Impact of chloride-rich environments on cement paste mineralogy

Chloride is widely present in the service environment in which Portland cement concretes are used. High local concentrations of chloride can develop by wicking and evaporation, as for example in splash zones. The parallel sequence of mineralogical changes with increasing chloride forms Friedel's salt and subsequently, compounds containing Ca(OH)2, CaCl2 and H2O in ratios 3:1:12 and 1:1:0. New X-ray and thermal analysis data are presented for these phases. Their phase equilibria are presented and it is shown that Ca(OH)2 coexists with 3:1:12 at least up to 55 °C. It is suggested that the low physical density of 3:1:12, 1.62 g/cm3, and high water content contribute to the potential for expansion attending its formation in hardened matrices.