What are the essential steps required in the manufacture of cement ?

The ingredients used for making cement are limestone, that is calcium carbonate (CaCO₃) and clay, which consists of silica (SiO₂), alumina (Al₂O₃) and ferric oxide (Fe₂O₃).

Manufacture of cement

The following steps are involved in the manufacture of cement.

1. Limestone and clay are crushed to a fine powder.

2. They are blended in the desired proportion.

3. The mixture is poured into the upper end of a slow-turning cement kiln and heated to about 1500⁰C.

4. The following reactions take place inside the kiln.

Calcium carbonate decomposes to form calcium oxide which combines with alumina and silica.

Note that chemically, cement is a mixture of calcium aluminate and calcium silicate (formed on adding water).

5. The mixture (cement) solidifies into limps about the size of a pea, called clinkers.

6. Clinkers are then mixed with gypsum (it delays the setting of cement).

7. These are then ground into a fine powder.