Reliable quantification of AAR damage through assessment of the Damage Rating Index (DRI)

This paper presents the results of the condition assessment of twenty concrete mixtures incorporating ten different reactive aggregates through the Damage Rating Index (DRI), a microscopic and semi-quantitative petrographic tool, with the aim of verifying the development of distress due to alkali-aggregate reaction (AAR) as a function of the specimen's expansion (i.e. from 0.05 to 0.30%). The DRI was found to provide a reliable assessment of the degree of damage in the concretes incorporating reactive fine or coarse aggregates. An envelope of DRI damage assessments against the expansion level of the affected materials is proposed. For all alkali–silica reactive aggregates investigated, the progress in counts and proportions of opened cracks in the aggregate particles and in the cement paste, with and without gel, as well as the crack density parameter, were found to be diagnostic petrographic features for quantifying ASR progress. Moreover, a qualitative ASR distress model in concrete was defined.