Hydration, microstructure and phase composition of composite cements containing nano-clay

Abstract

The effect of partial replacement of ordinary Portland cement (OPC) with nano-clay (NC) on the performance of physico-chemical, mechanical, hydration characteristics and microstructure of composite cement pastes containing ordinary Portland cement (OPC) and ground blast-furnace slag (GBFS) was studied. Initial and final setting times are accelerated by the partial replacement of OPC with NC. The values of compressive strength, bulk density, chemically combined water content and gel/space ratio of composite cement pastes increase by using NC up to 6mass%, then decrease by further replacement up to 8mass%. The free lime contents of composite cement pastes increase from 1day up to 3days, then decrease from 7days up to 90days. NC activates the hydration reaction of OPC and GBFS. SEM micrograph of mix M4S40 (54% OPC+6% NC+40% GBFS+1%SP) deposits the presence of micro- and nano-crystalline CSH gel with dense interlocking close linkage structure composed mainly of larger crystalline hydrates. It can be concluded that 6mass% NC is the optimum replacement level.