Aspects of replacing gypsum with other calcium salts in Portland cement

Calcium sulfate (e.g. gypsum) is the common set regulator in Portland cement. It has been shown that ground clinker can be set regulated by calcium salts other than gypsum, in particular calcium acetate, formate and nitrate. Rheology of the paste is improved when gypsum is replaced by other salts, probably due to less water binding and surface hydration products without the needle-like morphology of ettringite. In particular, for calcium nitrate, the cumulative hydration temperature is reduced, which allows for low-energy cement without changing clinker chemistry. Removing calcium sulfate all together may also allow heat curing or evolution of hydration heat in massive structures to exceed 70°C without risking delayed ettringite formation. These aspects have been elucidated by the experiments reported in this paper.