Kaolin is a naturally occurring pozzolan that stems from clay that contains a high percentage of kaolinite (Al2O3.2SiO2.2H2O).

The properties of clays vary considerably, and they strongly depend on their composition and mineral structure. The main characteristic that determines the usefulness of kaolin for a large number of applications is its mineral purity. Thermal treatment allows for dehydroxylation of the kaolinite’s crystal structure into a highly reactive amorphous material suitable to be used as a Supplementary Cementitious Material.

Cement hydration allows calcined kaolin to react with the calcium hydroxide to form compounds with cementitious properties including C-S-H (hydrated calcium silicates) and stratlingite (hydrated calcium aluminosilicates).

Application and Uses

By including calcined kaolinite in portland cement, increased compressive strengths and decreased permeability may result. As a SCM, kaolin can reduce the environmental impact generated by the cement manufacture, improve the physical, chemical and mechanical properties of blends, and reduce costs in the concrete industry.