Composition of cement

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.

Ingredients of cement.

• Lime
• Silica
• Alumina
• Magnesia
• 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:

1. Lime:
   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.
2. Silica:
   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.
3. Alumina:
   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.
4. Magnesia:
   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.
5. 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.
6. 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.
7. 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.
8. 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