New Considerations in Predicting Mitigation of Alkali-Silica Reaction Based on Fly Ash Chemistry

The purpose of this study was to determine the ability of high CaO and/or high-alkali (${\mathrm{Na}}_2{\mathrm{O}}_{\mathrm{eq}}$) fly ashes to control alkali-silica reaction (ASR) in mortar bars. The research focused on using an industry standard test method to validate if the chemical index characterization technique common in the literature could be used to accurately predict the replacement levels of investigated fly ashes to mitigate ASR. Results confirmed that low and moderate CaO content fly ashes (with both low and high ${\mathrm{Na}}_2{\mathrm{O}}_{\mathrm{eq}}$ contents) were more effective in mitigating ASR compared to higher CaO and higher ${\mathrm{Na}}_2{\mathrm{O}}_{\mathrm{eq}}$ ashes. A chemical index characterization technique was applied to calculate the required fly ash replacement based on the raw fly ash chemistries and 14-day industry standard results without fly ash (e.g., control). The index was shown to work well for low-CaO and low-alkali ashes; however, adjustments are necessary to use this methodology to predict replacement levels of moderate and high-alkali fly ashes. The industry standard test was shown to be the best method to date to determine the efficacy of high-CaO and/or high-alkali fly ashes. The data presented will also aid in the understanding of how alkali contribution from fly ashes should be considered in the development of new rapid test methods.