In order to get good quality brick, the earth should contain the following constituents.- Silica
- Alumina
- Lime
- Iron Oxide
- Magnesia
1. SILICA
- Good brick earth should contain about 50 to 60% of Silica
- It prevents Cracking, Shrinkage and Warping of raw bricks.
- It also affects the durability of bricks.
- The excess of silica destroys the cohesion between particles and the brick becomes brittle.
- The percentage of alumina should be in the range of 20 to 30% in a good brick earth.
- The presence of this constituent imparts plasticity to the clay so that it can be moulded.
- If present in excess, then the raw bricks shrink and warp during drying.
3. LIME
- Brick earth should contain about 2 to 5% of lime.
- It prevents shrinkage of raw brick on drying.
- It helps to lower the fusion temperature.
- It cause silica in clay to melt on burning and thus helps to bind it.
- The excess of lime causes the bricks to melt and brick looses its shape.
4. IRON OXIDES
- A good brick earth should contain about 5 to 7% of Iron oxide.
- It gives red colour to the bricks.
- It improves impermeability and durability.
- It gives strength and hardness.
- If present in excess, then the colour of brick becomes dark blue or blackish.
- If the quantity of iron oxide is comparatively less the brick becomes yellowish in colour.
5. MAGNESIA
- Good brick earth should contain a small quantity of magnesia about 1%.
- Magnesium in brick earth impart yellow tint to the brick.
- It is responsible for reducing shrinkage.
- Excess of magnesia leads to the decay of bricks.
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Silica........................................50-60%
Alumina...................................20-30%
Lime.........................................2-5%
Iron oxide.................................5-7%
Magnesia..................................not more than 1%
