The addition of caesium to concrete with alkali-silica reaction: Implications on product identification and recognition of the reaction sequence

The formation of alkali-silica-reaction (ASR) products in concrete aggregates generates stress leading to the formation of cracks proceeding from the aggregates into the cement paste. However, there is little knowledge on the initial ASR products formed in aggregates before the cracking occurs, as their small volume considerably complicates analysis. In this study, a new approach for identification and visualisation of ASR product formation leading to concrete damage is presented. Caesium is added as a tracer during concrete production. Because it is mainly incorporated in ASR products, their backscattering contrast in the scanning electron microscope is considerably increased. This makes it possible for the first time to follow the temporal and spatial progression of ASR with resolution in the nanometre scale, thereby delivering a coherent reaction sequence.