Assessment of the potential alkali-reactivity of aggregates for concrete by image analysis petrography

The petrographic method RILEM AAR-1 has proven to be very effective, reliable and time efficient in assessing the potential alkali-reactivity of aggregates for concrete when performed by experienced petrographers. However, on a global scale, some challenges in the assessment of so-called “slowly” reactive aggregates have been reported. This paper uses image analysis petrography to assess quantitatively the microstructure of aggregates for concrete. Grain size and grain shape descriptors were calculated for 11 aggregate samples from 3 countries (Italy, Norway and Portugal), including reactive and non-reactive rock types. Results from image analysis petrography were critically reviewed against expansion data and reported experience in structures. It was concluded that image analysis petrography can be used as a supplementary technique to overcome some of the limitations of the traditional petrographic method RILEM AAR-1 reported in the literature and improve its value as a tool to evaluate the potential reactivity of aggregates for concrete.