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This paper presents the alkali-silica reactivity of andesite and expansion behavior of mortar in NaCl saturated solution. Glassy andesite without silica minerals was non-expansive in a NaCl saturated ...solution, whereas mortar bars using cristobalite-bearing aggregate showed large expansions. Dissolution of glass and cristobalite depend on OH- concentration of alkali solution. OH- concentration of pore solution of mortar under NaCl saturated solution was low. Under this condition dissolved amount of glass is not enough to cause expansion whereas cristobalite dissolved enough. These results indicate one possibility of limited risk of glassy andesite without reactive silica minerals in specific conditions even if alkalis are supplied from environments, such as deicing salts or sea salt as long as the initial alkali content in concrete is controlled under certain amount. In NaCl saturated solution, expansion of mortar bars incorporating cristobalite-bearing aggregate was larger although OH- concentration of its pore solution was lower. This result may be caused by the increment in dissolution of cristobalite because of high ionic strength.show more
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