Functions of Various Ingredients of Cement

1.Lime:It is very important in cement.It forms about 63 percent of cement. The nature of cement depends on it.Defeciency in lime reduces the strength of cement and cause it to set quickly. Again excess cause cement unsound and cause disintegration and expantion.

2.Silica:It is another important compound. It imparts strength to concrete.

3.Alumina:It imparts quick setting property of cement. Clinkering temperature is lowered by adding of alumina.

4.Magnesia:It should not present in cement more than 2 percent.Excess reduce strength.

5.Iron oxide:It imparts the color of cement. At high temperature it goes to a chemical reaction with calcium and aluminium and forms tetracalcium aluminofferrite which imparts hardness and strength.


6.Salphur tri oxide:It should not present more than 2 percent.Excess cause cement to be unsound.

7.Calcium sulphate:It is present in cement in the form of gypsum.It retards the setting of cement.

8.Alkalies: It should not present more than 1 percent.Excess cause efflorescence.

Constituents of Cement

Constituents of cement are mainly two types
1.Mineral constituents , 2.Acid and Alkaline constituents.

Mineral Constituents

       Name                   Oxide compositions   Abbreviation    Percentage(%)

Tricalcium Silicate ~     3CaO.SiO2(*1) ~            C3S(*1) ~              45~55
Dicalcium Silicate ~      2CaO.SiO2(*1) ~            C2S(*1) ~              20~30
Tricalcim Aluminate ~    3CaO.Al2O3 ~                      C3A ~                        9~13
Tetracalcium 
Aluminoferrite ~              4CaO.Al2O3.Fe2O3~             C4AF  ~                 8~20
Calcium Sulphate~          CaSo4  ~                                  ----------        ~            2~6
Other Compounds~        ----------   ~                               ---------   ~                  2~8       

Acid and Alkaline Constituents
        
        Name               Composition                Range of percentage


Calcium oxide     ~     CaO               ~               60~67
Magnesium oxide~     MgO               ~               0.1~4
Silica                    ~     SiO2                  ~                  17~25
Alumina               ~     Al2O3                ~                   3~8
Iron oxide             ~     Fe2O3               ~                  0.5~6
Sulphur trioxide   ~     SO3                    ~                  1~3
Potassium oxide   ~     K2O                   ~                   0.3~1
Sodium oxide       ~      Na2O                ~                   0.4~1.3
Loss on Ignition   ~      --------            ~              1.8~2
Insoluble Resedue ~     --------           ~              0.3~0.5