Bricks Classification is done in order to distinguish between bricks so that they can be used accordingly. Indian Standard is followed in this article to classify bricks. Special type of bricks known as “fire bricks” are covered separately at the end.
These are blocks of tampered clay, moulded to suitable shapes and sizes while it is still in plastic condition , dried in sun and burnt so as to make them strong, hard and durable.
As per Indian Standard IS: 1077-1957, the bricks are classified as under
1) First Class Bricks (Class 1)
Class 1 bricks have uniform color, thoroughly burnt and plane rectangular faces with parallel sides and sharp straight right angled edges. They would have fine, compact and uniform texture and emit a clear ringing sound when struck with each other
2) Second Class Bricks (Class 2)
They have uniform color and may be slightly over-burnt. These bricks may be slightly distorted and have round edges. They should have fine, compact, uniform texture and emit a clear ringing sound when struck with each other.
3) Third Class Bricks (Class 3)
They may be over-burnt or under burnt. They may be distorted and have round edges. The defect in uniformity and shape should not be such as to cause difficulty in obtaining uniform courses with their use.
Water Absorption Of Bricks
The water absorption of bricks after 24 hours immersion in cold water should be as given below considering bricks classification done earlier.
- First Class Bricks – 20% by weight
- Second Class Bricks – 22% by weight
- Third Class Bricks – 25% by weight
Fire Bricks are made of “fire clay” or “refractory clay” and burnt at high temperatures in special klins. These bricks are used for the lining of furnances, boilers, combustion chambers and chimneys where high temperature exists. These are generally capable of withstanding high temperatures upto 1700° C.
The usual composition of fire clay is
- Slica = 56 to 90%
- Alumina = 2 to 36%
- Iron Oxide = 2 to 6%
- Lime, magnesia, potash and soda = 8 to 20%