Influence of cement replacement by limestone calcined clay pozzolan on the engineering properties of mortar and concrete

This study investigates the effect of a new type of blended pozzolan on the hydration, mechanical and durability performance of cement. A blend of limestone calcined clay pozzolan (LCCP) was produced by grinding calcined clay and limestone in a ratio of 2:1 with 2% gypsum. Blends with cement replacement level of 0, 10, 15, 20, 30 and 50% using LCCP were cast. The effect of LCCP on the hydration of cement was investigated using isothermal calorimetry and X-ray diffraction. Mortar and concrete samples were cast to study the influence of LCCP on mechanical and transport properties. The addition of LCCP was found to have a beneficial effect on the early age hydration of cement. The induction period and initial setting time of cement paste were found to reduce on increased cement replacement level. Higher or similar compressive strength was observed for all the LCCP blends as compared to ordinary Portland cement. The pozzolanic reaction of calcined clay and formation of carboaluminates on the reaction of calcium carbonate with alumina helps to develop a refined pore structure that aids in reducing transport properties of concrete such as porosity, rate of water absorption and permeability.