Hydration of calcined bentonite Portland blended cement pastes

Abstract

The formation of free lime (CH) during the hydration of Ordinary Portland Cement (OPC) decreases the durability of cement structures. The pozzolanic properties of calcined clays allow to avoid this drawback. So, the reaction kinetics of the OPC/calcined bentonite blended cement pastes were investigated. The results show that the water of consistency as well as setting time increase gradually with the addition of calcined bentonite at the expense of OPC. The combined water content also increases with the substitution of OPC by calcined bentonite up to 9-12 mass% and then decreases. The free lime content increases up to 3-7 days and then decreases. Also, the bulk density increases slightly, while the apparent porosity decreases. The compressive strength increases sharply up to 28 days, and slightly increases up to 90 days due to the pozzolanic reactions of calcined bentonite. The cement pastes containing 12 or 15 mass% bentonite were adversely affected at all curing ages of hydration. The SEM micrographs indicate that the hydration products of the OPC/calcined bentonite cement pastes are the same as those of the pure OPC pastes, but with different ratios, crystals and morphologies.