Saturday, 6 April 2019

Function of cement ingredients


1. Lime  ( CaO)  :  Excess lime makes the cement unsound and causes the cement to expand and disintegrate. Deficiency in lime makes loss of strength and makes cement to set quickly.

2. Silica (SiO2 ) : It imparts the strength to cement by forming the Di-calcium and Tri- calcium silicates. Excess silica makes the strength of cement increases, but prolong the setting time.

3. Alumina ( Al2O3) : It imparts quick setting property to the cement. It acts as a flux and lowers the clinkering temperature. Excess alumina makes cement weaker.

4. Calcium sulphate ( CaSo4) : It is in the form of gypsum and increases the initial setting time of cement.

5. Iron Oxide ( Fe2O3) : It imparts colour, hardness and strength to cement.

6. Magnesia ( MgO) : It imparts hardness and colour if present in small amount. Excess Mgo make cement unsound.

7. Sulphur( S) : It is useful in making sound cement.

8. Alkalies : Most of the alkalis present in the raw materials are carried away by the flue gases during heating process . presence of alkalies cause problem such as alkali- aggregate reaction, efflorescence and staining etc.

The above mentioned constituents in chemical reaction form the following compound called 'bogue's compounds'.

Tri- calcium silicate ( Alite)
C3S
45%
Di- calcium Silicate ( Belite )
C2S
25 %
Tri- calcium Aluminates ( Celite)
C2A
11 %
Tetra - calcium Alumino ferrite ( Felite )
C4AF
9 %

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