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BRICKS
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Brick is nothing but baked clay- an artificial stone made by forming clay into rectangular
blocks which are hardened by burning/ sun-drying in warm countries.
Used for most of the building works.
Used as substitute for stone, where stone is not available.
Ingredients:
1. Silica (SiO2)
: 55%
2. Alumina (Al203
: 30%
3. Iron oxide (Fe203) : 8%
4. Magnesia (MgO) : 5%
5. Lime
: 1%
6. Organic matter
: 1%
Functions of Chief ingredients:
1. Silica
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Good brick contain 50-60%
Prevents shrinkage, cracking & warping of bricks, thereby imparts shape to it.
Excess amount in bricks destroys cohesion between particles and makes bricks brittle and
weak.
2. Alumina:
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Brick contains 20-30%.
Main constituent of clay.
Provides plasticity to clay so that it can be moulded.
If contains excess amount, bricks shrink, crack and warp on drying and burning.
3. Iron oxide:
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Should contain a small quantity.
Acts a s a flux like lime, thus helps silica to fuse at low temperature.
Imparts red color to brocks on burning.
Zasiah Tafheem/ Assistant Professor/ Department of Civil Engg./ AUST / CE201 / Engineering Materials/ Brick
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4. Magnesia:
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A small proportion of it decreases the shrinkage & gives yellow tint to the bricks.
Excess amount causes bricks to decay.
5. Lime:
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Bricks should contain a little finely powdered lime.
It enables silica to melt at furnace heat & binds the particles of brick together resulting in
strong & durable bricks.
Excess lime makes brick vitrified, causes brick to melt and thus its shape is lost.
Harmful Ingredients:
Alkalies:
▪ Mainly salts of Na & K.
▪ Acts as a flux in the kiln and causes fusion, warping and twisting of bricks.
▪ Alkalies absorb moisture from atmosphere and causes dampness & efflorescence.
[Efflorescence: The deposition of salts on the surface of clay/ceramic materials is called
efflorescence. It creates a thin white film. It is resulted from migration and evaporation of
aqueous saline solution. Efflorescence is basically an aesthetic problem. Raw materials,
building materials, subsoil water can be the source of soluble salts. It may damage plaster.]
Pebbles, stones & Gravels:
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Their presence does not allow thorough & uniform mixing of earth/clay thus makes
bricks weaker, non-uniform.
Iron pyrites (FeS):
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Causes crystallization & disintegration of bricks during burning.
Discolors bricks in the form of black slag.
Organic matter:
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Makes bricks porous resulting in low density, porous and weaker bricks.
Zasiah Tafheem/ Assistant Professor/ Department of Civil Engg./ AUST / CE201 / Engineering Materials/ Brick
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Characteristics of Good Bricks:
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Uniform color (deep red/cherry)
Uniform shape (edges sharp, straight & at right angles with other edge)
Size; standard (i.e. 9.5 ×4.5× 2.75 in. by PWD)
Texture and compactness (fine, dense & compact)
Should not absorb more than about 1/5 of their own weight of water when immersed in
water for 24 hours (15-20% of dry weight)
% of soluble salts (Sulphates of calcium, magnesium, sodium and potassium) should not
exceed 2.5%.
Hardness (no finger nail impression on brick surface)
Should be sound and compact (emits metallic sound or ringing sound)
Free from any kind of non-homogeneity because of gravels, stones etc.
Should be free from cracks and other flaws.
Sound proof & low thermal conductivity
Should be incombustible.
Laboratory Tests for Bricks:
a. Absorption Capacity test (See Page 361-363 from the book of Dr. Latiffe)
b. Crushing Strength test (See Page 361-363 from the book of Dr. Latiffe)
c. Soluble salt test (See Page 95-96 from CE 202 Lab Manual)
Field tests for Brick:
a) Arrange two bricks so as to form a 'T' and allow free fall from a height of 1.2m (4ft) to
1.5m (5 ft) on to level ground. If the brick pair resists breakage, the bricks are good.
b) If it is not possible to impart a finger nail scratch on to the surface of a brick, it is a good
brick, sufficiently hard and compact.
c) If hammered a brick with another of similar kind or a hammer and if a clear metallic or
ringing sound emits, the brick is good.
Zasiah Tafheem/ Assistant Professor/ Department of Civil Engg./ AUST / CE201 / Engineering Materials/ Brick
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Broad classification of Bricks:
1) 1st class Brick
▪ Standard sized, uniform yellow or red colored.
▪ Well burnt, regular shaped, uniform textured.
▪ No efflorescence, no pebbles, gravels or organic matter
▪ Absorption capacity < 20%, Crushing strength > 1500 psi
▪ Emits metallic sound, no finger nail impression.
2) 2nd class Brick
▪ Standard sized, uniform yellow or red colored.
▪ Well burnt (slightly over burnt is expectable), regular shaped.
▪ Efflorescence is not appreciable.
▪ No limestone.
▪ 20 <Absorption capacity < 22%, Crushing strength > 1000 psi
▪ Emits metallic sound, no finger nail impression.
3) 3rd class Brick
▪ Soft & light red colored; Shape and size not regular.
▪ Under burnt (slightly over burnt is acceptable).
▪ Extensive efflorescence, non-uniform texture.
▪ Absorption capacity >22%, Crushing strength <1000 psi
▪ Emits dull or blunt sound.
▪ Left finger nail scratch mark
4) Over-burnt or Jhama Brick
▪ Vitrified.
▪ Shape is distorted.
▪ High absorption capacity.
▪ Strength may be high or equivalent of 1st class brick.
5) Under-burnt or Pilla Brick
▪ Half-burnt used as surki.
▪ Yellow-colored.
▪ Low strength.
Notes:
✓ Under-burnt brick becomes yellow for the presence of magnesia.
✓ Surki has high absorption capacity. It is used instead of sand. Burnt surki is used as
JALSAD.
Zasiah Tafheem/ Assistant Professor/ Department of Civil Engg./ AUST / CE201 / Engineering Materials/ Brick
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✓ Half brick is called bats. Bats are also classified in 1st, 2nd & 3rd class bricks.
Zasiah Tafheem/ Assistant Professor/ Department of Civil Engg./ AUST / CE201 / Engineering Materials/ Brick