COMPOSITIONS OF ORDINARY CEMENT
A typical chemical analysis of a good ordinary cement along with the desired range is given below-
S.No.
|
INGREDIENTS
|
PERCENTAGE RANGE
|
1
|
Lime (CaO)
|
60 - 67
|
2
|
Silica (SiO2)
|
17 - 25
|
3
|
Alumina (Al2O3)
|
3 - 8
|
4
|
Calcium
Sulphate (CaSO4)
|
3 - 4
|
5
|
Iron Oxides (Fe2O3)
|
3 - 4
|
6
|
Magnesia (MgO)
|
1 - 3
|
7
|
Sulphur (S)
|
1 - 3
|
8
|
Alkalies
|
0.2 - 1
|
FUNCTIONS OF CEMENT INGREDIENTS
1. Lime (CaO):
- This is the important ingredient of cement and its proportion is to be carefully maintained.
- Presence of lime in sufficient quantity is required to form silicate and aluminates of calcium.
- Deficiency in lime reduces the strength and causes cement to set quickly.
- Excess lime make cement unsound.
- Excess lime causes cement to expand and disintegrated.
2. Silica (SiO2):
- Impart strength due to the formation of dicalcium and tricalcium silicates.
- If silica in excess the strength of cement increase but at same time its setting time is prolonged.
3. Alumina (Al2O3):
- Impart quick setting property to cement.
- It acts as flux and lower the clinkering temperature.
- Excess alumina weakens the cement.
4. Calcium Sulphate (CaSO4):
- It is present in the form of gypsum.
- Increases initial setting time of cement.
5. Iron Oxides (Fe2O3):
- Impart colour to cement
- Tricalcium alumino ferrite imparts hardness and strength.
6. Magnesia (MgO):
- If present in small quantity impart hardness and colour to the cement
- Excess magnesia makes the cement unsound and reduces its strength.
7. Sulphur (S):- Should not present more than 2 percent.
- Excess sulphur causes cement unsound.
8. Alkalies:
- Should not present more than 1 percent.
- Excess alkaline matter in cement causes number of troubles such as efflorescence, alkali-aggregate reaction, and staining when used in concrete, brickwork or masonry mortar.
