BRICK
Introduction
•
Bricks are
rectangular block made of fired or sun-dried clay used in buildings
•
Brick earth is
derived by disintegration of igneous rocks
•
Size of mould for
bricks should be slightly larger than the specified size of bricks because
brick shrinks
•
Brick after moulding
should be dried in air for 3 to 8 days but not in sun
•
Perforated bricks
have compressive strength of 7 N/mm2
•
Paving bricks
have compressive strength of 40 N/mm2
•
As per IS code
size of brick should be 190mm x 90mm x 90mm
•
Specific gravity
of brick is about 2
•
Number of bricks
required for 1 cubic meter of brick masonry is 550
•
Number of machine
made bricks per cubic meter is 530
•
Number of handmade
bricks per cubic meter is 560
•
Process of mixing
clay, water and other ingredients to make brick is called kneading
•
Raised ground for
drying bricks is called hacks
•
Brick is brunt in
kiln for 24 hours at 10000C to12000C
Stone vs
brick
Stone
|
Brick
|
Heavier than brick
|
Lighter than stone
|
Hard and Tough
|
Hard and sound
|
Absorbs more heat
|
Absorbs less heat than stone
|
High durability
|
Durability is less than
that of stone
|
Water absorption is less
than 5%
|
Water absorption is more
than that of stone
|
Constituent
of brick
•
Alumina or clay =
20-30 % by weight
•
Silica or clay =
35-50% by weight
•
Silt = 20-25% by
weight
•
The total content
of clay and silt may preferably be not less than 50% by weight
•
Iron oxide,
Magnesia, Lime, sodium potash, etc. should by 1-2% by weight
•
The lime should
be in finely divided form
•
The total water-soluble
material should not be more than 1% by weight
Function of
ingredients of brick
Alumina
•
Uses
•
Principal
constituent of every kind of brick earth
•
Provides
plasticity and makes brick hard
•
Absorbs water
•
Excess of alumina
causes
•
Cracks in brick
on burning
•
Warp on drying
•
Warping means
becoming bent or twisted out of shape
Silica
•
Uses
•
Retain shape of
brick
•
Imparts
durability
•
Prevents
shrinkage
•
Prevents warping
•
Provide resistant
to heat
•
Excess of Silica
•
Makes brick
brittle and weak
Lime
•
Uses
•
Reduce shrinkage
•
Act as flux:
Helps silica to melt at lower temperature and binds the particles of bricks
together
•
Excess of Lime
cause
•
Melting of brick
•
Distortion of
shape/Disintegrating the brick
Alkalis
•
Excess of alkalis
•
Efflorescence
•
Efflorescence is
crystalline deposit of salt on the surface of brick
Iron oxide
•
Iron oxide
shouldn’t be in form of Iron Pyrite
•
Uses of Iron
Oxide in Brick
•
Imparts red color
to the brick
•
Excess of Iron
Oxide
•
Makes brick dark
blue
Magnesia
•
Uses
•
Causes clay to
soften at slower rate
•
Reduces warping
•
Excess of
Magnesia
•
Affects color and
make it yellow
•
Decay of bricks
Harmful
ingredients in brick earth
•
Lime in Lump: Lime
should be in finely divided state otherwise the lump on burning will change to
quick lime and disintegrate the brick on absorbing the moisture
•
Alkalis: Alkalis
cause brick to fuse, twist and warp on burning. When moisture dries up,
efflorescence is caused by depositing salt on surface of brick
•
Pebbles of stone and gravel: They
impair the uniformity of brick and do not permit clay to be thoroughly mixed.
•
Iron pyrites:
Iron pyrites decompose and oxidize in the brick and cause the brick to split.
•
Vegetation and organic matter: They
make brick porous.
Defects of
brick
•
Over burning
•
Soften mass is
produced
•
Brick lose their
shape
•
Under burning
•
High water
absorption
•
Less compressive
strength
•
Bloating
•
Spongy swollen
mass over the surface of burned bricks are formed
•
It is due to the
presence of excess carbonaceous matter and Sulphur in brick-clay
•
Black core
•
This is cause if
brick contains bituminous matter or carbon
•
Chuff
•
It is deformation
or crack on brick surface
•
It is caused when
cool (rain) water falls on hot bricks
•
Cracks and checks
•
It is caused due
to lumps of lime or excess or water
•
Lamination
•
It is caused by
entrapped air in voids of clay
•
Spots
•
It is in case of
presence of iron sulphide in clay soil
•
It doesn’t affect
the strength of brick
•
It makes brick
unsuitable for external face brick
Classification
of brick
•
Sun dried
•
These bricks are
dried with the help of heat received from sun
•
They are used in
construction of temporary and cheap structure
•
They shouldn’t be
used at places exposed to heavy rainfall
•
Burnt bricks
•
They are burnt in
a clamp or kiln after moulding and drying
•
They are hard,
strong and durable
•
They are generally
used in permanent structure
Burnt bricks
classification
•
Burnt bricks are
further classified as
•
First class brick
•
Second class
brick
•
Third class brick
First class
bricks
•
They are
table-moulded and burnt in kilns
•
Water absorption
after 24 hours of it own weight
shouldn’t be more than 20%
•
Minimum crushing
strength is 10.5 N/mm2
•
They are well
burnt and regular in shape
•
When two bricks
are struck, metallic ringing sound is produced
•
No mark can be
produced by finger nails
•
Edges are sharp
and well defined
•
Hard and sound
and have uniform color
•
Smooth, clean and
free from cracks
Uses of
first class brick
•
In Reinforced
brick works
•
As ballast for
Reinforced concrete works
•
Shaped bricks are
used in carvings, arches and copings
Second class
bricks
•
They are ground
moulded and are burnt in kilns
•
Water absorption
after 24 hours of it own weight
shouldn’t be more than 22%
•
Minimum crushing
strength is 7 N/mm2
•
They are well
burnt but irregular in shape and size
•
They have rough
surface
•
Edges are neither
straight nor well defined
•
They are not free
from lumps and cracks
•
They don’t have
uniform color
•
They produce
ringing sound when struck with one another
Uses of
second class brick
•
It is used in
unimportant situation
•
It is used for internal walls where the bricks
are generally hidden from view
Third class
brick
•
They are ground
moulded and burnt in clamps
•
They are under
brunt and are not uniform in shape and size
•
They are also
called pilla bricks
•
They have light yellowish
color
•
They are soft
•
A dull sound is
emitted when two bricks are struck
•
Their edges are
irregular and surface are quite rough
•
They are
associated with cracks and flaws
Uses of
third class brick
•
They are used in
inferior and temporary buildings
Some Brick
class summary
Class of brick
|
Water absorption after 24hrs of its own dry weight
|
Minimum Crushing strength (N/mm2)
|
Burnt quality
|
First class brick
|
Not greater than 20%
|
10.5
|
Well
|
Second class brick
|
Not greater than 22%
|
7
|
Well
|
Third class brick
|
Not greater than 25%
|
under
|
Class of brick
|
Moulding
|
Burnt in
|
First class brick
|
Table
|
Kilns
|
Second class brick
|
Ground
|
Kilns
|
Third class brick
|
Ground
|
clamps
|
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