Alkali-reactive minerals and reaction products in some andesites.

Abstract

Alkari-silica reactions have a harmful effect on some andesites. In the present paper, the alkali -silica reactions in andesitic rocks were examined by means of optical and X-ray diffraction analyses and the standard test with mortar bars (ASTM C227). Furthermore, by the microscopic examination of the dyed thin section made from a mortar bar, various types of reaction products including cracks and spherules were identified and distinguished. The contents of alkari-reactive minerals such as cristobalite, tridymite, and glass, which are present in andesites, are irregular and change very much with the location. The results of the test on mortar bars had no direct correlation with any kind of alkali -reactive minerals . It is difficult to determine the role of these alkali-reactive minerals in the expansive alkali-silica reaction, because there are many factors in the reaction.