The reactions between alkalis and certain mineral constituents in some aggregates may result in expansion within the concrete and consequent cracking. Different terms are used to describe these deleterious reactions, such as Alkali-silica reaction, Alkali-silicate reaction and Alkali-carbonate-rock reaction.

Generally, its effect can be reduced or eliminated by careful selection of lower alkali cement to use with potentially alkali reactive aggregate. The alkali content of cement is usually expressed as a percentage of acid-soluble sodium oxide (Na₂O) equivalent by mass of cement. GIC OPC is as low as 0.3-0.4%. When considering concrete as a whole, the alkali content is expressed in terms of kilograms per cubic meter, kg/m³.