Cement

• Ordinary Portland cement is obtained by mixing of calcareous materials (such as limestone /chalk) & argillacious material (clay/shale containing silica & alumina) burning the mixture in rotary kiln at very high temperature to produce clincker

Stages of manufacture of cement

1. Mixing of raw materials 2. Burning 3. Grinding

Raw materials-composition

Material Percentage (%)

Lime (Cao) 60 to 65

silica (SiO2) 20 to 25

Alumina (Al2O3) 3 to 8

Iron oxide (Fe2O3) 2 to 4

Magnesia (MgO) 1 to 4

Manufacture of cement

There are three main operations involved 1. Mixing of raw materials2. Burning3. Grinding

Mixing of raw materials

a.)Dry process b.)Wet process

In this method, the calcareous materials such as limestone &argillaceous materials such as clay are separated reduced in size of about 25mm in crushers. After drying, these materials are grounded in ball mills.This powder is then stored in hoppers.Then they are mixed in correct proportions.

Wet process