Alkali- Aggregate Reaction
Certain aggregates contain reactive varieties of silica, which may be susceptible to attack by alkalies originating from cement or other sources. For alkali- aggregate reaction (AAR) to occur following attributes should be present: sufficient alkalies in concrete:; a critical amount of reactive silica in the aggregate; and sufficient moisture. Relative humidity has an important influence on AAR, and high temperature with adequate moisture generally accelerates ASR (alkali- silicate reaction), whereas low temperature slows it down. In clause no. 18.104.22.168 , IS: 456-2000 gives the precautions need to be taken out to avoid AAR.