The mechanism of alkali-aggregate reaction in concrete/mortar and its mitigation by using geopolymer materials and mineral admixtures: a comprehensive review

Abstract

Concrete is an indispensable material in the construction industry; however, it is susceptible to many damaging mechanisms such as Alkali Aggregate Reaction (AAR). AAR initiates when alkali hydroxide in cement reacts with aggregates (fine/coarse) containing a bulk amount of silica or carbonate thereby triggering an Alkali-Silica Reaction (ASR) or Alkali Carbonate Reaction (ACR) respectively. AAR has very adverse effects on different properties of concrete including durability, stiffness, impermeability, strength, and aesthetics. AAR causes severe expansion and cracking in concrete. Although several methods can be used to mitigate AAR, the most suitable method for controlling AAR and enhancing concrete properties is the incorporation of geopolymer materials and mineral admixtures in concrete. This paper provides a comprehensive review on the mechanism, causes of AAR, and the behavior/performance of different geopolymers (a combination of an alkaline liquid with fly ash, metakaolin, and blast furnace slag) and mineral admixtures (fly ash, highly reactive metakaolin, rice husk ash, waste glass powder, ground granulated blast furnace slag, silica fume, and trass) when used to eliminate AAR and their effect on different mechanical properties of concrete. The discussion concludes that geopolymers and mineral admixtures work efficiently in the mitigation of AAR if they are used in an appropriate percentage; they not only reduce/mitigate AAR but also significantly increase the mechanical properties of concrete.