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-Concrete is a composite material consisting of mortar and coarse aggregate.An existing problem of concrete is formation of crack.In this study feel fibres are added in concrete to control the concrete 1,1.5,2%of steel fibre is added in concrete, which is the efficient percentage of addition in reinforced concrete. In addition to that to overcome the scarcity of conventional coarse aggregate now-a-days usage of (PET)poly ethylene terephthylate is highly recommended. A conventional method is proposed by using (PET)poly ethylene terephthlate as partial replacement of coarse aggregate to its weight with addition of 1,1.5,2% of steel fibre to the volume of concrete in specimen. Cube of size 150 x 150 x 150 mm is casted and tested, which is designed according to Indian standard codes. The flexural properties of the cube are compared between control specimen and 5%, 10%,15% and 20% partially replaced (PET )poly ethylene terephthalate as coarse aggregate specimens INTRODUCTION:Concrete is known as a brittle material with low bearing capacity for deformation under tensile stress. The development of these tensile stresses are mechanical loading, harmful reactions and environmental loading. Cracks which affect the structural performance of the concrete are caused mainly due to this stress. In order to control the formation of and development of these cracking fibre are introduced in concrete.

The heat transfer characteristics from an isothermal heated plate in a quiescent yield stress fluid in a cavity was investigated over a wide range of parameters (Rayleigh number, 102 ≤ Ra ≤ 105, Prandtl number, 10 ≤ Pr ≤ 100, and Bingham number, Bn ≥ 0) where the flow is known to be laminar and steady. The coupled momentum and energy equations have solved here numerically within the framework of Boussinesq approximation to capture the temperature-dependent fluid density. The results demonstrate that for a given value of the Rayleigh number, there exists a critical value of the Bingham number, above which the fluid is completely unyielded and heat transfer occurs solely by conduction. In order to delineate the effect of domain geometry on the conduction limit, the study was extended over a range of geometrical aspects by varying the aspect ratio (λ = diameter of the cavity/ a length of the plate), 2 ≤ λ ≤ 5. This work shows that the critical value of the Bingham number can be described as a function of geometry of domain, Ra and Pr. The value of critical Bingham number increases with the increasing aspect ratio and Rayleigh number in order to approach the conduction limit. The yield surfaces show that the increasing values of Rayleigh number induce fluid-like behaviour whereas Bingham number opposes this propensity. The average Nusselt number decreases with the increasing Bingham number due to the suppression of the advective component of heat transfer.

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