Pozzolans

Pozzolans are materials that are not themselves cementitious, but contain constituents that will combine with lime at ordinary temperatures in the presence of water to form stable insoluble hydraulic compounds. Pozzolans have been subjected to heat either naturally (volcanic earth) or artificially (crushed fired clay brick and tile). Heating has resulted in certain constituents, principally silicates and aluminates, becoming reactive towards alkalis. When mixed with lime, hydraulic compounds are produced by the reaction between these constituents and the lime.