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Topic – Fiber-reinforced Concrete
Introduction
Concrete
Concrete is one of the most widely used building materials. The reasons for its popularity include moldability, easy availability of raw materials, strength, economy and durability. In spite of many advantages like high compressive strength, concrete is not devoid of flaws. Few of which are low tensile strength, low toughness, shrinkage, proneness to cracking and presence of voids. To overcome the problem of low tensile strength, steel and fiber reinforcing bars are introduced in the tensile sections. This material is popularly known as Reinforced Cement Concrete (RCC). In few cases, reinforcing is also provided in compression zones which help in reducing the size of the sections. Concrete being a brittle material and does not undergo inelastic deformations. It fails suddenly with little or no indication or signs of failure. Introduction of rebars takes up the tensile forces and enhances the ductility. But it does not offer a complete solution to all the problems, a special of concrete by the name Fiber Reinforced Concrete (FRC) was introduced in 1950s. Prior to that, usage of fibers like horse hair, straw has been practiced in ancient Roman structures and asbestos fibers were used in early part of the 19th century.
Fiber reinforced concrete
FRC is a composite material consisting of cement, aggregate, water in which discrete, non-continuous fibers are randomly distributed and oriented in all directions of the concrete matrix. Continuous meshes, woven fabrics and long wires or rods are not considered to be discrete fibers.Steel or fiber rebars can also be additionally used to satisfy the minimum reinforcement norms of the local authorities.
Figure 1 Fiber concrete
Definition of FRC by ACI
Fiber-reinforced concrete (FRC) is concrete made primarily of hydraulic cements, aggregates, and discrete reinforcing fibers. Fibers suitable for reinforcing concrete have been produced from steel, glass, and organic polymers (synthetic fibers). Naturally occurring asbestos fibers and vegetable fibers, such as sisal and jute, are also used for reinforcement. The concrete bases may be mortars, normally proportioned mixtures, or mixtures specifically formulated for a particular application. If properly engineered, one of the greatest benefits to be gained by using fiber reinforcement is improved long-term serviceability of the structure or product.1
Fibre-reinforced Concrete – A detailed discussion
FRC can be used in all situations where RCC is used. Its applications include pavements, roofing elements, foundations, and various otherstructural components of building, precast elements, shortcrete, rehabilitation of structures etc. From research, it has been established that the fibers enhance the cohesiveness, structural integrity, tensile strength, toughness and elastic properties. Moreover, they are helpful in bringing down the deflection of the elements and reduce cracking caused due to plastic and drying shrinkage and due to load, as well. The effect of randomly dispersed fibers in reduction of propagation of fibers and a comparison of the cracking pattern in concrete with and without fibres are demonstrated in figure 2.
Figure2. Effect of fibers in reducing the propagation of cracks
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