Effect of different forms of calcium sulfate on the properties of cement

In our conditions, mainly flue gas desulfurization gypsum (FGD gypsum) is used as a cement setting regulator. When cement is ground, it decomposes into hemihydrate or even anhydrite as the temperature rises. The ground cement is placed in a storage silo where the increased temperature is compounded by increased pressure and the cement properties are affected by the moisture released and by the change in the phase composition of the setting regulator. Under laboratory conditions, hemihydrate and anhydrite II and III were prepared from one type of FGD gypsum. Their purity was monitored by X-ray diffraction analysis and differential thermal analysis. The prepared calcium sulfates were used in different proportions as setting regulators in the laboratory preparation of Portland cements. Technological properties such as strength and solidification were then determined for cements. The hydration process was monitored by the calorimetric method.