Bricks are the most commonly used construction material. Bricks are prepared by moulding clay in rectangular blocks of uniform size and then drying and burning these blocks. In order to get a good quality brick, the brick earth should contain the following constituents.
Brick earth should contain about 50 to % of silica.
It is responsible for preventing cracking, shrinking and warping of raw bricks.
It also affects the durability of bricks.
If present in excess, then it destroys the cohesion between particles and the brick becomes brittle.
Good brick earth should contain about 20% to 30% of alumina.
It is responsible for plasticity characteristic of earth, which is important in moulding operation.
If present in excess, then the raw brick shrink and warp during drying.
The percentage of lime should be in the range of 5% to 10% in a good brick earth.
It prevents shrinkage of bricks on drying.
It causes silica in clay to melt on burning and thus helps to bind it.
Excess of lime causes the brick to melt and brick looses its shape.
4. Iron oxide
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 blakish.
If the quantity of iron oxide is comparatively less, the brick becomes yellowish in colour.
Good brick earth should contain less a small quantity of magnesia about1%)
Magnesium in brick earth imparts yellow tint to the brick.