Identification of Dehydrated Gypsum in Portland Cement
J. L. Gilliland
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False set in portland cement is usally attributed to dehydrated gypsum. Inasmuch as hemihydrate is much more soluble than gypsum, the concentration of sulfate ion in the liquid phase of cement pastes can be used to identify cements in which dehydrated gypsum is likely to cause trouble. The solublity test correlates with the penetration test used to detect stiffening. While X-ray diffraction and differential thermal methods can be used to identify various forms of calcium sulfate in high concentrations, they are not applicable to the study of calcium sulfate in portland cement.