Effects of pulverized fuel ash on alkali-silica reaction in concrete

Abstract

The partial replacement of Portland cement 〈 pc〉 by pulverized fuel ash 〈 pfa〉 in a series of potentially reactive concretes significantly reduced expansion due to alkali-silica reaction 〈 asr〉 in high alkali mixes, whereas, in marginally reactive concretes with lower alkali levels, 25% addition of a high alkali pfa slightly increased the expansion compared with that developed by the equivalent pc mix. This extra expansion, however, was insignificant in terms of the likelihood of causing physical damage. Pore solution analysis indicated a continuing slow release of potassium ions from the pfa but the observed relationships between asr expansion and pore solution composition of the various concretes studied were somewhat unclear. Petrographic analysis suggested that although no significant expansion-induced microcracking was observed in the cement matrix of pfa concretes, the degree of internal microcracking and gel formation in the reactive aggregate particles was very similar to that seen in the equivalent mixes containing no pfa. This suggests that physical changes to the cement matrix as well as variations in the pore solution alkalinity affect the degree of asr expansion developed by concretes containing pfa.