Chittagong University
of Engineering &
Technology
Department of Water
Resources Engineering
CE-281
Engineering Materials
Sumaya Sadia Toha
Lecturer
Department of Civil Engineering
Textbook
Syllabus
Definition
A Brick is an artificial kind of stone
made of clay whose chief characteristics
are plasticity when wet & stone like
hardness after being heated to high
temperature.
BRICKS
 It is a regular sized rectangular unit
 Used for most of the building works
 Used as substitute for stone, where
stone is not available
Uses of Bricks
Construction of walls of any size
Construction of floors
Construction of arches & cornices
Making khoa (broken bricks of required size) to
use as an aggregate in concrete
Manufacture of surki (powdered bricks) to be used
in lime plaster & lime concrete.
Ingredients of Good Brick Earth
A good brick earth mainly consists of Silica (Sand) and
Alumina (Clay)
Ingredients of Good
Brick Earth
• Alumina (Clay)(Aluminum Oxide)
• Silica (Sand)
• Lime
• Iron Oxide
• Magnesia(Magnesium Oxide)
• Alkalies & Organic Matter
Ingredients of Good Brick Earth
The ingredients are mixed in such a
proportion that
The resulting mass
with water is a plastic
mass
Can be easily moulded
and dried
without undergoing shrinkage,
cracking or warping
Ingredients of Good Brick Earth
Silica (Sand)
 Good brick earth should contain 50 to 60 %
Silica
 Presence of silica prevents cracking, shrinking
and warping of raw bricks
 Excess amount of silica destroys the cohesion
between particles and makes the bricks brittle
and weak
 Hence, durability of the bricks depends largely
on the proper proportion of silica & alumina in
brick earth
Ingredients of Good Brick Earth
Alumina (Clay)
 Alumina is the chief constituent of every kind of
clay
 A good brick earth should contain 20 to 30 % of
alumina
 Provides plasticity to earth, so that it can be moulded
 If bricks contain excess amount of alumina and
insufficient sand, they shrink, crack and warp on
drying and burning
Ingredients of Good Brick Earth
Lime
 Small quantity(1%) of lime in brick earth is desirable
 Slight amount of lime in a very finely powdered form acts as a
flux and causes silica to fuse slightly at kiln temperature
 Such slightly fused sand acts as a very hard cementing material
and bricks of large strength and durability are obtained
 Lime present in small proportion also prevents shrinkage of
raw bricks
 Excess amount of lime causes the brick to melt and its shape is
lost
Ingredients of Good Brick Earth
Oxide of Iron
 About 5 to 6 % is desirable in good brick earth
 It also helps silica to fuse at comparatively low
temperature like lime
 The color of bricks depends on the proportion of
iron oxide present in the brick earth
 The bricks having very small amount of iron
oxide are yellow in color
 Iron also increases the
impermeability of the bricks
durability
and
Ingredients of Good Brick Earth
Magnesia
 A small proportion(5%) of it decreases the
shrinkage and gives yellow tint to the bricks
 Excess amount of magnesia causes bricks to
decay
Ingredients of Good Brick Earth
Alkalies & Organic Matter
A small quantity of organic matter assist
burning the bricks.
Small quantity of Alkalies lower the fusion
point of clay.
Proportion of the Ingredients of Typical
Good Brick Earth
Ingredients
Percentage
Alumina
20-30 %
Silica
50-60 %
Lime & Magnesia
6-10 %
Iron Oxide
4-8%
Organic Matter
3-6 %
Harmful Ingredients of Brick Earth
Harmful Ingredients of Brick Earth
• Lime
• Pebbles of Stone & Gravel
• Iron Pyrites
• Alkalies
• Organic Matter
• Presence of Vegetation
Harmful Ingredients of Brick Earth
Lime
 Presence of lime in large amount is harmful
 Calcium Carbonate present in lumps is converted
to quick lime (CaO) after burning of bricks
 When these bricks come into contact with
moisture, quick lime slakes and causes
disruption of bricks because of its expansion
 Excess amount of lime also causes the brick to
melt, and its shape is lost
Harmful Ingredients of Brick Earth
Pebbles of Stone and Gravel
 Do not allow thorough mixing of the earth
 Bricks containing pebbles and gravels are
considered very week
 Such bricks cannot be broken at the desired
section, and they break very irregularly
Harmful Ingredients of Brick Earth
Iron Pyrites
 Presence of iron pyrites(FeS2) causes crystallization
and disintegration of bricks during burning
 It causes discoloration of bricks in the form of black
slag
Harmful Ingredients of Brick Earth
Alkalies
 Mainly salts of sodium and potassium
 Act as flux in the kiln and cause fusion, warping and
twisting of the bricks
 Alkalies present in bricks absorb moisture from the
atmosphere
 Such bricks when used for masonry work cause
deposition of white powder on the surface. Because when
drying; the salts, which have come to the surface with
moisture, get deposited
 This action is known as efflorescence, which seriously
spoils the appearance of the building
Harmful Ingredients of Brick Earth
Organic Matter
 Presence of organic matter and vegetation in
the brick earth render the bricks porous
Broad Classification of Bricks
Classification of Bricks
First Class Bricks
Second Class Bricks
Third Class Bricks
Over Burnt or Jhama Bricks
Under Burnt or Pilla bricks
First & Second Class Bats
Jhama Bats
First Class Bricks (S-grade,BDS 208:2002)
Properties
 Size of the burnt brick is exactly 9.5”x4.5”x2.75”
 The brick earth is free from small pebbles, lime
lumps, organic matter and sodium salts
 Well burnt
 Color is uniform yellow or red
 Surface is regular and sides are parallel, edges are
sharp and at right angles to each other
 Have firm, compact and uniform texture
 No sign of efflorescence
First Class Bricks (S-grade,BDS 208:2002)
Properties
 Crushing strength more than 280 kg/cm2 (mean
value) and 245 kg/cm2 (individual minimum value)
 Surface is so hard that finger nails are not able to
make any impression on its surface
 Does not absorb water more than 10 % of its own dry
weight
 Metallic ringing sound emits when two bricks are
struck against each other
 Does not break when it is dropped on a hard ground
from a height of 1 meter
First Class Bricks (S-grade,BDS 208:2002)
Uses
 Used in all works of long durability, say
100 years
 Used for buildings that expose to
corrosive environment
 Used as coarse aggregate of concrete
Second Class Bricks (A-grade,BDS 208:2002)
Properties
 Well burnt or slightly over burnt
 Color is uniform yellow or red
 Generally regular and uniform shape, size and
color
 Uniform texture
 No appreciable sign of efflorescence
Second Class Bricks (A-grade,BDS 208:2002)
Properties
 Ringing sound emits when two bricks are struck
against each other
 Does not absorb water more than 15 % of its own dry
weight after immersion of 24 hours in cold water
 Crushing strength more than 175 kg/cm2 (mean
value) and 154 kg/cm2 (individual minimum value)
 No finger nail impression
Second Class Bricks (A-grade,BDS 208:2002)
Uses
 Used in less important structures
 Used for general purposes
Third Class Bricks (B-grade,BDS 208:2002)
Properties
 Generally under burnt
 Soft and light red colored
 Size and shape are not regular
 Intensive efflorescence
 Texture is not uniform
 Emit a dull sound when struck against each
other
Third Class Bricks (B-grade,BDS 208:2002)
Properties
 Does not absorb water more than 20 % of its
own dry weight after immersion of 24 hours
in cold water
 Crushing strength more than 140 kg/cm2
(mean value) and 105 kg/cm2 (individual
minimum value)
 Leave finger nail impression
Third Class Bricks (B-grade,BDS 208:2002)
Uses
 Not used for important and permanent
works
 Mostly used for temporary works
Over Burnt or Jhama Bricks
Properties
 Over burnt
 Shape vitrified and distorted
Uses
 Can not be used in construction works
 Used for making aggregate for lime concrete for
foundation
 As a road material
Under Burnt or Pilla Bricks
Properties
 Half burnt
 Yellow color
 Low strength
Uses
 Crushed to powder form and used as surkhi
Manufacture of Bricks
Manufacture of Bricks
Preparation of Clay
Tempering of the Clay
Manufacture of
Bricks
Moulding of Bricks
Drying of Bricks
Burning of Bricks
Manufacture of Bricks
Preparation of Clay or Earth
 Preparation of clay involves operations like removing the
top loose earth, then digging, cleaning, weathering and
blending of the earth
 After removing the top unsuitable soil, the clay is dug
either by manual labor or by power excavators
 Dug out clay is spread out on the leveled ground and all
the pebbles, gravel, kankar, vegetable matter etc. are
removed from the clay
Manufacture of Bricks
Preparation of Clay or Earth
 The clay is left exposed to atmosphere for softening, known as weathering
of clay.
 This process has an important effect on the plasticity & strength of the
clays.
 The clay should be kept moist during the period it is weathered.
 Digging the earth before rains is advantageous as full monsoon can be
utilized for weathering
 After weathering, the earth is chemically analyzed and if there is any
deficiency of any ingredient, it is mixed with the earth
 The quality of brick clay is to be improved (if there is any deficit of
important constituent ingredients) by adding sand, lime, alumina, magnesia
etc.. This process is known blending.
 Now preparation of clay is completed
Manufacture of Bricks
Tempering of Clay
The clay is then cut, slashed & well worked with spade & is
trodden which makes it soft. This process is known as tempering.
 Tempering of clay involves breaking up of the prepared clay,
watering and kneading till the earth becomes a homogeneous
mass having uniform consistency. So that it may posses the
required plasticity for molding .
 Water is added to clay in required quantity and the whole mass
is kneaded under the feet of men or cattle
 Where good bricks are required to be manufactured on a large
scale, tempering of clay is usually done by pug-mill
Tempering of Clay
Tempering of Clay
Tempering of Clay
Manufacture of Bricks
Moulding of Bricks
 After tempering of clay, bricks should be moulded as soon as possible;
otherwise pugged clay may become stiff and moulding of bricks may
become difficult
 The bricks can be moulded by
 Hand moulding
 Machine moulding
 Moulds are rectangular boxes. They may be made of steel or timber.
 The internal dimensions of the mold are about 1/10 larger than the size of
the burnt bricks to allow for shrinkage on burning.
 Generally, identification marks (Frogs & impression) are left on the face of
the brick during the process of molding to indicate the name of the
manufacturer of bricks.
Hand Moulding
Hand Moulding
Manufacture of
Bricks
Drying of Bricks
Wet bricks have to be dried before they are fed
for burning in the kilns. The objectives of drying
the bricks are
To remove as much of moisture from the
bricks as possible, so as to save time and fuel
during the burning
To avoid the chances of cracking and distortion
of bricks during the burning
To increase the mechanical strength of the
bricks, so that they can be handled and stocked
without any damage to the bricks
Brick drying generally takes 5 to 12 days
depending upon the local climate conditions.
Drying of Bricks
Manufacture of Bricks
Burning of Bricks
 Burning of bricks is a very important operation in the
manufacturing of bricks
 It imparts strength and hardness to the bricks and makes
them dense and durable
 When temperature of bricks reaches at 650°C, while
burning, water of crystallization is removed
 At that temperature , the organic matter present in the bricks
is oxidized & disappears.
 At about 1149° C, the two main constituents of brick, silica
and alumina, combine with each other and bricks become
dense and strong
 Bricks are burnt either in clamps or in kilns
Kilns
The kiln is a system, designed more scientifically,
to burn the bricks in very large numbers
Type of Kilns
Intermittent kiln
Continuous kiln
Kilns
Intermittent Kiln
 Operation of burning the bricks is not continuous
 The kiln is loaded, then fired, then allowed to cool
and lastly unloaded
Loading
Start of Cycle
Firing
End of One
Cycle
Cooling
Unloading
Intermittent Kilns
Kilns
Disadvantages of Intermittent Kiln
 Supply of bricks is intermittent
 Quality of burnt bricks is not uniform. Bricks near
bottom are over burnt and those near top are
under burnt
 There is wastage of fuel as kiln is to be cooled
down every time after burning
Kilns
Continuous Kiln
 Continuous in operation and ensures continuous supply of
burnt bricks
 All operations like loading, firing, cooling and unloading
are carried out simultaneously in these kilns
Bull’s Trench Kiln
Mostly Used
Continuous Kiln
Hoffman’s Kiln
Tunnel Kiln
Hoffman’s Kiln
 This kiln is circular in plan
 The chimney is placed at the centre and twelve chambers are arranged around
the chimney forming a circular ring
 Each chamber has a door in the external wall which is used for loading and
unloading of bricks
 All the chambers have communicating doors in the walls separating each other
and all the chambers have a connection with chimney with radial flues
 The kiln has permanent roof, but fuel holes are provided to drop the fuel in the
kiln from top
 In this kiln, all the chambers are subjected to loading, drying and pre-heating,
burning, cooling and unloading operations successively and all these operations
remain going on all the time simultaneously
Brick Burning
Hoffman’s Kiln
Hoffman’s Kiln
All the twelve chambers of the kiln may be
functioning as follows
Chamber No.
Operation Involved
1
2, 3, 4, 5
6, 7
8, 9, 10, 11
12
Loading
Drying & Pre-heating
Burning
Cooling
Unloading
Hoffman’s Kiln
The circulation of flue gas with this arrangement
 Cool air enters the kiln through open doors of chambers 1
and 12
 This cool air passes through chambers 11, 10, 9, and 8 and
in course of time gets heated, while performing cooling of
the hot-burnt bricks in these chambers
 Now this heated air or gas enter the burning chambers 7
and 6, where it performs the burning of bricks. Fuel is
dropped in these chambers from the top
 After performing burning of bricks, hot gas is led to
chambers 5, 4, 3 and 2 where they perform drying and preheating of freshly loaded bricks
Hoffman’s Kiln
The circulation of flue gas with this arrangement
 The communicating door of chamber 2 is closed and
cooled gas is led to chimney through the radial flue of this
chamber
 Care should be taken that all radial flues except of chamber
2 remain closed and all communicating doors except in the
wall between chambers 1 and 2 remain open for this
particular arrangement. Outer loading and unloading doors
remain closed except for the two chambers, which are
being loaded and unloaded
Hoffman’s Kiln
After the burning of bricks of chamber 7 and 6, the
pattern of circulation will be as follows
Chamber No.
Operation Involved
12
Loading
1, 2, 3, 4
Drying & Pre-heating
5, 6
Burning
7, 8, 9, 10
Cooling
11
Unloading
Hoffman’s Kiln
Advantages
 There is perfect control on the heat
 Supply of bricks is continuous and regular
 Pre-heating of the bricks by hot gases before they
escape into the atmosphere, considerably reduce
the consumption of the fuel
 Preheating of un-burnt bricks
 Bricks are burnt evenly and thus bricks of good
quality are produced
 Percentage of first class brick is the highest
Hoffman’s Kiln
Disadvantages
 Initial cost of construction is high
 This kiln requires regular demand of the bricks
which may not be possible
Desirable Characteristics of Good
Bricks
 The color of good brick should be uniform. It may be deep
red or yellow
 Bricks should be uniform in shape with all its edges sharp,
straight and at right angles to each other
 Size of the bricks should be standard (24cm x 11.5cm x
7cm) as prescribed by Bangladesh Standards (BDS, 2002)
 The bricks should have fine, dense, compact and uniform
texture
 First class bricks should not absorb water more than 10 % of
its own dry weight after immersion of 24 hours in cold
water
Desirable Characteristics of Good
Bricks
 Crushing strength more than 280 kg/cm2 (mean value) and 245
kg/cm2 (individual minimum value) (BDS, 2002)
 The bricks should be so hard that fingernails should not be able to
make any impression on its surface when scratched
 Two bricks when struck against each other should emit metallic
sound
 Bricks should be soundproof and of low thermal conductivity
 Bricks should not break when dropped flat on a hard ground from
a height of 1 meter (~3 ft).
Tests for Bricks
 Absorption capacity Test
 Crushing Strength Test
 Unit weight test
 Shape and Size Test
 Soundness Test
 Test for Presence of Soluble Salts (Salinity Test)
Coloring of Bricks
Factors Affecting the Color
Amount
Degree
of air
Chemical Nature
of
Burning Type of
admitted
composit of sand
dryness
temperat fuel used
to the
ion of
used
achieved
ure of
during
kiln
the brick during
before
bricks
burning
during
earth
molding
burning
burning
The color attained by any of the above causes is
known as the natural color of the brick
Coloring of Bricks
 Bricks can be colored artificially also
 By dipping (immersing in coloring mixture)
 By mixing appropriate coloring material
during preparation of brick earth/clay
Fire Bricks or Refractory Bricks
 These bricks are manufactured from specially
designed earth, so that after burning, they can
withstand very high temperatures without
affecting its shape, size and strength
 They are used for lining of chimneys, furnaces
etc., where usual temperatures are expected to be
very high
Special Bricks
Purpose made bricks
Fire bricks
Ordinary Fire bricks
Silica Bricks
Acidic Bricks
Basic Bricks
Neutral Bricks
Chromite Bricks
High Alumina Bricks
Calcium Silicate Bricks
Special Bricks
Bullnose bricks
Channel bricks
Coping Bricks
Cownose Bricks
Curved Sector Bricks
Hollow Bricks
Paving Bricks
Perforated bricks
Fly-Ash bricks