Friday, May 25, 2018

BRICK


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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