Effects of packing density and water film thickness on fresh and hardened properties of ternary cement pastes

Optimisation of the packing density of cementitious materials by the addition of supplementary cementitious materials (SCMs) is a way of obtaining the same service properties with less embodied energy and reduced carbon dioxide emissions. In this paper, ternary cement pastes containing metakaolin (MK) and limestone filler (LF) finer than ordinary Portland cement (OPC) were studied to evaluate the effects of these SCMs on packing density and water film thickness (WFT). The flowability of the pastes at different water to cementitious material ratios by volume ((w/cm)_v = 0·5 to 1·0) was evaluated by mini-slump and Marsh cone tests to evaluate the opposite effects caused by the incorporation of finer particles (increase of free water to lubricate the particles due to higher packing and increase of specific surface area). The incorporation of LF and MK increased the flowability when (w/cm)_v was increased over the optimum water demand corresponding to the maximum packing density. The rheological properties of the pastes were primarily dominated by the relative solid packing fraction and the flowability was found to be mainly governed by the WFT. The incorporation of finer particles accelerated the setting time. The reactive particles (OPC and MK) can be replaced by LF up to 20% to obtain a similar compressive strength, as validated by Powers’ model.