Quantitative determination of anhydrite III from dehydrated gypsum by XRD

Technical OPC contains mixed sulfate carriers in varying amounts. Gypsum and anhydrite are added to the clinker during the milling process where the gypsum dehydrates partially to bassanite and anhydrite. Due to different hydration kinetics of these phases, it is crucial to be able to characterize the composition of sulfate in a cement system to reach an optimal and reproducible cement hydration. In the current paper different calcium sulfate compositions are investigated by XRD methods in order to identify phase content. Special focus is put on the discrimination of the hemihydrate (bassanite) and anhydrite III as well as on transformation processes of anhydrite III through ambient humidity.