Determination of calcium sulfate hydrates in building materials using thermal analysis

Calcium sulfate exists as both a dihydrate and a hemihydrate. Chemical or X-ray diffraction techniques have been used to detect the presence of these two hydrates. However, neither of these techniques is able to provide quantitative information at the levels of interest in building materials. Two thermal analyses provide viable techniques: differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). DSC measures the heat associated with reactions in materials and follows the conversion of dihydrate to the hemihydrate and then the anhydrate. TGA, which measures weight changes in materials during reaction, follows the conversions based on the stoichiometric weight quantitation.