Cement is the basic and the most widely used building material. Twice as much Cement/Concrete is used worldwide than all other Building Materials.
A Mixture of Limestone and Clay is ground and burnt at a very high temperature to form Clinker. The Clinker is ground to a fine powder with addition of Gypsum ( up to 5 %) to form Cement. The essential components of Cement are Lime, Silica, Alumina and Iron Oxide.
There are different types of Cement , which differ based on their chemical composition. However, the manufacturing process remains the same.
Cement - Varieties
There are different varieties of cement based on different compositions according to specific end uses, namely, Ordinary Portland Cement, Portland Puzzolona Cement, White Cement, Portland Blast Furnace Slag Cement and Specialized Cement.
The basic difference lies in the percentage of clinker used.
Ordinary Portland cement (OPC)
OPC, popularly known as grey cement, has 95 per cent clinker and 5 per cent gypsum and other materials. It accounts for 70 per cent of the total consumption.
Portland Puzzolona Cement (PPC)
PPC has 80 per cent clinker, 15 per cent Pozzalona and 5 per cent gypsum and accounts for 18 per cent of the total cement consumption. It is manufactured because it uses fly ash/burnt clay/coal waste as the main ingredient.
White cement is basically OPC - clinker using fuel oil (instead of coal) with iron oxide content below 0.4 per cent to ensure whiteness. A special cooling technique is used in its production. It is used to enhance aesthetic value in tiles and flooring. White cement is much more expensive than grey cement.
Portland Blast Furnace Slag Cement (PBFSC)
PBFSC consists of 45 per cent clinker, 50 per cent blast furnace slag and 5 per cent gypsum and accounts for 10 per cent of the total cement consumed. It has a heat of hydration even lower than PPC and is generally used in construction of dams and similar massive constructions.
Oil Well Cement is made from clinker with special additives to prevent any porosity.
Rapid Hardening Portland cement
Rapid Hardening Portland Cement is similar to OPC, except that it is ground much finer, so that on casting, the compressible strength increases rapidly.
Water Proof Cement
Water Proof Cement is similar to OPC, with small portion of calcium stearate or non- saponifibale oil to impart waterproofing properties.