ON THE CAUSE OF THE ANOMALOUS SETTING BEHAVIOR WITH RESPECT TO TEMPERATURE OF CALCIUM ALUMINATE CEMENTS

As the temperature of hydration of monocalcium aluminate is increased, the setting time becomes longer until it reaches a maximum value at 28°C. Above this temperature, the setting time decreases rapidly with increasing temperature. Various explanations for this phenomenon are critically reviewed and most are shown to be unable to explain all the observations that have been reported. It is proposed that the anomalous setting behaviour is because none of the hydrated calcium aluminates can form readily in the range 25-30°C. The nucleation of CAH10 is no longer favoured on thermodynamic grounds, whilst the rate of formation of C2AH8 is very sluggish, and C3AH6 can only be formed via conversion of these metastable hydrates in this temperature range. Hence precipitation of the hydrate crystals to produce a set cement takes longer than at other temperatures. © 1990.