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.
4.	Composition of cement

Ingredients of cement.

  • Lime
  • Silica
  • Alumina
  • Magnesia
  • Iron Oxide
  • Calcium sulphate
Ingredients of cement

What is Cement Made of – Composition of Cement

There are eight major iIngredients of cement.. The following image is showing the ingredients of cement:

The general percentage of above mentioned Ingredients of cement.s given below,

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

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