A Modified Chemical Index to Predict Fly Ash Dosage for Mitigating Alkali-Silica Reaction

Abstract

Abstract It is well chronicled that coal fly ash can mitigate the risk of alkali-silica reaction (ASR) in concrete structures. However, the efficacy of individual fly ashes is highly dependent on their chemical composition. Prescriptive requirements for ASR mitigation have largely focused on whether the fly ash is classified as Class F or Class C per ASTM C618, Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete, whereas performance requirements may require extensive testing to satisfactorily demonstrate mitigation potential of a fly ash. Previous research established the need for an accurate model to predict required fly ash replacement rates for ASR mitigation based on the chemical constituents of cement and fly ash. Therefore, a new model is proposed to account for the availability of each chemical constituent from cement and fly ash separately, utilizing ASTM C1260, Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method), and ASTM C1567, Standard Test Method for Determining the Potential Alkali-Silica Reactivity of Combinations of Cementitious Materials and Aggregate (Accelerated Mortar Bar Method), test data. The successful development of models based on 14-day and 28-day expansion data from these tests is presented in this article.