Fundamental Study of Alkali-Aggregate Reaction

Abstract

This study aims at revealing the effects of the particle size and content of reactive aggregates on the expansion of mortar bars. The reactive aggregates used were opaline amorphous silica from Kagoshima in Japan and powder of pyrex glass (borosilicate glass). They were mixed with the non-reactive aggregate of Toyoura standard sand and a normal portland cement with the equivalent percent Na₂O of 0.71 percent to make a series of mortar. The amount of the reactive aggregate was fixed to 10 percent of the total aggregate by weight for the mortar bars for testing the effect of particle size on the expansion, and it was varied from 5, 10, 20, 50, 70, to 100 percent for the mortar bars for examining the effect of reactive aggregate content on the expansion. The results obtained for the opaline silica are summarized as follows:
(1) The mortar bars with the opaline aggregate show the maximum expansion at the particles size of 0.149-0.238mm and 10 percent replacement.
(2) The surface of the mortar specimens using the fine aggregate is uniformly covered by white fine powder. Some transparent exudation appears on the surface when the coarse reactive aggregates are used.
(3) A scanning electron microscopic study shows that fibrous crystals are newly produced on the alkaline silica gel which covers the opaline aggregate during the storage of specimens. This fibrous crystals may be considered as a secondary reaction product.