Can We Relate ASR Expansion to the Pore Solution Composition?

The composition of the pore solution is a main parameter determining the risk for alkali-silica reaction (ASR) in concrete. The relation between the pore solution composition and ASR expansion was established based on literature data, where concrete or mortar expansion as well as pore solution composition were reported. The general trend was that expansion only occurred at (Na + K) concentration > 300 to 400 mmol/L in the pore solution, or at a hydroxide concentration > 250 mmol/L. The pH of the pore solution alone is not suitable to assess the expansion risk as the pH values strongly depend on the temperature, are demanding to measure and are determined using diverse methods, which are often poorly described. Our literature search showed also that the Al concentration is not a selective criterion for ASR expansion as most pore solutions had Al concentrations below 1 mmol/L and as both the presence and absence of expansion was observed at low Al concentrations. All expanding systems showed also a strong undersaturation of < 10–4 with respect to quartz, which complies with a fast dissolution of silica and thus a high potential for ASR. This study showed that the sum of (Na + K) concentration is a reliable and relatively easily accessible parameter to indicate the potential for ASR in concrete. The study was conducted within the framework of working group 2 of RILEM TC 301 ASR.