Silica dissolution in impure sandstone: application to concrete

Abstract

Dissolution and leaching of silica in concrete aggregate leads to structural deterioration by the hygroscopic and swelling properties of the resulting gel, causing cracking of the concrete. The process is referred to as ASR: alkali–silica reaction. In Dutch concrete with relatively alkali-rich ordinary Portland cement (OPC), chert pebbles are regarded susceptible to ASR owing to their fine-grained microstructural features and poor crystallinity. The damage in the three concrete structures presented in this study, however, is caused by reaction of fine-grained sandstone containing muscovite and interstitial clays. Despite the coarser microstructure and higher crystallinity, sandstone reacts more violently than chert in the same samples. Petrographical observations on reactive sandstone coincide with recent descriptions of catalyzed silica dissolution in diagenetically altered sandstones. Low Na 2O-equivalents decrease even further with increasing degree of cracking. The combination of low bulk alkali content, microscopical characteristics of the reactive sandstone, and its resemblance to catalyzed quartz dissolution in diagenetic sandstones strongly suggests that a similar mechanism of catalyzed dissolution could play a significant role in ASR-induced aggregate deterioration in concrete.