- Component materials:
Component materials required for cement making are Limestone, shale, slate, clay, chalk – Lime (60%), silica (20%), alumina (10%).
Iron oxide, magnesium oxide, sulphur trioxide, alkalies, carbon dioxide are also used as component materials in cement manufacturing.
- Constituents of cement:
75% is composed of calcium silicates. Rest is made up of Al2O3, Fe2O3 and CaSO4.
Di-calcium silicate (C2S) – 2CaO.SiO2 (15-40%)
Tri-calcium silicate (C3S) – 3CaO.SiO2 (35-65%)
Tri-calcium aluminate (C3A) – 3CaO.Al2O3 (0-15%)
Tetra-calcium alumino-ferrite (C4AF) – 4CaO.Al2O3..Fe2O3 (6 -20%)
Calcium sulphate (CaSO4) – (2%)
- Manufacturing process :
There are two processes for cement manufacturing.
- Wet methods.
- Dry methods.
In both methods raw materials are homogenized by casting, grinding and blending.
- Wet process:
Mix containing homogenized constituents and 30 – 40 % of water is heated to 1510 degree Celsius in a revolving (slightly) inclined kiln. Oxides of silica, calcium and aluminum combine to form cement clinkers. Mixed with calcium sulphate (gypsum) to reduce the rate of setting and crushed into powder in ball mills before storing in silos or bags.
- Dry process :
The homogenized mix is fed into the kiln and burned in a dry state. Other steps are the same as for the wet process. There is a considerable savings in fuel consumption, but workplace is dustier.