PROPERTIES OF FRESH & HARDENED STEEL FIBRE REINFORCED CONCRETE

Abstract

Plain concrete possesses a very low tensile strength, little resistance to cracking and brittle in nature. Internal micro cracks are inherently present in the concrete and due to its poor tensile strength, cracks propagate with the application of load eventually leading to brittle failure of the concrete. The low resistance of concrete to crack propagation results in its low fracture toughness and limited resistance to impact and shock loading. The relatively low tensile strength of concrete has so far been compensated by the use of conventional reinforcing steel bars and also by applying prestressing techniques. In recent yearp, it has been recognised that addition of small closely spaced and uniformly dispersed discrete steel fibres in concrete would substantially improve its static and dynamic properties. The addition of steel fibres from 0.5 to 2.0 percent-by volume in concrete are found to impart superior strength characteristics i.e. compressive strength, flexural strength, shear strength, fatigue strength, impact resistance. The composite matrix possesses• improved ductility and crack resistance. Primarily fibres are a small piece of reinforcing materials such as steel, glass, polymeric and carbon fibres. Fibres can be described by a convenient numerical parameter called "Aspect ratio.", defined as the fibre length divided by diameter. (or equivalent diameter in the case of non round fibres). Effective and efficient use of the fibres in the fibrous concrete depend largely on the uniform dispersion of fibres in the concrete, aspect ratio, volume percentage, size, gradation and quantity of coarse aggregate and water cement ratio. The present investigation was planned to undertake a systematic study of the fresh and hardened state properties of SFRC. The basic parameter of the study were the fibre contents expressed as volume fraction, maximum aggregate sizes and fibre types. iv Fibre contents used were 0.0, 0.5, 1.0, 1.25 and 1.5% by volume of concrete. The maximum aggregate sizes used were 10 mm and 20 mm. Two types of fibres i.e. straight and hooked fibres. used in the investigation. In the fresh state properties of SFRC, workability tests were carried out with indicators of workability i.e. slump, compaction factor and flow table spread. For hardened state properties of SFRC, the tests carried out were compressive strength, flexural strenyth, tensile strenyth, modulus of elasticity, poisson's ratio and impact resistnce.