The mineralogy and geochemistry of cement/rock reactions: high-resolution studies of experimental and analogue materials

Abstract

Abstract Cements are commonly used to engineer the environment around waste disposal sites. As groundwaters move through these sites, cement gradually dissolves and a reactive ‘hyperalkaline plume’ forms downstream. Published experimental and modelling studies of cement/rock reactions suggest that host-rock mineralogy will dissolve and be replaced initially by high-volume calcium silicate hydrate gels, and later by zeolites. Results of mineral/alkali experiments are presented. Examination of the reaction products, at the high analytical resolution afforded by ATEM, show new disordered phases which are structurally related to calcium silicate hydrates but are highly aluminous (relative to the published results of previous work). A review of archaeological analogue studies shows that old cement pastes easily become carbonated in the presence of CO 2 or carbonate waters. If protected from carbonation, however, cement gels can survive unchanged for thousands of years. New results of an ATEM examination of 1700 year-old Roman mortar from Hadrian’s Wall confirm that cement gels remain poorly ordered and reveal an aluminous CSH gel phase to be the chief product of mortar/dolerite reaction. These findings are discussed in the context of barrier engineering.