Composition of cement
- Cement is important binding material, and used in every type of construction activity.
- Composition of cement is nothing but elaboration of Ingredients of cement.
- For better understanding of cement composition, need to study some parameters in details.
- The percentage of cement ingredients varies and depend on the composition of cement, and important to achieve the quality of cement.
- Iron Oxide
- Calcium sulphate
What is Cement Made of – Composition of Cement
Ingredients Percentage in cement
- Lime 60-65
- Silica 17-25
- Alumina 3-8
- Magnesia 1-3
- Iron oxide 0.5-6
- Calcium Sulfate 0.1-0.5
- Sulfur Trioxide 1-3
- Alkaline 0-1
Functions of Cement Ingredients
The main features of these cement ingredients along with their functions and usefulness or harmfulness are given below:
o Lime is nothing but calcium oxides or calcium hydroxide
o It consists of 60-65% in cement
o The presence of lime in cement in sufficient quantity forms silicates and aluminates of calcium
o Lime should be in good proportion to imparts strength to cement.
o Less lime quantity reduces the strength of cement and may cause the cement to set quickly.
o Also the excess lime makes cement unsound.
o Excessive lime presence also cause expansion and disintegration of cement.
o Sillica in cement is also known as silicon dioxide.
o It should be present 17-25% in cement.
o Sufficient quantity of silica should be present in cement, and it forms dicalcium and tri calcium silicates in cement.
o Silica and its compound impart strength to cement.
o Alumina is knowns as Aluminium oxides.
o The chemical formula is Al2O3.
o Alumina is present 3-8% in cement.
o Alumina imparts the quick setting property of cement.
o Excess alumina weakens the cement.
o Magnesium is knows as magnesium oxides.
o The chemical formula is MgO.
o It should be present 1-3% in cement.
o Should not be present more than 3%.
o Magnesia in excess will reduce the strength of cement,
o Magnesia should not be present more than 2% in cement.
- Iron oxide:
o Chemical formula is Fe2O3.
o Iron oxide imparts color to cement.
o The percentage of iron oxide in cement is 0.5-6%
o It acts as a flux into the cement.
o At a very high temperature, it imparts into the chemical reaction with calcium and aluminum to form tricalcium alumino-ferrite.
o Tricalcium alumino-ferrite imparts hardness and strength to cement.
- Calcium Sulfate:
o Calcium sulfate is present in cement in the form of gypsum.
o The percentage of calcium sulfate in cement is 0.1-0.5%.
o Chemical formula is CaSO4
o Calcium sulfate in cement slow down or retard the setting time and action of cement.
- Sulfur Trioxide:
o Chemical formula for sulfur trioxide is SO3
o The percentage of sulfur trioxide in cement is 1-3%.
o It should not be present for more than 3%.
o Sulfur trioxide in excess make cemnt unsound.
- Alkaline: It should not be present more than 1%.
o Excess Alkaline matter causes efflorescence.
Chemical Formulas of Cement Materials
- Cement is made up of different compound, and all compounds as discussed above. Chemical composition of cement is depend on different compound used in cement . All the compounds or iIngredients of cement. imparts the characteristics of cement. There is no specific formula for cement, but for different components of cements as listed below,
- • Lime -Ca(OH)₂
- • Silica – SiO2
- • Alumina – Al2O3
- • Magnesia – MgO
- • Iron oxide – Fe2O3
- • Calcium Sulfate – CaSO4
- • Sulfur Trioxide – SO3
- • Alkaline – “X”(OH) 2