Texas Department of Transportation Fly Ash Database and the Development of Chemical Composition–Based Fly Ash Alkali-Silica Reaction Durability Index

Chemical compositions of approximately 5,500 fly ash samples from 36 power plants inside and outside Texas, compiled by the Texas Department of Transportation (TxDOT) over 18 years, were statistically analyzed in this study. The variations of oxide contents and their correlations were calculated and compared. Oxide contents of Class F fly ashes were found to be more variable than Class C fly ashes. In general, CaO and MgO contents were higher in Class C fly ashes than in Class F fly ashes, whereas the latter had higher ${\mathrm{SiO}}_2$ content. Other oxide contents of the two classes of fly ashes were comparable. Then, to demonstrate the potential beneficial use of chemical composition information of fly ash, an alkali-silica reaction (ASR) durability index was proposed to predict the comparative performance of fly ash in mitigating ASR in concrete. The index value was calculated using ${\mathrm{SiO}}_2$, ${\mathrm{Fe}}_2{\mathrm{O}}_3$, ${\mathrm{Al}}_2{\mathrm{O}}_3$, CaO, and equivalent alkali contents. Previously published research on the use of fly ash in mitigating ASR, using standardized tests, was utilized to validate the proposed index. The index was found capable of differentiating fly ashes in the same class. To verify the usefulness of the ASR durability index, tests were carried out in this study using an ASR reactive sand, two portland cements, four Class C fly ashes, and one Class F fly ash. The results were quite promising, and the use of the fly ash ASR durability index is proposed to screen fly ash for laboratory testing and construction.