Portland cement

Cement made by burning together, in a kiln, a mixture of limestone and clay to form a clinker rich in calcium silicates. This is ground to a fine powder with a small proportion of gypsum which regulates the rate of setting when cement is mixed with water. Calcining occurs at temperatures in excess of 750°C and clinkering at +1,450°C. There are several types of Portland cement including: ordinary, rapid-hardening, sulphate-resisting and white.