FURTHER-STUDIES OF THE EFFECT OF TEMPERATURE UPON THE SETTING BEHAVIOR OF REFRACTORY CALCIUM ALUMINATE CEMENTS

The embedded thermocouple method has been used to determine a setting time parameter for synthetic samples of pure calcium monoaluminate (CA) and a mixture of CA, CA2 and alpha-Al2O3. The setting time parameter of these samples increases with increasing temperature, reaching a maximum value at ca. 28°C, in a similar manner to the behaviour previously reported for four out of five commercial high alumina cements. This anomalous retardation in setting is therefore confirmed as the normal behaviour of calcium aluminate cements. Any exceptions are probably due to the incorporation of an admixture. An approach based on a kinetic treatment of the data is described. It allows the temperature associated with the maximum setting time parameter to be determined more precisely. From further experiments involving a change in temperature during the dormant period, it is suggested that the most important stage in determining the setting behaviour is towards the end of this period. © 1990.