Functions of Cement Ingredients

Functions of Cement Ingredients

The main features of these cement ingredients along with their functions and usefulness or harmfulness are given below:

1. Lime: Lime is calcium oxide or calcium hydroxide.
• Presence of lime in a sufficient quantity is required to form silicates and aluminates of calcium.
• Deficiency in lime reduces the strength of property to the cement.
• Deficiency in lime causes cement to set quickly.
• Excess lime makes cement unsound.
• Excessive presence of lime cause cement to expand and disintegrate.
2. Silica:Silicon dioxide is known as silica, chemical formula SiO₂.
• Sufficient quantity of silica should be present in cement to dicalcium and tricalcium silicate.
• Silica imparts strength to cement.
• Silica usually presents to the extent of about 30 percent cement.
3. Alumina: Alumina is Aluminium oxide. The chemical formula is Al₂O₃.
• Alumina imparts quick setting property to the cement.
• Clinkering temperature is lowered by the presence of the requisite quantity of alumina.
• Excess alumina weakens the cement.
4. Magnesia: Magnesium Oxide. Chemical formula is MgO.
• Magnesia should not be present more than 2% in cement.
• Excess magnesia will reduce the strength of the cement. 
5. Iron oxide: Chemical formula is Fe₂O₃.
• Iron oxide imparts color to cement.
• It acts as a flux.
• At a very high temperature, it imparts into the chemical reaction with calcium and aluminum to form tricalcium alumino-ferrite.
• Tricalcium alumino-ferrite imparts hardness and strength to cement.
6. Calcium Sulfate: Chemical formula is CaSO₄
• This is present in cement in the form of gypsum(CaSO₄.2H₂O)
• It slows down or retards the setting action of cement. 
7. Sulfur Trioxide: Chemical formula is SO₃
• Should not be present more than 2%.
• Excess Sulfur Trioxide causes cement to unsound. 
8. Alkaline:
• Should not be present more than 1%.
• Excess Alkaline matter causes efflorescence.