GA Study Notes On Cement Manufacturing

Manufacturing of Cement

Cement is essential for construction activity such as building houses, factories, bridges, roads, airports, dams and for other commercial establishments.The first cement plant was set up in Chennai in 1904.It was discovered by an English Mason, Joseph Aspdin in 1824. He called it Portland cement because he thought that it resembled the limestone found in Portland.

Approximate Composition of Portland cement
Calcium oxide (CaO) 60-70%
Silica (SiO₂) 20-25%

Alumina (Al₂O₃) 5-10%

Ferric oxide (Fe₂O₃ )         2-3%

Raw materials are:

Limestone -  (provides lime), Clay -  (provides alumina and silica), Gypsum - (reduces the setting time of cement).

For a good quality cement, the ratio of silica (SiO) to alumina Al₂O₃) should be between 2.5 and 4 and the ratio of lime (CaO) to the total of the oxides of silicon (SiO₂) aluminium (Al₂O₃) and iron (Fe₂O₃) should be as close as possible to 2.

The raw materials for the manufacture of cement are limestone and clay. When clay and lime are strongly heated together they fuse and react to form ‘cement clinker’. This clinker is mixed with 2-3% by weight of gypsum (CaSO₄·2H₂O) to form cement.Thus important ingredients present in Portland cement are dicalcium silicate (Ca₂SiO₄) 26%, tricalciumsilicate (Ca3SiO5) 51% and tricalcium aluminate (Ca₃Al₂O₆)11%.Mortar is a mixture of cement, sand, and water. It is used for plastering walls and binding bricks and stones.Concrete is a mixture of cement, sand, gravel or small pieces of stone and water. It is used for the construction of floors.RCC - The structure having iron rods embedded in wet concrete, is known as reinforced concrete. 

Setting of Cement: When mixed with water, the setting of cement takes place to give a hard mass. This is due to the hydration of the molecules of the constituents and their rearrangement. The purpose of adding gypsum is only to slow down the process of setting of the cement so that it gets sufficiently
hardened.It is an exothermic process, therefore cement structures have to be cooled up to 7 days by sprinkling water.

Uses: Cement has become a commodity of national necessity for any country next to iron and steel. It is used in concrete and reinforced concrete, in plastering and in the construction of bridges, dams, and buildings.