Alkali-Silica Reaction (ASR) Mitigation in High-Alkali Content Cements

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This study presents a comprehensive evaluation of alkali-silica reaction (ASR) in concrete mixtures, focusing on the performance-based specifications and the critical role of supplementary cementitious materials (SCMs) in mitigation. A modified version of American Association of State Highway and Transportation Officials (AASHTO) T380 was developed to assess ASR susceptibility in job-specific mixtures. A moderately reactive aggregate, i.e., R1 aggregate reactivity class per ASTM C1778, was used, as this is representative of reactive aggregates in Virginia. Concrete prisms were prepared using actual project mix designs, immersed in alkaline host solutions matched to expected pore solution chemistry, and monitored for expansion over 84 days. The results demonstrated that increased cement content—and thus higher alkali loading—consistently led to greater expansion, whereas plain concretes without SCMs remained vulnerable to ASR regardless of cement alkali content or total alkali loading. These findings highlight that prescriptive specification restricting alkali content of cement or total alkali loading, as several state departments of transportation have historically practiced, is not a reliable standalone strategy. Indeed, infrastructure performance revealed that low-alkali cements and alkali loading limits alone do not prevent ASR when reactive aggregates are present. However, for simplicity, prescriptive specifications with appropriate safety factors can be considered. The proposed modified AASHTO T380 method also provides a more realistic framework for determining SCM dosages. By calibrating SCM levels against specific alkali loadings and aggregate reactivity in job mixtures, this approach supports a performance-based framework for ASR mitigation. SCMs such as fly ash, slag, and silica fume were confirmed to be highly effective in mitigating ASR when applied in sufficient dosages. However, their effectiveness is mix-specific, depending on alkali loading, aggregate reactivity, and SCM type. The results also indicate that cements with higher alkali contents can be used safely when appropriate SCM dosages are incorporated, providing greater flexibility and sustainability in mix design.

 

_{Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.}

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