The realistic assessment of ASR in concrete and the identification of suitable measures to prevent it continue to pose major challenges to the concrete and aggregate industry. The recent AASHTO R 80 Practice and the ASTM C 1778 Guide appear to have significantly improved the assessment of aggregates for potential ASR and the selection of appropriate mitigation measures to allow the use of potentially reactive aggregates in concrete construction. However, concern has been raised that, since these tests are based on concrete mixtures with rather high cement and alkali contents, they may not properly represent the more realistic mixtures with moderate or low cement and/or alkali contents generally used in concrete construction and may also result in the rejection of aggregates that otherwise might have performed well in field concrete. Furthermore, some recent data indicates that the amount of supplementary cementitious materials (SCMs) recommended by these tests may not adequately control expansion in outdoor exposure blocks with high contents of high-alkali cements.

 Under Project 10-103, “Improving Guidance of AASHTO R 80/ASTM C 1778 for Alkali-Silica Reactivity (ASR) Potential and Mitigation,” the University of Texas at Austin was tasked to address the present shortcomings of AASHTO R 80/ASTM C 1778. The study involved a critical literature analysis with regard to the issues with various ASR tests and the gaps and disconnects in the current state of evaluation of field concrete mixtures for ASR potential. Based on this analysis, an extensive test matrix was developed and implemented with particular attention to concrete blocks with lower cement content and and/or alkali loadings. It will take some time before those low-alkali blocks show any noticeable ASR-related changes because of rather low occurrence of ASR in those blocks. The project team was still able to use historic database of laboratory and exposure site data to recommend improvements to AASHTO R 80/ASTM C1778.

The recommendations proposed in this report will be updated in future when the long-term expansion data from the exposure blocks cast in this project becomes available for use. This data is being stored in an online database.

NCHRP Report 1083 provides recommendations for the improvement of the guidance of the AASHTO R 80/ASTM C1778 test methods for preventing alkali-silica reactivity (ASR) in concrete. Also proposed are guidelines for some promising new or recently developed test methods for assessing aggregate reactivity and taking preventive measures. Further improvements to AASHTO R 80/ASTM C1778 will be possible when long-term monitoring data for outdoor exposure concrete blocks cast in this project becomes available.