OPC is produced by inter-grinding clinker, performance improver and gypsum in a cement mill. Portland cement is a blend of finely pulverized clinker, produced by burning at high temperature material containing lime, alumina, iron and silica in pre determined proportion to give the desired end proportion. Normally Gypsum or its derivatives are added during grinding stage for set control. When mixed with water alone or in combination with sand and stone, it has the property of combining slowly with water to form hard mass.

The two principal raw materials used in the manufacture of Portland Cement are calcareous materials such as lime stone, chalk, shells or marl and argillaceous materials such as clay and shalo (rich in silica).

The raw material i.e. calcareous and argillaceous with correctives are finely sound and intimately blended and fined in a rotary kiln at high temperature of 14500 - 15000 C.  The material which is coming out of kiln is called Clinker. The clinker is then cooled and grind to fine powder along with small quantity of Gypsum (1% to 5%) to give Portland Cement.

Portland Cement when mixed with enough water, the compound present in cement react with water to form a cementations crystalline structure which adheres to the sand and aggregates. This binds the mass together and with growing strength till it become very hard. OPC is produced by inter-grinding clinker, performance improver and gypsum in a cement mill.

OPC is further classified, as relevant in our case as, 43 Grade and 53 Grade OPC.