Clay bricks are classified as first class, second
class, third class and fourth class based on their physical and mechanical
properties.
First
Class Bricks
·
These are thoroughly burnt and are of deep
red, cherry or copper colour.
·
The surface should be smooth and
rectangular, with parallel, sharp and straight edges and square corners.
·
These should be free from flaws, cracks and
stones.
·
These should have uniform texture.
·
No impression should be left on the brick
when a scratch is made by a finger nail.
·
The fractured surface of the brick should
not show lumps of lime.
·
A metallic or ringing sound should come
when two bricks are struck against each other.
·
Water absorption should be 12 – 15% of its
dry weight when immersed in cold water for 24 hours.
·
The crushing strength of the brick should
not be less than 10 N/mm2. This limit varies with different
Government organizations around the country.
Uses:
First class bricks are recommended for pointing, exposed face work in masonry
structures, flooring and reinforced brick work.
Second
class bricks are supposed to have the same requirements
as the first class ones except that
1.
Small cracks and distortions are permitted.
2.
A little higher water absorption of about
16 – 20% of its dry weight is allowed.
3.
The crushing strength should not be less
than 7.0 N/mm2.
Uses:
Second class bricks are recommended for all important or unimportant hidden
masonry works and centering of reinforced brick and reinforced cement concrete
(RCC) structures.
Third
class bricks are under-burnt. They are soft and
light-coloured producing a dull sound when struck against each other. Water
absorption is about 25 per cent of dry weight.
Uses
:
It is used for building temporary structures.
Fourth
Class Bricks are overburnt and badly distorted in shape
and size and are brittle in nature.
Uses:
The ballast of such bricks is used for foundation and floors in lime concrete
and road metal.
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