FIBER REINFORCED CONCRETE

               Fiber reinforced concrete is the most widely using technology since early days. It is a technique of adding single type fiber or a blend of fiber to the mixture of concrete. Steel fibers and synthetic fibers can be added to the mixture which adds the mechanical properties of concrete. Concrete which is compared to other building structure is more brittle and it has poor tensile strength. As concrete is subjected to cracks, fibers are adding to it to get the strength. Mostly used fibers for reinforcement are natural fibers, synthetic fibers, steel fibers and glass fibers. 

Advantages of Fiber Reinforced Concrete

·         It controls cracking of concrete

·         Reduce permeability of concrete and thus reduce water bleeding

·         Higher the modulus elasticity of the fiber, higher will be the loading capacity of material.

Fiber Reinforced composites

Fiber reinforced composites consists of fibers and a matrix. Fibers are the main source of strength. And the matrix is used to bind fibers together in shape and transfers stresses between the fibers. It protects fibers from mechanical as well as external damages. 

·    Matrix - Matrix should be such that its strain at break must be larger than the fibers it carries. Commonly matrix is made up of resins. Widely used resin is polyesters. Metal matrices are also used where higher performance at elevated temperature requires. 

·    Modifiers - Modifiers and fillers are the additives which added to smooth manufacturing process, impart special properties, or reduce product cost. Commonly used modifiers are Benzoyl peroxide, Tertiary butyl catechol, Dimethyl aniline, Zinc stearate, waxes, silicones, etc.

Different types of fiber reinforced concrete are discussed below.

·       Natural Fiber reinforced concrete (NFRC)

                       In NFRC, naturally occurred fibers are used for reinforcement. Natural fibers can be obtained at low levels of cost and energy. Best known natural fibers are sisal, coir, bamboo, jute, akwara, and elephant grass. They are called unprocessed natural fibers.  Wood fibers are also used by processing it. They are obtained from Kraft processing (chemical processing). Since it is obtained from processing, it is known as processed natural fiber (PNF).

                                Properties of natural fibers

·         Sisal : This fiber has been used for making gypsum plaster sheets in Australia. It is stronger enough than many other natural fibers.

·      Coir : it is obtained from the hard outer cover of the coconut. It is resistant to natural weathering and increases the modulus of rupture of concrete.

·         Bamboo : It is widely available in tropic and sub-tropical regions. And it belongs to grass family. It is strong in tension. Special equipment is needed for the extraction of fibers from Bamboo stem.

·         Jute : Jute is mainly seen in India, Bangladesh, China and Thailand. It is a commonly used fiber for making ropes and bags. It can be used in cement matrix due to its strong tension.

·       Synthetic Fiber reinforced concrete (SFRC)

                  Synthetic fibers are manufactured from materials such as acrylic, aramid, carbon, nylon, polyester, polyethylene, or polypropylene. The most commonly used synthetic fibers in concrete pavements are made of fibrillated polypropylene. The benefits of polypropylene fibers included reduced plastic shrinkage and subsidence cracking. They have a low modulus of elasticity, varying between 3 and 5 GPa. Available polypropylene fibers are typically short in length and small in diameter.

                        Recently another type of synthetic fiber has become available for structural applications called macro-synthetic fiber. Compared to the polypropylene fibers, these macro-synthetics are larger in length and diameter, and have a higher modulus of elasticity.

·       Steel fiber reinforced concrete

                               Steel fibers have a high modulus of elasticity (200 GPz) and a high resistance in traction (between 800 and 2,500 MPa). The most common applications are pavements, tunnel linings, pavements and slabs, airport pavements, bridge deck slab repairs, and so on. When used in structural applications, steel fibre reinforced concrete should only be used to inhibit cracking, to improve resistance to impact or dynamic loading, and to resist material disintegration.

·       Glass fiber reinforced concrete (GFRC)

                               Glass fiber reinforced concrete consists of material that taken from soil and it has no adverse effect on environment. It includes Fly Ash, Silica Sand, Portland cement and aggregate. Since it contains glass fibers instead of steel there is no need of concrete cover thickness to prevent rusting. Main advantages of glass fibers are durability, weather resistant and their superior strength. Moreover it is light weight.