Abstract : The paper discusses the physical and chemical effects of the phenomena associated with the formation of hydrated sulfates in concrete, aggregate, paste, and mortar. The relation of the physical properties of the material surrounding the locus at which the hydrated sulfate is produced to the amount of expansion that results, the degree to which the expansion can be reduced by restraint, the force required to prevent expansion or to prevent the reaction from taking place, the consequences of the restraining force being uniaxial, biaxial, or triaxial rather than hydrostatic are considered. (Author)