asbestos Fibers

Asbestos fibers are naturally available inexpensive mineral fiber,has been successfully combined with Portland cement paste to form a widely used product called asbestos cement.Asbestos fibers are thermal-mechanical & chemical resistance and for sheet product pipes, tiles and corrugated roofing elements these are suitable.The fiber has low impact strength due to a relatively short length of about 10 mm. 

5. Carbon Fiber

Carbon fiber are about 5-10 micrometer in diameter and composed mostly of carbon atoms.Carbon fibers have several advantages including high stiffness, high tensile strength, low weight, high chemical resistance, high temperature tolerance and low thermal expansion.These properties have made carbon fiber very popular.Carbon fiber are expensive and strength and stiffness characteristics have been found to be superior to those of steel.But they are more vulnerable to damage then even glass fiber, and hence are generally treated with resign coating. 

6. Organic Fibers

Organic fiber such as polypropylene or natural fiber may be chemically more inert than steel or glass fibers.They are also cheaper, especially if natural.A large volume of vegetable fiber may be used to obtained a multiple cracking composite.The problem of mixing and uniform dispersion may be solved by adding a superplasticizer.

Application of Fiber Reinforced Concrete

• Pre-cast application
• Fiber shotcrete
• Slope stabilization
• Manholes, roof tiles, panels 
• Dams and hydraulic structures
• Highway and airfield payments
• Impact resisting structures

Advantages of Fiber Reinforced Concrete

• Increase ductility.
• Decrease permeability.
• Increase fire resistance.
• Less prone to corrosion.
• Decrease mix water bleed rate.
• Improve toughness of concrete.
• Greater resistance to crack formation.
• Resistance to thermal and moisture stress.
• Fiber increases the shear capacity of reinforced concrete beam upto 100%.

Disadvantages of Fiber Reinforced Concrete

• Material cost is high.
• Greater reduction of workability.
• Lower compressive strength than steel.
• Cost of forms and artisanry is relatively high.
• Cracks can develop due to shrinkage and live loads.
• Very low tensile power 1/10 of its compressive potency.