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

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.

Cement/clay interactions – A review: Experiments, natural analogues, and modeling

“…Dissolution of the quartz by the cement waters enables the precipitation of CSH minerals such as tobermorite, hillebrandite, foshagite (Bérubé et al, 1990;Savage et al, 1992;Bateman et al, 1999), while dissolution of the Al-bearing micas and feldspars enables precipitation of CASH-phases as hydrogrossular in addition to CSH (Bérubé et al, 1990;Savage et al, 1992;Bateman et al, 1999;Hodgkinson and Hughes;. The Ca will thus be trapped by three phase types, i.e.…”

Nature of C-(A)-S-H Phases Formed in the Reaction Bentonite/Portlandite

“…In addition to laboratory experiments, zeolites, C-S-H, and C-A-S-H phases have also been observed in natural and archaeological analogues [21,22]. Consequently, geochemical models of cement/bentonite interaction usually try to predict the long-term stability of a wide range of possible C-S-H and C-A-S-H phases of varying composition, which in most cases are based on thermodynamic data derived from theoretical calculations [23].…”

Impact of an Alkaline Solution on the Chemistry, Mineralogy, and Sorption Properties of a Typic Rhodudult Soil

“…These analyses were performed to give an indication of the formation of the CSH phases, since these phases are often too finely grained and mixed with other phases to have their composition precisely determined by conventional XRD or EDX (Bérubé et al, 1990;Savage et al, 1992;Bateman et al, 1999;Hodgkinson and Hughes, 1999). The EDX analyses, which were made on each one of the surfaces indicated, are presented in figures 3c to 3h.…”

“…These studies demonstrated that the nature and extension of the modifications caused by the interactions of the minerals with the alkaline solution depend on the chemical/mineralogical composition of the initial solid material, the composition of the alkaline solution, and the alteration conditions, including temperature, period of exposure, and size of the solid sample (Gaucher and Blanc, 2006). Several studies show that the dominant interaction mechanism of minerals with alkaline solutions is the dissolution of primary aluminosilicates followed by precipitation of secondary phases of hydrated calcium silicates (CSH) (Bérubé et al, 1990;Savage et al, 1992;Hodgkinson and Hughes, 1999;Wieland and Loon, 2003). These CSH phases are formed by a combination of Al and Si dissolved from the sample and Ca from the alkaline solution.…”