EFFECTS OF CALCINED GYPSUM ON EARLY HYDRATION OF PORTLAND CEMENT

Effects of gypsum and calcined gypsum on the early hydration of portland cement were investigated by means of DTA, XRD, IR, and chemically combined water and Ca(OH)2 content. Results show that the cement pastes with calcined gypsum had more Ca(OH)2, less chemically combined water and no ettringite in the first day of hydration in comparison with the cement pastes with gypsum. The research indicates that calcined gypsum instead of gypsum accelerated the formation of early hydration products because the aluminate containing phases in clinker can not hydrate to form ettringite during the first day due to the low dissolution rate of calcined gypsum.