Cement is an important binding material used in construction works. Cement is required for almost every construction work. Therefore, the composition of cement is of great interest to engineers.To understand cement structure or composition, one must know the functionality of cement components.By changing the quantity of a component during cement production, one can achieve the desired cement quality.

Composition of cement:

There are eight major components/ingredients of cement. The following image shows the ingredients of cement:



The general percentage of these materials in cement is given below:



Functions of cement components/ingredients:

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

1. Lime: Lime is calcium hydroxide or calcium oxide.

The presence of sufficient amount of lime requires silicates and aluminates of calcium.

Reduction in lime reduces the strength of cement property.

Reduction in lime causes cement to set quickly.

Excessive lime makes the cement unsound.

Excessive presence of lime causes cement to disintegrate and expand.


2. Silica: Silicon dioxide is known as silica, the chemical formula SiO2.

Sufficient amount of silica should be present in the cement to di-calcium and tri-calcium silicate.

Silica reinforces cement.

Silica typically represents a limit of about 30 percent cement.


3. Alumina: Alumina is aluminum oxide. The chemical formula is Al2O3.

Alumina provides quick setting properties to cement.

The presence of the expected amount of alumina leads to a lower clinkering temperature.

Excess alumina weakens cement.


4. Magnesia: Magnesium oxide. The chemical formula is MgO.

In terms of percentage,Magnesia should not be present more than 2% in cement.

Additional magnesia will reduce the strength of cement.


5. Iron oxide: The chemical formula is Fe2O3.

Iron oxide gives color to cement.

Acting as a flux.

At very high temperatures, it chemically reacts with calcium and aluminum to form tri-calcium alumino-ferrite.

Tricalcium alumino-ferrite provides hardness and strength to the cement.


6. Calcium Sulfate: The chemical formula is CaSO4

It is present in cement in the form of gypsum (CaSO4.2H2O)

It slows down quickly which inturn reduces the setting action of cement.


7. Alkaline:

It should not be more than 1%.

Highly alkaline substances cause efflorescence.


8. Sulfur trioxide: the chemical formula is SO3

In terms of percentage,it should not be present for more than 2%.

Cement becomes unsound due to excess sulfur trioxide. 






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