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