14 - Alkali-Aggregate Expansion and Corrosion Inhibiting Admixtures

Abstract

The alkali-aggregate expansion (AA) involves chemical interaction between alkali hydroxides, usually derived from cement and reactive components in the aggregate particles. In addition to alkali-silica and alkalicarbonate expansion reaction, a third type referred to as alkali-silicate reaction in concrete containing argillite and greywacke is proposed, and this reaction is generally slow and the mechanism is not completely worked out. Regardless of the type of rock or mineral, increases in expansion are influenced by alkali content, water, temperature, and time of exposure. Not all aggregates are reactive and such aggregates may be the right choice. However, there are reactive and marginally reactive aggregates which promote good mechanical properties in concrete that may be available in close proximity to the construction activity and may have to beused. Use of low alkali cement and blending with additives may be needed with such aggregates. It is generally acknowledged that below a specific amount of alkali per cubic meter of concrete made with a reactive aggregate, very little expansion takes place.