Evaluating the Use of Alkali-Silica Reaction Mitigation as a Metric for Assessing Pozzolanicity

Abstract

Abstract Regional shortages in fly ash have led to the consideration of alternative pozzolanic sources, including ponded coal combustion products (CCP). Additionally, prevention of alkali-silica reaction (ASR) expansion remains an important consideration in construction, but with less fly ash available, alternate means for mitigation are sought. Here, the efficacy of ponded CCP in limiting ASR expansion is evaluated, considering 13 ponded CCP samples obtained from 4 power plants. Each was evaluated in accordance with ASTM C618-19, Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete, to assess specification compliance and to determine its ability to evaluate the pozzolanic reactivity of tested supplementary cementitious materials (SCMs). Additional testing was performed on ASR mitigation to determine if pozzolanicity among candidate SCMs can be assessed through comparisons to inert quartz. Blended mortars were tested at 20 % replacement by weight for compressive strength via 2-in. mortar cubes, whereas ASR mitigation was tested through the accelerated mortar bar test (ASTM C1567-21, Standard Test Method for Determining the Potential Alkali-Silica Reactivity of Combinations of Cementitious Materials and Aggregate (Accelerated Mortar-Bar Method)). It was determined that the ability to meet strength activity index limits is heavily influenced by the physical state of the ash (primarily loss on ignition) instead of its chemical reactivity. Additionally, many materials that meet ASTM C618 specifications poorly mitigate ASR damage because of a lack of pozzolanicity, which was related to higher Fe2O3 contents. Based on these results, the following changes to ASTM C618 are recommended: (1) ASTM C1260-21, Standard Test Method for Potential Alkali Reactivity of Aggregates (Mortar-Bar Method),/C1567 14-day expansion for a control mixture and a 20 % SCM mixture when blended with a reactive aggregate reported relative to the control; (2) remove Fe2O3 from the primary oxide content calculation; and (3) include an upper limit of 12 % on Fe2O3 content. These changes will improve ASTM C618’s ability to reliably report a candidate SCM’s reactivity and potential to mitigate ASR.