Hydration of hydraulic materials – a discussion on heat liberation and strength development

The materials for low heat cement are discussed from the point of view of the relationship between the strength development and the heat of hydration. The strength development due to the hydration of hydraulic materials is understood to be due to the filling by hydrates of the space that was initially occupied by water. The strength of porous materials can be well expressed by the empirical Ryshkevitch's law. When considering the materials to be used for low-heat cement the rates of heat development are the usual criteria, but instead the amount of heat developed should be regarded as most important, and particularly the ratio of the amount of heat liberated to the volume of solid increased by the hydration. The heat required for fill a unit pore volume was evaluated for some materials, such as C₃S, C₂S, C₃A and granulated blast furnace slag. When C₃S filled a unit volume of space with hydration products such as C–S–H and C₂S did with C–S–H and CH, C₃A did with AFt, C₃A did with AFm18 and slag did with C–S–H and AFt, the amounts of heat liberated were calculated as 225, 136, 266, 326, 177 cal/ml increase in volume, respectively. It was clearly shown that in these materials C₂S had easily the minimum heat liberation. It was also found that the solid volume obtained by hydration was proportional to the amount of mass of water hydrated; that is, water solidifies as a material with density of approximately 1·17 g/cm³. This also means that the amount of chemical shrinkage was proportional to the amount of water required for hydration.