Cement's Constituents

Cement basically constitute of two different types of components ARGILLACEOUS (Clay) and CALCAREOUS (Calcium Carbonate) compounds.

Constituents of Cement: 

Lime CaO  --------------------------------------62-65%
Silica SiO2 --------------------------------------17-25%
Alumina Al2O3 --------------------------------3-8%

Calcium Sulphate CaSO4--------------------3-4%
Iron Oxide Fe2O3 -----------------------------3-4%
Magnesia MgO ---------------------------------1-3%
Sulphur trioxide SO3 -------------------------1-3%
Alkalies Na2O, K2O --------------------------0.2-1%

Functions of Constituents:

1. Lime CaO: Imparts Strength, Soundness if excess amount cause expands and disintegration in cement. if deficiency reduces strength, set quickly.
2.  Silica SiO2  :  Increase strength, excess amount causes delay in setting time.

3. Alumina Al2O3 : imparts quick setting, act as flux, reduce clinkering temp. during burning of cement, excess amount weakens the cement

4.Calcium Sulphate CaSO4: added in the form of gypsum, increase initial setting time of cement.

5. Iron Oxide Fe2O3 : impart color, strength, hardness to cement, reddish brown tint, toughness to cement.

6. Magnesia MgO : Color and hardness to cement, yellowish tint, excess amount makes cement unsound.

7. Sulphur trioxide SO3 : soundness to cement

8. Alkalies Na2O, K2O : efflorescence and staining to structures, white gray spots, react with reactive silica form gels. which leads to formation of cracks.