IntroductionInfrastructural developments have been at forefront of developing countries. Concrete is an important material being used at greater extend. Modern civil engineering constructions have their own structural and durability requirements related with concrete to suit the intended function of the structure.
Plain concrete has two major deficiencies; a low tensile strength and a low strain at fracture. The tensile strength of concrete is very low because plain concrete normally contains numerous microcracks. It is the rapid propagation of these microcracks under applied stress that is responsible for the low tensile strength of the material. (1)
These deficiencies have lead to considerable research aimed at developing new approaches to modifying the brittle properties of concrete. Current research has developed a new concept to increase the concrete ductility and its energy absorption capacity, as well as to improve overall durability. This new generation technology utilizes discrete steel or synthetic fibres from 19 to 64mm in length. The fibres are randomly dispersed throughout the concrete matrix providing for better distribution of both internal and external stresses by using a three dimensional reinforcing network. General requirements for the fibres used as temperature/moisture, shrinkage reinforcement include: high tensile strength, high bond strength (typically mechanical) and ease to incorporation into the matrix to ensure optimum distribution. The primary role of the fibres in hardened concrete at low volume is to modify the cracking mechanism. By modifying the cracking mechanism, the macro-cracking becomes microcracking. The cracks are smaller in width; thus reducing the permeability of concrete and the ultimate cracking strain of the concrete is enhanced. Unreinforced concrete will separate at a crack, reducing the load carrying ability to zero across the crack. The fibres are capable of carrying a load across the crack, if all of the characteristics listed above are met by the fibres. Fibres reinforced concrete specimens, unlike plain concrete specimens which fail at the point of ultimate flexural strength or the first crack, do not fail immediately after the initiation of the first crack. After first crack, the load is transferred from the concrete matrix to the fibres.
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