Alkali-Silica Reaction (ASR)

Alkali-silica reaction (ASR) is a chemical reaction between reactive silica minerals in some aggregates and alkali hydroxides in cement paste. The reaction forms a gel that absorbs water and expands, slowly cracking concrete from the inside out — often visible as map cracking that develops over years or decades.

ASR is managed by testing aggregate reactivity before use and, where needed, using low-alkali cement or supplementary cementitious materials like fly ash or slag to suppress the reaction.