Effect of Temperature on the Structure of Set Gypsum Plaster

Abstract

VARIATIONS within the normal range of temperature do not exert a very profound effect upon the rate of hydration of gypsum plaster^1,2. For example, Fig. 1 shows the maximum rate of increase of temperature and the induction period (defined as the time required for the rate of increase of temperature to reach 0.1° C. per min.) plotted against initial temperature for a commercial plaster consisting predominantly of the so-called hemi-hydrate of calcium sulphate. The plaster had been allowed to age until it gave steady results. The reactions were carried out in a Dewar flask so that the increase in temperature is a valid parameter of the reaction. It is seen that the induction period is constant from 0° to 40° C., above which temperature it increases gradually. The maximum rate reaches a feeble maximum at about 25° C. It appears, however, that at higher temperatures the rate of hydration does drop considerably³. Results similar to those shown in Fig. 1 were obtained for another plaster from a different source.