Structure of supercritically dried calcium silicate hydrates (C–S–H) and structural changes induced by weathering

Abstract

The nanostructure of supercritically dried calcium silicate hydrates was researched. This particular drying procedure was used to avoid nanostructure modifications due to conventional drying processes. Thus, in this study, the as-precipitated cementitious C–S–H structure was obtained for the first time. A specific surface area 20 % larger than conventionally dried C–S–H was measured. Given the importance of this nanostructured phase for the properties of hydrated cements, especially when in contact with CO2-rich environments, the supercritically dried C–S–H was weathered for 2 weeks. The structural effects of this weathering process on the C–S–H were researched and calcium carbonate microcrystal precipitation or the presence of silica by-product are reported. Calcite and aragonite polymorphs were observed, as well as nanoporous silica forming globular arrangements. In addition, 2 weeks of weathering was not enough to carbonate the entire C–S–H sample.