Alkali Silica Reaction (ASR) as a root cause of distress in a concrete made from Alkali Carbonate Reaction (ACR) potentially susceptible aggregates

The mechanism of Alkali Carbonate Reaction (ACR) in concrete made from fine-grained, argillaceous dolomitic limestone coarse aggregates remains controversial. ACR distress is described as an increase in volume caused by the crystallization of brucite during the dedolomitization process. However, recent studies by Katayama suggest that ACR is a combination of the “deleteriously expansive Alkali Silica Reaction (ASR) of cryptocrystalline quartz in the matrix of the reactive aggregates and a harmless dedolomitization that produces brucite and a carbonate halo.” We investigated ACR susceptible concrete extracted from a wharf structure in Quebec, Canada, and determined that ASR was the cause of damage. Optical and SEM-EDS analyses identified ASR gel extending from reactive aggregates to the paste, and X-ray elemental mapping confirmed the gel composition. Silica (Si) was found in the matrix of the aggregate and is the source of reactive silica. These results support ASR as the mechanism in ACR susceptible concrete.