Hydration of calcium sulphate hemihydrate in the presence of calcium hydroxide

Abstract A study has been made of the effects of calcium hydroxide on the hydration of calcium sulphate hemihydrate in accelerated, inhibited and unmodified systems, using techniques developed in this laboratory. The results were interpreted in terms of an equation developed earlier, and the parameters k (which is related to the transport of matter in the system) and α0 (which is a measure of heterogeneous nucleation) determined. A small addition of calcium hydroxide leads in all cases to a sharp increase in k. Further additions lead only to effects caused by dilution of the system. Calcium hydroxide has complex effects on α0. These are large in inhibited systems. The basic effects of calcium hydroxide are to increase the concentration of hydroxyl ions which have specific effects, increase the concentration of Ca2+ ions, adsorb inhibitors and extend the system as an inert diluent.