Describe the Manufacture of Portland Cement

Portland cement

In 1824, Joseph Aspdin (UK) discovered Portland cement.

Portland cement is chemically defined as a finely ground mixture of calcium aluminates and silicates of varying compositions, which hydrates on mixing with water to form a rigid solid structure.

A strongly heated mixture of lime, stone and clay, when mixed with small amount of water, sets in few hours to form a hard stone-like substance.

This hard stone-like substance resembles Portland rock of England and hence named as Portland cement.

Chemical composition of cement

Percentage of various ingredients for the manufacture of Portland cement should be as follows:

Ingredient	Proportion (%)
Lime $(CaO)$	62
Silica $(SiO 2)$	22
Alumina $(Al 2 O 3)$	5
Calcium sulphate $(CaSO 4)$	4
Iron oxide $(Fe 2 O 3)$	3
Magnesium oxide $(MgO)$	2
Sulphur trioxide $(SO 3)$	1
Alkalies	1

Characteristics of cement

(i) The colour of cement should be uniformly grey with greenish shade.

(ii) It should feel smooth when touched or rubbed.

(iii) It should be free from any hard lumps.

(iv) It should not contain excess silica, lime, alumina or alkalies.

Properties of cement

A good cement possesses the following properties:

It provides strength to masonry.
It stiffens or hardens early.
It possesses good plasticity.
It is an excellent building and binding material.
It is easily workable.
It has good moisture resistance.

Uses of cement

Following are the various uses of cement:

It is used in cement mortar for masonry work, plastering, pointing etc.
It is used in the manufacture of joints for pipes, drains etc.
It is used in concrete for laying floors, roofs and constructing lintels, beams, stairs, pillars etc.
It is used in the construction of engineering structures such as bridges, culverts, dams, tunnels, light houses etc.
It is used in the preparation of foundations, water-tight floors, footpaths etc.
It is employed for the construction of wells, water tanks, tennis courts, lamp posts, telephone cabins, roads etc.