On field practice
Clay bricks are classified as first class, second class, third class and fourth class based on their physical and mechanical properties.
First class bricks
1. The completely burned and are of deep red, cherry or copper color .
2. Square and rectangular surfaces, straight edges and sharp corners should be smooth and parallel.
3. These should be free of cracks and stones.
4. They should have a similar composition.
5. With an impression of a zero- one nail is kept in the brick.
6. Fractured surface of the brick and limestone lumps should not show.
7. The two bricks are struck against each other should be a metallic or ringing sound.
8. Submerged in cold water for 24 hours, the water absorption of the dry weight should be 12-15 %.
9. Crushing strength of the brick must be less than 10 N/mm2. The limit varies across the country with various government organizations.
Uses: These are used for pointing, exposed face work in masonry structures, flooring and reinforced brick work.
Second class bricks
1. Little amount of cracks are permitted.
2. Higher absorption about 16–20% of its dry weight.
3. The crushing strength should not be less than 7.0 N/mm2.
Uses: These are used for all the hidden type of brick masonry.
Third class bricks
They are less burnt and light-colored produces dull sound while hitting with each other.
Uses: They are used for temporary structure due to less strength.
Fourth class bricks
Poor burned and deformed shapes and sizes and are fragile by nature.
Uses: The ballast of such bricks is used for foundation and floors in lime concrete and road metal.
On the basis of use
Common brick
It is usually performed without reference to the special purpose unit of economic production. The strength and durability, and appearance is a result of where the load is going to be used for baking and walls.
Facing bricks
They are made for architectural view only.
Engineering bricks
They are strong, impermeable, smooth, table moulded, hard and conform to defined limits of absorption and strength. These are used for all load bearing structures.
On basis of finish
Sand-faced brick
It has sand texture surface manufactured by sprinkling sand on the inner surfaces of the mould.
Rustic brick
It has mechanically textured finish, varying in pattern.
On basis of manufactured
Hand-made bricks
These bricks are hand moulded.
Machine made
Depending upon mechanical arrangement, bricks are known as wire-cut bricks—bricks cut from clay extruded in a column and cut off into brick sizes by wires; pressed- bricks—when bricks are manufactured from stiff plastic or semi-dry clay and pressed into moulds; moulded bricks—when bricks are moulded by machines imitating hand mixing.
On basis of burning
Pale bricks
They are underburnt bricks obtained from outer portion of the kiln.
Body brick
They are well burnt bricks occupying central portion of the kiln.
Arch brick
They are overburnt also known as clinker bricks obtained from inner portion of the kiln.
On basis of types
Solid
Small holes not exceeding 25 per cent of the volume of the brick are permitted; alternatively, frogs not exceeding 20 per cent of the total volume are permitted.
Perforated
Small holes may exceed 25 per cent of the total volume of the brick.
Hollow
The total of holes, which need not be small, may exceed 25 per cent of the volume of the brick.
Cellular
Holes closed at one end exceed 20 per cent of the volume.
Classification of bricks
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