Investigation on the Effect of Calcined-gypsum on the Early Hydration of Portland Cement

By experiment methods of DTA,XRD,IR,Chemical combined water analysis,Ca(OH)2 content and so forth,the effect of gypsum and calcined-gpysum on the early hydration of Portland Cement was investigated. The result showed that the hydrat product of the cement added calcined-gypsum has more Ca(OH)2 content during whole hydrating stage,less chemical combined water before 1 day and more after 1 day,and ettingite can not formed before 1 day comparaed with adding gypsum, .The reserch indicated that adding calcined-gypsum instead gypsum to cement can reinforce the early strength of cement, because the aluminate phase present in clinker can not hydrat to form ettringite during 1 day due to low dissolution rate of calcined-gypsum, so retarding action of ettingite on clinker hydration is decresed, the whole clinker mineral hydration is accelerated, the paste strength is incresed.