Chemical Constituents of Cement

While manufacturing of Portland Cement the following ingredients are in following Proportion:

Ingredient	Proportion
Lime (CaO)	63.0%
Silica (SiO2)	22.0%
Alumina (Al2O3)	6.0%
Iron Oxide(Fe2O3)	3.0%
Magnesium Oxide (MgO)	2.50%
Sulphur trioxide (SO3)	1.75%
Loss on ignition	1.50%
Insoluble residue	0.25%

Besides the above ingredients , calcium sulphate (CaSO4),commonly known as gypsum is also added by 3 to 4%.It helps for controlling the initial settling time of cement.