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Raw materials used for manufacturing of Portland cement are found naturally in the earth crust. It is made primarily from calcareous materials, argillaceous materials and gypsum. Calcareous materials containing limestone or chalk and argillaceous materials containing an oxide of silica-alumina and iron are found as clay or shale.
Also Read: Dry Process for Manufacturing of Cement
Limits of Main Chemical and Oxide Constituents of OPC are Given in Below Table:
|Sr. No.||Constituents||Percent Content (%)|
|04.||Iron Oxide (Fe2O3)||
|05.||Magnesium Oxide (MgO)||
|06.||Sulphur Trioxide (SO3)||
|07.||Alkalies (K2O, Na2O)||
Functions of the Constituents of OPC:
It is the main constituent for manufacturing of cement which imparts cementing property to cement. An excess quantity of lime causes expansion and disintegration of cement. Deficiency in lime causes decrease in strength and the cement set quickly. If it is in right proportion, it makes the cement sound and strong.
This play a major role in imparting strength to concrete. Silica undergoes the chemical reaction with calcium to form dicalcium silicate (C2S) and tricalcium silicates (C3S). Excess silica adds strength to cement but it prolongs the setting time.
This forms complex compounds with silica and calcium to impart setting property of cement. It acts as a flux and lowers the clinkering temperature. Use of an excess amount of alumina quickens setting time but reduces the strength of cement.
04. Iron Oxide:
This is mainly responsible for imparting colour to cement. The hardness and strength is also improved to a certain extent. It helps in the fusion of raw materials during the manufacture of cement.
05. Magnesium Oxide:
It imparts strength when mixed in small quantity but excess amount makes the cement unsound.
06. Sulphur Trioxide: This makes the cement sound if present in small quantity but excess amount makes the cement unsound.
This makes the cement sound if present in small quantity but excess amount makes the cement unsound.
Cement is sometimes blended with other cementitious and/or special material. These cements are called blended cement which is produced by intimately blending two or more types of cementitious materials. Generally, the primary blending materials are fly ash, ground granulated blast furnace slag (GGBS), silica fume, natural pozzolana etc.