Effect of Blended Fly Ashes in Mitigating Alkali–Silica Reaction

The role of chemical composition of fly ash in mitigating alkali–silica reaction (ASR) was examined, and findings were used to evaluate blends of high-lime and low-lime fly ashes in their ability to mitigate ASR. In addition, the influence of particle size (fineness) of fly ashes on ASR mitigation was evaluated, so that the relative significance of fineness and chemical composition of fly ash in mitigating ASR could be established. Findings from these studies confirm results from studies on the influence of lime content of ash on ASR mitigation. Blended fly ashes containing content of no more than 16.5% equivalent calcium oxide and no less than 66% equivalent silicon dioxide were found to be effective in mitigating ASR. The performance of blended fly ashes was comparable with that of virgin fly ashes of equivalent chemical composition. Finer fly ashes showed better ASR mitigation in the case of low- and intermediate-lime fly ashes. However, in the case of high-lime fly ashes, the effect of fineness could not be clearly resolved. Findings from this study indicate that both the physical and the chemical properties of fly ash are important in selecting ashes for developing blends that are effective in ASR mitigation.