Studies on thermal dehydration of the hydrated Ca7ZrAl6O18 at different water-solid ratios cured at 60 °C

In this paper, the results of experimental study concerning the hydration behavior of Ca7ZrAl6O18 with water to solid (w/s) ratios of 0.5 and 1.0 at 60 °C are presented. Hydration products were studied by XRD, DTA-TG and SEM/EDS after 24 h; 3, 7, 14 and 21 days of curing and hydration. Ca7ZrAl6O18 in paste form, at w/s ratio of 0.5, showed one clearly visible endothermic effect at about 310 °C due to the dehydration of crystalline C3AH6. In the paste at w/s ratio of 1.0, the thermal decomposition of C3AH6 occurred at about 317 °C, and was preceded by an endothermic effect with a minimum at 277 °C corresponding to the crystalline Al(OH)3 decomposition. The results showed that the hydration of Ca7ZrAl6O18 phase was especially a time dependent effect in regard to the separation of CaZrO3. SEM observations have shown typical morphological changes for each hydration period and water/solid ratios.