Fibers can be metallic (steel), mineral (asbestos or glass) or natural or synthetic organic (polypropylene, aramid or sisal). They can be incorporated in concrete by premixing, by shotcreting or by spraying. New types of fibers, new methods of fabrication and different types of applications are continuously being developed.
Asbestos is a naturally available mineral fiber. It has been successfully combined with portland cement paste to form the product called asbestos cement. Asbestos cement has been the most widely used fiber- reinforced concrete composite.
Glass fibers are used in large quantities with resin matrix in the production of fiberglass composites. The common glass fibers called E glass are believed to be chemically attacked by the highly alkaline environment of cement paste, and as a result, the glass-fiber- reinforced cement composites lose their strength with time. The strength reduction depends on the chemical nature of the glass and the cement paste as well as the environment.
Steel wire is produced by a series of hot and cold working methods. Round steel fibers are produced by cutting or chopping the wire, typically having diameters in the range of 0.01 to 0.03 inch.6.
Organic fibers include synthetics such as polypropylene or natural fibers such as sisal. Organic fibers are lighter in weight and may be more chemically inert than either steel or glass fibers. They also may be more economical, especially if they are natural. However, these fibers produce lower bond and a lower modulus of elasticity than mineral or metallic fibers