Cement

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Cement.

Portland Cement

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.

Concrete

• 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”.