ABSTRACT
Aggregates in concrete are generally considered to be inert. Under certain conditions, however, some components in aggregates, especially siliceous minerals, may react with the sodium and potassium hydroxides in the alkaline pore solution of concrete. A gel is formed which can imbibe water. The reaction products have a molar volume in excess of the reactants, which leads to swelling. The resultant pressures cause expansion of the hardened concrete and, if the tensile strength of the concrete is exceeded, extensive cracking may become apparent on the surface. This phenomenon is known as alkaliaggregate reaction (AAR).
