Effect of plastic strips on elastic properties of concrete under cyclic loading

Heterogeneous characteristics of concrete with variation in strength of matrix, aggregate and interface causes non-uniform distribution in stress. Reinforcing concrete alters this distribution and can be designed to reduce non-uniformity. Present study investigates applicability of plastic strips as reinforcement to improve performance of concrete. Since plastic strips are strong in tension, they are oriented to control tensile stress generated in concrete. The approach adopted contributed to increment in compressive strength of fibre reinforced concrete. In comparison with conventional concrete, fibre reinforced concrete has higher but delayed compressive strength, lower initial stiffness and higher energy absorption capacity.
In order to assess impact of plastic strips on fundamental properties like Young’s modulus and poisons ratio, cylindrical samples with radially oriented plastic strips are subjected to cyclic loading. Poisson’s ratio is computed by measuring axial and lateral deformation in the sample. To compute Young’s modulus, axial deformation is measured along the gauge length. Response of conventional and fibre reinforced concrete is measured for both loading and unloading cycles considered. In comparison with conventional concrete, fibre reinforced concrete reflects higher axial deformation but the lateral deformation is restrained. This contributes to lower Poisson’s ratio for fibre reinforced concrete. Reduction in lateral deformation of fibre reinforced concrete is an effect of confinement generated by plastic strips. The presence of confinement effect reduces net stress acting at a material point thus increasing compression capacity of concrete. Further, Young’s modulus of fibre reinforced concrete decreases in comparison with conventional concrete. This is due to softening effect of plastic strips in axial direction. However, progressive increment in loading causes substantial degradation in young’s modulus of conventional concrete whereas for fibre reinforced concrete it remains largely stable. Similar stability in also response is reported for poisons ratio. The present study thus establishes role of plastic strips in developing confinement effect contributing to improved performance and predictability in response of strength and material parameters namely Young’s modulus and poisons ratio.