Combination of Alkali Threshold of Aggregates and Alkali Loading of Concrete as Predictive Tool of Alkali–Silica Reactivity in the Field

Abstract

A new protocol to predict the likelihood that concrete develops alkali–silica reaction in the field is presented. This protocol, based on the relationship between the alkali threshold of the aggregate combination and the alkali loading of the concrete, aligned with the long-term expansion data of 31 concrete blocks from three different exposure sites. Additionally, the alkali threshold of the aggregate combination used in the concrete blocks was found to display a significant sensitivity toward the mineralogy of the nonreactive fine aggregates used in conjunction with the reactive coarse aggregates and portlandite content of the binder. The results of this study emphasize the importance of addressing the existing knowledge gaps in the interactions between coarse and fine aggregates with respect the alkali threshold of the system. Further, the study underscores the fact that the combined alkali threshold of coarse and fine aggregates provides valuable insight regarding the long-term field performance of a concrete mix. The alkali threshold of the aggregate combination used in concrete, defined as the minimum alkali content needed to trigger the alkali–silica reaction (ASR) in the system, is a good indicator of potential alkali-reactivity in the field. This study introduces a new and simple ASR risk assessment chart, in which the alkali threshold of the aggregate combination and the alkali loading of the concrete are combined to provide valuable insights regarding the long-term field performance of a concrete mix. The outcomes of the ASR risk assessment chart aligned with the long-term expansion data of 31 concrete blocks from three different exposure sites.