Portland cement, the basic ingredient of concrete, is a closely controlled chemical combination of calcium, silicon, aluminium, iron and small amounts of other ingredients to which gypsum is added in the final grinding process to regulate the setting time of the concrete. Lime and silica make up about 85% of the mass. Common among the materials used in its manufacture are limestone, shells, and chalk or marl combined with shale, clay, slate or blast furnace slag, silica sand, and iron ore.

Each step in manufacture of portland cement is checked by frequent chemical and physical tests in plant laboratories. The finished product is also analyzed and tested to ensure that it complies with all specifications.

Different Steps for Portland Cement Manufacturing Process:-

1. Collecting the Ingredients: Lime, silica and alumina are the three basic ingredients of cement. The source of the lime is limestone. Silica is obtained from clay, and alumina is obtained from bauxite.
2. Grinding the Ingredients: The ingredients are grinded to make them small enough to pass a sieve of size 200. The grounded ingredients are then mixed homogeneously.
3. Making Clinkers: The grinded mixture is then fed into a inclined tubular kiln for roasting. Temperature of this roasting kiln is around 1500 to 1700 degree centigrade. During the process of roasting, Silica, alumina and lime are converted into calcium aluminates. The ingredients take the shape of small lumps called clinker.
4. Cooling the Clinkers: The hot clinkers cannot be used directly for the further processing. The clinkers are stored for cooling to a temperature of 50 to 55 degree centigrade.
5. Grinding the Clinkers: The clinkers then need to be finely grinded to make cement. While grinding, 2 to 5 percent gypsum to be added. Gypsum retards the setting time of the cement upon mixing it with water.
6. Storage and Packing: The cement is then stored in large silos until weighing and packing. Packed cement is then supplied to market.

Portland cement manufacturing is a large scale process. The quality of the final manufactured cement depends upon the proportion of the ingredient and maintaining proper process parameters. To ensure the end quality, a strict quality check is maintained throughout the entire Portland cement manufacturing process.