Resistance to alkali-aggregate reaction (AAR) of alkali-activated cement-based binders

This chapter presents the susceptibility of alkali-activated binders to alkali-aggregate reaction (AAR), an endogenous reaction that usually occurs in Portland cement concretes in the presence of reactive silica, alkalis and water. Given that alkali-activated materials (AAM) involve large amounts of alkalis mainly used as activators, there are many concerns regarding AAR. After a description of the macro- and microscopic manifestations of AAR, and their mechanisms in Portland cement- based materials, a synthesis of the results found in the literature concerning AAR in alkali-activated binders based on slag, fly ash and metakaolin is presented. AAM can present abnormal expansion due to AAR (especially alkali-activated slag) but the general trend indicates that alkali-activated binders are less affected by AAR than Portland cement is.