Effect of capping materials on the compressive strength and modulus of elasticity of concrete

Capping is a technique to ensure smooth and level surface at the both ends of the concrete specimens that are subjected to the axial load during compressive strength testing. ASTM C1552 specifies bonded caps, particularly gypsum plaster or molten sulfur, as appropriate capping materials to determine the compressive strength of concrete cylinders. However, the bonded caps have several limitations like as such as longer preparation time, expensive, intensive and skilled labor in addition to potential to health hazard. Hence, it is essential to explore alternative capping materials in concrete cylinders which are economical, reusable, as well as potential to reduce health vulnerability to determine the compressive strength of concrete. This research investigates the feasibility of a number of un-bonded capping systems such as soft rubber, neoprene, geotextile and fiber board as an acceptable technique to determine the compressive strength and modulus of elasticity of concrete specimens subjected to axial load. In this research, gypsum plaster capping is chosen as the control method and compared with others un-bonded capping materials. It has been observed that concrete specimens containing neoprene capping system provide good agreement as a reliable alternative of gypsum capping system followed by soft rubber, geotextile and fiber board capping systems.