Composition of cement:

The composition of ordinary cement and ingredients are as follows:

 

 

Ingredients	Normal range in  %	Typical Composition             %
1)Lime (Cao)	60-70%	62
2)Silica (SiO2)	17-25%	22
3)Alumina (Al2O3)	3-8%	5
4)Iron Oxide (Fe2O3)	0.5 – 6%	3
5)Magnesia (MgO)	0.1-4%	2
6)Sulphur Trioxide (SO3)	1-3%	1
7)Soda or potash	0.5 – 1.3%	1
8)Calcium sulphate (CaSo4)	3 – 5%	4
	Total	100

Also Read: Interview question process of Manufacturing of cement Most repeated and imp Hydration of cement

Functions of ingredients of cement and average composition of cement:

1. Lime:

It is a major ingredient of cement and constitutes about two-thirds of cement

• It makes the cement sound and strong.

 

• The lime in excess quantity makes cement unsound and causes the cement to disintegrate.

 

• If lime is low in quantity, the mix will be improper which will lead to low strength once as this cement will set quickly.

 

• Lack of lime will reduce the strength of cement.

 

• Its percentage is between 60-70%

 

2. Silica:

• It is an important ingredient of cement and imparts strength to the cement due to the formation of dicalcium and tricalcium silicates.

 

• Silica in excess provides greater strength to the cement but at the same time prolongs its setting time.

 

• Its percentage is between 17 -25 %

 

 

3. Alumina:

• It provides quick setting property to the cement.

 

• It acts as a flux and lowers the clinkering temperature.

 

• Alumina in excess reduces the strength of cement.

 

• Its composition in cement is between 3-8%

 

4. Iron oxide:

• It provides colour, hardness and strength to the cement.

 

• It also helps the fusion of raw materials during the manufacture of cement.

 

• Its composition in cement is between 0.5 – 6%

 

• It provides hardness and colour to the cement when present in small quantities.

 

• The magnesium oxide in excess quantity makes the cement unsound.

 

• It makes the cement sound, when present in very small quantities.

 

• If it is used in excess it produces expansion of cement thus making it unsound and also an excess sulphur trioxide increases the setting time.

 

7. Alkalies(Soda and Potash):

• These are used in the form of soda and potash.

 

• These should be present in small quantities.

 

• The alkalies in excess quantity will cause efflorescence.

 

• The average composition is about 1%

 

8. Calcium sulphate:

• It is about 3% of the cement and is added in the form of gypsum during the process of grinding of clinker
• It is a retarder since it increases the initial setting time of cement.
• If gypsum is not added the cement will set at the moment water is added to it, without giving any time for mixing and placement.

 

Harmful ingredients of cement:

The following are the two ingredients which affect the quality of cement: