Effects of Soak Solution Type on Alkali Release from Volcanic Aggregates ? Is Alkali Release Really Responsible for Accelerating ASR Expansion? ?

Alkali release from aggregates is considered to cause expansion due to the alkali-silica reaction (ASR), owing to the increase in the hydroxide ion concentration (namely pH) of the pore solution. However, a direct validation of this assertion has not yet been made. In this research, the effects of the type of soak solution, which might better mimic the composition of the pore solution, on the behavior of alkali release from aggregates are investigated through immersion tests of aggregates. More importantly, accompanying ions dissolved from the aggregates are also measured in order to determine the mechanism for the increase in hydroxide ion concentration of the pore solution. The test results show that this increase can barely be observed, despite a considerable amount of alkalis being released. The results critically question the conventional view that alkali released from an aggregate serves to accelerate the ASR.