Mechanical and physico-chemical properties of hardened Portland cement pastes containing hydrophobic admixtures - Part 1: Compressive strength and hydration kinetics

Water-repellent materials are used as admixtures for cement mortar and conc rete to reduce the absorption of water under low pressure. The aim of this investigation is therefore to elucidate the effect of such materials on the compressive strength and hydration kinetics of Portland cement pastes. The materials used in this investigation were long chain, fatty acids (such as stearic acid) and vegetable oils. Different ratios of the admixtures were used, namely 0, 0.25 0.45, 0.75 and 1.5 wt.% of the dry cement. The results of the compressive strength were correlated with those of the hydration. k inetics. A slight retardation effect for the hydration of Portland cement w as observed, especially at relatively high doses of the hydrophobic admixtu res. In addition, the phase composition of the hydration products was inves tigated using X-ray analysis.