Alkali-aggregate reaction (AAR) is an overarching term for two types of premature concrete deterioration: alkali-silica reaction (most common) and alkali-carbonate reaction (less common). These forms of deterioration involve a chemical reaction between CERTAIN aggregate types and the internal pore solution in concrete. The chemical composition of the cementitious materials (main) and the aggregates (to a lesser extent) dictate the composition of the pore solution and thus the aggregate reactivity. In the presence of moisture this reaction may result in deleterious expansion and cracking and can ultimately limit the service-life of the affected concrete.