Role of Gypsum in Cement

Gypsum is a soft sulfate mineral composed of calcium sulfatedihydrate, with the chemical formula CaSO4·2H2O. It is used for a variety of manufacturing, industrial and agriculture uses. The colour of gypsum is white, grey, brown and red. When the production process of cement, clinkers are formed and gypsum is added when it is cooled down then the mixture sent to final grinding process. For ordinary Portland cement it uses upto 3-4% and for quick setting cement it can be reduced to 2.5%. Role of gypsum in Cement When water is added into cement hydration process starts, water reacts with C3A and hardens. This process occurs very quickly and doesn’t allow time for transporting, mixing and placing. So Gypsum is used to slow down the hydration process. When gypsum is added into the cement and water is added to it, reaction with C3A particles tales place to form ettringite. This ettringite is initially formed as very fine-grained crystals, which form a coating on the