Composition of cement:
The two basic ingredients of cement are argillaceous and calcareous.
The composition of ordinary cement and ingredients are as follows:
|Ingredients||Normal range in %||Typical Composition %|
|4)Iron Oxide (Fe2O3)||0.5 – 6%||3|
|6)Sulphur Trioxide (SO3)||1-3%||1|
|7)Soda or potash||0.5 – 1.3%||1|
|8)Calcium sulphate (CaSo4)||3 – 5%||4|
For better understanding watch the video:
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:
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%
- 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 it’s setting time.
- Its percentage is between 17 -25 %
- 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%
5. Magnesium oxide:
- It provides hardness and colour to the cement when present in small quantity.
- The magnesium oxide in excess quantity makes the cement unsound.
6. Sulphur trioxide:
- It makes the cement sound, when present in very small quantity.
- If it is used in excess it produces expansion of cement thus making it unsound and also excess of 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:
1. Alkali oxides.
2. Magnesium oxide.
If the amount of alkali oxides exceeds 1%. it leads to the failure of concrete made from that cement. If the content of magnesium oxide exceeds 5%, it causes cracks after mortar or concrete hardens.