Alkali-silica reaction (ASR)
A slow chemical reaction between alkalis in cement and reactive silica in certain aggregates, forming a gel that swells with moisture and cracks the concrete from within.
What does alkali-silica reaction (asr) mean?
ASR damage develops over years or decades and produces characteristic map cracking, gel exudation, and expansion that can misalign structures. It requires reactive aggregate, sufficient alkalis, and moisture, so removing any one prevents it. Mitigation strategies include testing aggregates, using pozzolans or slag to bind alkalis, and limiting cement alkali content.
In practice
Regions with reactive aggregate deposits write ASR mitigation into standard specifications, and it is a routine part of mix approval there.