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This paper discloses that a fairly substantial part of the reduction in compressive strength of concrete in which alkali-silica reaction has occurred is not due to the alkali-silica reaction itself, but because of such facts that alkali in cement makes the structure of the hardened cement mass porous, that there is a great difference in the tendencies of compressive strength reduction between cases of using glassy andesite and chert as reactive aggregates, and that the ratio of decline in compressive strentth becomes very low when expansion due to alkali-silica reaction reaches about 0.2%. Furthermore, it is shown that along with non-crystalline part in the constitution of concrete being increased with progress of reaction, there is an increase in homogeneity of structure, backing up the results obtained through experiments.

Dyeing the products of the alkali-aggregate reaction made it possible to distinguish them from the components of the concrete under a microscopy. Cyanoacrylate mixed with a coloring substance was used to dye the alkali-silica gel red.Cyanoacrylate reacts readily with water contained in gel but not with the components of the concrete. Examination of dyed thin sections revealed a few concrete cores with expansion of alkali-silica reactive aggregates. This method appears to be useful for observing the alkali-aggregate reaction.