Clinker is the basic, raw material used in the production of all types of cement and the one that bestows upon cement its hydraulic properties. Clinker is obtained by burning a mixture of approximately 80% of limestone and 20% of clay at high temperatures through chemical reactions; clinker occurs as spheroidal nodules 10-25mm in diameter, with high hardness. The quantity of clinker in cement could be reduced by adding alternative materials, called cement additives.