Effect of silica fume and rice husk ash on alkali-silica reaction

The alkali-silica reaction (ASR) that occurs between the alkaline hydroxide s in cement paste and reactive minerals in the aggregate produces an expans ive gel that may cause cracking and displacement in concrete structures. Cu rrently, pozzolanic materials are used to prevent or minimize this cracking . An experimental program was undertaken to study the effect of different l evels of cement replacement by silica fume (SF) or rice husk ash (RHA) on t he expansion of mortar bars containing two types of reactive aggregates. Th e morphology and composition of the ASR gel were determined using scanning electron microscopy (SEM) and energy-dispersive x-ray (EDX). The results in dicate that it is possible to significantly reduce the mortar-bar expansion for both types of aggregate using either SF or RHA. As predicted by double -layer models, the expansion of the mortar bars was highly correlated to th e gel composition. The experimental results were also analyzed using the Kr uskal-Wallis nonparametric method to validate the effect of these pozzolani c replacements on ASR gel composition.