What is ASR (alkali-silica reactivity)?
ASR is an expansive reaction between reactive forms of silica in aggregates, potassium and sodium alkalis, mostly from cement but also from pozzolans, admixtures and mixing water. Other sources of alkali from soil, industrial processes and deicers can also contribute to reactivity. An alkali-silica gel is formed by the reaction and as it draws water from the surrounding cement paste, swells and induces pressure, expansion and cracking of the aggregate and surrounding paste. As a result, map-pattern type cracks, referred to as, alligator patter cracking appears. There are steps to avoid ASR; select proper aggregate; use of blended cements; use of proper pozzolanic materials and contaminant free mixing water.
