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