Portland Cement

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The approximate composition of Portland Cement is :

  • Calcium Oxide → 62%
  • Silica → 22%
  • Alumina → 7.5%
  • Magnesia → 2.5%
  • Ferric Oxide → 2.5%

The above compounds are provided by the two raw materials :

  • Lime Stone
  • Clay

In cement almost entire amount of lime is present in combined state as calcium silicates and calcium aluminates.

Note :

  • Cement containing excess amount of lime cracks during setting while cement containing less amount of lime is weak in strength. Setting of cement is an exothermic process.
  • A small amount of gypsum is added to slow down the setting of cement.
  • Cement with excess of silica shows slow setting and that having an excess of alumina shows quick setting.
  • Cement containing no iron is white but hard to burn.


  • It is a mixture of cement, sand, gravel (small pieces of stones) and approximate amount of water.
  • When the cement concrete is filled in and around a wire – netting or skeleton of iron rods and allowed to set the resulting structure is known as “Reinforced – Concrete”.

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