An ASR exposure site after 30 years – Chemical composition of hydrates and ASR products

Concrete specimens containing two aggregates susceptible to alkali-silica reaction (ASR) and various supplementary cementitious materials (SCMs) have been exposed outdoors since 1992. After 30 years of expansion monitoring, some specimens were cored to conduct an in-depth analysis of their condition. The chemical compositions of the hydrates and the ASR products were quantified with SEM-EDS. All SCMs increased the Si/Ca of the C-(A)-S-H, but the extent varied depending on their composition, amount and degree of reaction. Larger amounts of SCMs resulted in lower degrees of reaction. The ASR products inside aggregate particles of non-boosted concrete mixtures were crystalline. Their Ca/Si was in the range 0.21–0.24, independent of the binder and the aggregate types. The (Na + K)/Ca was usually in the range 0.31–0.35. The Na/K varied more, correlating with the respective ratios in the binder. The Al content of the ASR products inside aggregate particles was not influenced by the presence of Al-rich SCMs.