Decoupling the effects of chemical composition and fineness of fly ash in mitigating alkali-silica reaction

A comprehensive investigation was conducted to determine the individual effects of the chemical composition and particle size of fly ash on alkali-silica reaction (ASR). Test results indicated that the combined oxides content of fly ash showed a better correlation with the ASR expansions than its individual oxides. Mixtures containing finer fly ash fractions registered lower expansions than those containing the corresponding virgin fly ashes or its coarser fractions. Within the usual range of average particle size of 10 to 30 microns, of fly ash, the chemical composition had a more dominant influence on ASR mitigation than the particle size. However, when the average particle size of fly ash decreases below 10 microns, the fineness of fly ash becomes significant in mitigating ASR. In addition, the fineness of fly ash had a more significant influence in mitigating ASR in mixtures containing high-lime fly ashes than those containing low-lime fly ashes. Hence, reducing the particle size of fly ash to finer fractions is an effective strategy to mitigate ASR. The decoupling of the chemical composition of fly ash from its particle size indicated that ASR mitigation can be achieved with any fly ash having a D50 below 5 μm. However, low-lime fly ashes were effective in mitigating ASR even without reducing their particle size