Bricks

Civil Engineering Materials, Er. Jayant Chaudhary
pg. 1
Table of Contents
UNIT-3 : BRICKS..................................................................................................................................2
3.1 Introduction.................................................................................................................................2
3.2 Classification of Bricks ................................................................................................................4
3.3 Constituent/Composition of Good Bricks.....................................................................................5
3.4 Harmful Ingredients in Brick Earth:..............................................................................................6
3.5 Properties of Good Bricks: ..........................................................................................................7
3.6 Manufacturing of Bricks:..............................................................................................................8
3.2 Other Classification of Bricks ....................................................................................................19
3.7 Test on Bricks...........................................................................................................................24

pg. 2
UNIT-3 : BRICKS
3.1 Introduction
➢ In ancient times, bricks were typically made using a mixture of mud and straw. The mud, which
was the main component of the brick, was dug from the ground and mixed with water.
➢ Straw was then added to the mixture to act as a binding agent and to provide structure to the
brick.The mud and straw were mixed together until they formed a consistent mixture, which was
then shaped into bricks using molds. The bricks were then left to dry in the sun.
➢ Some ancient civilizations, such as the Mesopotamians, developed the technology to fire bricks
in kilns. This increased the strength and durability of the bricks by hardening the surface, and
also helped to remove the moisture.
➢ In ancient China, bricks were made from a mixture of clay, sand and lime. The clay was mixed
with water and sand to form a paste, which was then shaped into bricks and dried in the sun
before being fired in a kiln.
➢ In ancient Rome, bricks were made of clay mixed with volcanic ash. The ash helped to strengthen
the bricks and made them more durable.
➢ In ancient Indus Valley Civilization, Bricks were made of mud mixed with chaff and then shaped
and dried in the sun.
Overall, the exact ingredients used to make bricks in ancient times varied depending on the
location and the resources that were available.
Clay and its classification:
• Clay is the most important raw material used for making bricks.
• It is an earthen mineral mass or fragmentary rock capable of mixing with water and forming
a plastic viscous mass which has a property of retaining its shape when moulded and dried.
• When such masses are heated to redness, they acquire hardness and strength. This is a
result of micro-structural changes in clay and as such is a chemical property.
• Purest clays consist mainly of kaolinite (2SiO2.Al2O3.2H2O) with small quantities of
minerals such as quartz, mica, felspar, calcite, magnesite, etc.
• By their origin, clays are subdivided as residual and transported clays.
➢ Residual clays, known as Kaolin or China clay, are formed from the decay of underlying
rocks and are used for making pottery.
➢ The transported or sedimentary clays result from the action of weathering agencies.
These are more disperse, contain impurities, and free from large particles of mother rocks.
• On the basis of resistance to high temperatures (more than 1580°C), clays are classified
as refractory, high melting and low melting clays.

pg. 3
➢ The refractory clays are highly disperse and very plastic. These have high
content of alumina and low content of impurities, such as Fe2O3, tending to lower
the refractoriness. Refractory clays are used in a variety of applications, such
as making firebricks and blocks, insulating bricks, saggers, refractory mortars
and mixes, monolithic and castable materials, ramming and air gun mixes, and
other products.
➢ High melting clays have high refractoriness (1350-1580°C) and contain small amount of
impurities such as quartz, felspar, mica, calcium carbonate and magnesium carbonate.
These are used for manufacturing facing bricks, floor tiles, sewer pipes, etc.
➢ Low melting clays have refractoriness less than 1350°C and have varying compositions.
These are used to manufacture bricks, blocks, tiles, etc.
• Admixtures are added to clay to improve its properties, if desired.
• Highly plastic clays which require mixing water up to 28 per cent, give high drying and burning
shrinkage, call for addition of lean admixtures or non-plastic substances such as quartz sand,
chamottee (Chamotte is calcined clay containing a high proportion of alumina), ash, etc.
• Acid resistance items and facing tiles are manufactured from clay by addition of water-glass or
alkalis.
• Burning temperature of clay items can be reduced by blending clay with fluxes such as
felspar, iron bearing ores, etc.
• Plasticity of moulding mass may be increased by adding surfactants such as sulphite-sodium
vinasse (0.1-0.3%).
Clay possesses following properties:
• Clay possesses plasticity when moist.
• Clay possesses rigidity when dried.
• Clay possesses strength and hardness when fired.
Bricks :
• The artificial material of construction in form of clay bricks of uniform size of shape are known
as bricks.
• Weight = 2 to 3 kg
• Density = 1800kg/m3
As per NBC (Nepal Building Code)
• Bricks : The bricks shall be of a standard rectangular shape, burnt red, hand-formed or
machine-made, and of crushing strength not less than 3.5 N/mm².
• The higher the density and the strength, the better they will be.
• The standard brick size of 240 x 115x 57mm with 10 mm thick horizontal and vertical mortar
joints is preferable. Tolerances of -10 mm on length, -5 mm on width and ±3 mm (230 x 110x
54N61) on thickness shall be acceptable for the purpose of thick walls.

pg. 4
• Wall Thickness : A minimum thickness of one half-brick and a maximum thickness of one brick
shall be used.
• Mortar : Cement-sand mixes of 1:6 and 1:4 shall be adopted for one-brick and a halfbrick thick
walls, respectively. The addition to the mortars of small quantities of freshly hydrated lime in a
ratio of ¼ to ½ of the cement will greatly increase their plasticity without reducing their strength.
Hence, the addition of lime within these limits is encouraged.
• Plaster : All plasters should have a cement-sand mix not leaner than 1:6. They shall have a
minimum 28 days cube crushing strength of 3 N/mm².
Important role/uses of bricks:
Bricks are a versatile building material that can be used in a variety of ways in civil engineering projects.
• They can be used to construct walls, foundations, and other structural elements
• They are commonly used for building houses, buildings, and other structures, and can be used
in both load-bearing and non-load-bearing walls
• Bricks are strong and durable, making them ideal for use in load-bearing walls and other
structural elements.
• Construction of arches, cornices, brick retaining wall, etc.
• Making Khoa (Broken bricks of required size) to use as an aggregate in concrete.
• Manufacture of surkhi (powdered bricks) to be used in lime plaster and lime concrete.
• They are fire-resistant, making them ideal for use in buildings that need to be protected from fire.
• Bricks are relatively inexpensive and easy to work with, making them an attractive option for
many civil engineering projects.
• They can be produced in large quantities and can be transported easily.
• They are easy to lay and can be used with a variety of different mortar types.
• Bricks also have good insulation and sound insulation properties which helps to reduce energy
consumption and noise in buildings.
• They have a relatively long life-span, which means they do not need to be replaced as frequently
as other building materials, making them more sustainable in the long-term.
3.2 Classification of Bricks
1. First Class Bricks
• It is table/machine moulded and burned in kilns (well burnt).
• Deep red, cherry colour
• It should have uniform appearance and texture.
• Smooth, rectangular, parallel and sharp edges.
• Should not break when dropped from a height of 1 to 2m.
• Metallic and clinging sound when struck with each other.
• Water absorption = 12-15% of its dry weight.
• Its absorption shall not exceed 20% when immersed in water for 24 hours.
• Crushing strength >= 10N/mm2
• The average crushing strength of first class bricks shall not be less than 17 N/mm².
• These bricks are more durable and have more strength.
• Uses : - First class bricks are recommended for pointing, exposed face work in masonry
structures, flooring and reinforced brick work.

pg. 5
2. Second Class Bricks
• It is ground moulded and burned in kilns (well burnt).
• Rectangular but slight irregularity is permitted.
• Surface may be slightly uneven.
• Metallic and clinging sound when struck with each other.
• Its absorption shall not exceed 22% when immersed in water for 24 hours.
• Uses : - Unimportant hidden masonry work and RCC work.
3. Third Class Bricks
• It is ground moulded and burned in clamps.
• It may be poorly burnt, overburnt or under burnt.
• Soft and reddish.
• Rough, irregular and distorted edges.
• Produce dull sound when struck with each other.
(3.5 to 7 N/mm2
).
• Uses: It is used for building temporary structures
4. Fourth Class Bricks (Jhama Bricks)
• These are overburnt hence dark in colour.
• Badly distorted in shape and size.
• Brittle in nature.
• Water absorption = less than 10% of its dry weight.
• The average crushing strength of Jhama Bricks shall not be less than 20 N/mm².
• It is strong having compressive strength.
• Uses : - Foundation works, road construction work, aggregates for making of concrete.
3.3 Constituent/Composition of Good Bricks
a) Silica or Sand
• Percentage - 50-60%
• Fuction - Absorbs water and provided durability.
• It gives the qualities of hardness, strength, resistance to heat, durability.
• It prevents cracking, shrinkage, warping of raw brick.
• It reduces shrinkage during burning.
• It imparts uniform shape to the bricks.
• Excess = destroys cohesion between particles and brick becomes brittle and porous, weak in
nature.
b) Alumina
• Percentage - 20-30%
• Function - provides plasticity and helps in moulding.
• Excess - causes cracking and warping on drying and burning.
• Clays having exceedingly high alumina content are likely to be very refractory.
c) Lime
• Percentage - <10%

pg. 6
• A small quantity of lime not exceeding 5 % is desirable in good brick earth.
• Function - prevents shrinkage on drying, fusion.
• Lime help to bond Silica and Alumina.
• Excess - causes brick to melt and hence, brick loses its shape.
• The lumps of lime are converted into quick lime after burning and this quick lime slakes and
expands in presence of moisture. Such an action results in splitting of bricks into pieces.
d) Iron Oxide
• This oxide acts as a flux, it lowers down the softening temperature of silica and other clay
components during firing.
• Function - improves impermeability and durability, red colour.
• It helps as lime to defuse sand.
• Excess - causes cracking and warping on drying.
• The excess of oxide of iron makes the bricks dark blue or blackish. If less, the bricks will be
yellowish in color.
e) Magnesia
• Function - imparts yellow tint and reduce shrinkage.
• Excess - causes cracking and warping on drying. Excess of magnesia leads to the decay of
bricks.
3.4 Harmful Ingredients in Brick Earth:
1. Limestone and Kankar nodules: On heating, limestone is converted into lime which on contact
with water swells and causes the brick to split and crumble into pieces. But a certain quantity of
limestone is desirable as it binds the particle of brick together & reduces shrinkage on drying.
2. Alkalies (Alkaline salts) : Alkali present in the brick earth, they lower the fusion point of clay and
cause the brick to fuse, twist and warp during burning. Alkaline salts in brick are mainly in the
form of soda or potash.When bricks come in contact with moisture, water is absorbed and the
alkalis crystallise. On drying, the moisture evaporates, leaving behind grey or white powder
deposits on the brick which spoil the appearance. This phenomenon is called efflorescence.
3. Pebbles of stone and gravel: It causes difficulty during the mixing of clay or brick earth and
produces non-homogenous mass. They do not permit the clay to be thoroughly mixed and thus
impair the uniformity of a brick, spoil the appearance of the brick. Bricks with pebbles and
gravels may crack while working.
4. Iron pyrites: If it present in earth decompose and oxidize in the brick and cause the brick to split.
5. Sulphur is usually found in clay as the sulphate of calcium, magnesium, sodium, potassium or
iron, or as iron sulphide. Generally, the proportion is small. If, however, there is carbon in the
clay and insufficient time is given during burning for proper oxidation of carbon and sulphur,
the latter will cause the formation of a spongy, swollen structure in the brick and the brick will
be decoloured by white blotches.
6. Kallar or reh: It is the sulphate of soda mixed with a little carbonate of soda and common salt.
Its presence in brick earth prevents bricks from being properly burnt. After the bricks have been

pg. 7
burnt these salts recrystallize and appear as irregular and unsightly white patches on the surface
of bricks.
7. Vegetation and organic matter: The presence of vegetation and organic matter in brick assist
in burning. But if such matter is not completely burnt, the bricks become porous. The water
absorption is increased and the strength is reduced.
3.5 Properties of Good Bricks:
1. Physical Properties:
a) Shape: Smooth, rectangular, parallel, straight and sharp edges.
b) Size: The size of the brick used in construction varies from country to country and from
place to place in the same country. The basic standard size used in Nepal is 240 x 115x
57mm with 10 mm thick horizontal and vertical mortar joints is preferable. Tolerances of -
10 mm on length, -5 mm on width and ±3 mm (230 x 110x 54N61)but in India the ideal
size of brick 19× 9× 9 cm with which mortar joint gives net dimension of 20× 10× 10 cm.
c) Colour: Uniform deep cherry red colour.
d) Density: The density of bricks or weight per unit volume depends mostly on the type of
clay used and method of brick moulding. In the case of standard bricks, density varies from
1600 kg/m3
to 1900 kg/m3
. A single brick (19× 9× 9 cm) will weigh between 3.2 to 3.5 kg.
e) Hardness - when scratched with finger nail it should not make any impression.
f) Toughness - Brick should not break when dropped from a height of 1m.
g) Soundness - metallic and clinging sound when struck with each other.
h) Water absorption : - Not more than 20% of its dry weight when it is immersed in cold water
for 24 hours.
i) Specific gravity should be greater than 1.8.
2. Mechanical Properties:
a) Compressive Strength: It is the most important property of bricks especially because
they are to be used in load bearing walls. The compressive strength of a brick depends
on the composition of clay and degree of burning. Crushing strength >= 10 Mpa.
b) Flexure Strength: Bricks are often used in situations where bending loads are likely to
develop in building. As such, bricks used in such places should possess sufficient strength
against transverse loads. Flexure strength of bricks shall not be less that 10 kg/cm2. The
best graded brick should have the flexure strength of 20 kg/cm2
.
c) Thermal Characteristics: Besides being hard and strong, an ideal brick should also
provide adequate insulation against heat, cold and noise. The heat and sound conductivity
of bricks varies greatly with their density and porosity. Very dense and heavy bricks conduct
heat and sound at greater rate. They have poor thermal and acoustic insulation qualities.

pg. 8
d) Durability: By durability of bricks it is understood the length of time for which they remain
unaltered and strong when used in construction. Experience has shown that properly
manufactured bricks are among the most durable of man-made materials of construction.
The durability of bricks depends upon absorption value, frost resistance and efflorescence.
3.6 Manufacturing of Bricks:
1. Selection of suitable type of clay: Good type of bricks cannot be made from every type of clay.
A suitable brick earth should have good compositions. Aluminum (20-30%), Silica (50-60%),
Iron Oxide (<7%), lime (5-10%) and other ingredients.
2. Additives in the manufacture of bricks such as
• Fly ash contains amorphous glassy material, mullite, haematite, magnetite, etc. and shows
a chemical composition similar to brick earths. These silicates also help towards strength
development in clay bodies on firing, when mixed in optimum proportion.
• Sandy Loam: Addition of sandy loam is often found effective in controlling the drying behaviour
of highly plastic soil.
• Basalt Stone Dust: Basalt stone occurs underneath the black cotton soil and its dust is a waste
product available in large quantity from basalt stone crushing units. The finer fraction from
basalt stone units is mixed with soil mass to modify the shaping, drying and firing behaviour
of bricks.
3. Preparation of Brick Earth.
• Unsoiling - Removal of top layer of soil of about 200mm depth.
• Digging - Clay is dug out and spread out.
• Cleaning - Screening is done to make it free from stones, pebbles, vegetable matter, etc.
• Weathering - Clay is exposed to atmosphere for softening. Water is mixed in excavated soil
and leave to few weeks. This improves the plasticity and strength.
• Blending - Clay is loosened and mixing the appropriate ingredients of brick
• are spread over it and dry vertical mixing is done.
• Tempering - Clay is added with sufficient quantity of water and mixed under pressure to make
it ready for moulding.
4. Moulding
• Process of giving required shape to plastic clay.
MOULDING
HAND MOULDING MACHINE MOULDING
GROUND
MOULDING
TABLE
MOULDIN
G
PLASTIC CLAY
MACHINE
DRY CLAY
MACHINE

pg. 9
• The moulding process during the manufacture of bricks involves shaping and cutting the
clay mixture before it is fired in a kiln. This can be done using several methods:
a) Hand moulding
b) Machine moulding
Hand moulding:
• This is the oldest method of brick moulding and is still used today in some small-scale
brickyards. The clay mixture is placed in a wooden or metal frame (called a mould) and is
shaped by hand to the desired shape and size.
• Ground Moulding:
➢ The bricks are moulded on the levelled ground.
➢ This method is adopted when a large and level land is available.
➢ To prevent the moulded bricks from sticking to the side of the mould, sand is sprinkled
on the inner sides of the mould, or the mould may be dipped in water every time before
moulding is done. The bricks so produced are respectively called sand moulded and slop
moulded bricks, the former being better since they provide sufficient rough surface
necessary for achieving a good bond between bricks and mortar.
• Table Moulding:
➢ The bricks are moulded on stock boards nailed on the moulding table .
➢ Stock boards have the projection for forming the frog.
➢ The process of filling clay in the mould is the same as ground moulding.
➢ After this, a thin board called pallet is placed over the mould. The mould containing the
brick is then smartly lifted off the stock board and inverted so that the moulded clay along
with the mould rests on the pallet.
➢ The mould is then removed and the brick is carried to the drying site.

pg. 10
Machine moulding:
• This method uses a machine that automatically shapes and cuts the clay mixture into bricks. The
machine can produce bricks in various shapes and sizes, and can also be used to create
decorative patterns and designs.
• It is cheaper in long run and gives brick of uniform quality.
• Moulding can be done by either of the following processes:
➢ Plastic method (Stiff mud method / Plastic clay machine) - for soft clay
➢ Dry-press method (Dry clay machine) - for hard clay
• Stiff mud method: - In this method, the thoroughly cleaned brick clay is mixed with only a
small quantity of water (8-12% by volume) during tempering in pug mills so that it is quite stiff
in consistency. The stiff mix is then made to pass out under pressure from a moulding
machine.
• Dry press method: - The moist, powdered clay is fed into the mould on a mechanically
operated press, where it is subjected to high pressure of 50-150 kg/cm2
and the clay in the
mould takes the shape of bricks. Such pressed bricks are more dense, smooth and uniform
than ordinary bricks. These are burnt carefully as they are likely to crack.
•
5. Drying:
Drying is done before burning for at least three reasons;
➢ It is done to make green brick strong enough to bear rough handling during stacking, etc..
in kilns for buring
➢ To allow loss of moisture from brick at slow rate otherwise disintegration may occur
➢ and to save fuel during burning stage.
• Green bricks contain about 7-30% moisture depending upon the method of manufacture.
• The drying shrinkage is dependent upon pore spaces within the clay and the mixing water.
• Drying may be achieved by two methods;
➢ Natural Drying
➢ Artificial Drying
Natural Drying
• In this method, the bricks are stacked in layers with a enough space left between the individual
bricks and also between layers for free calcination of air around each brick. The stacks are
properly protected from direct sun, rain and strong winds. It may take 4 to 10 days depending
upon the season and place of drying.
• Air Dry: 4-10 days, 2-4% moisture remained.

pg. 11
• Sun Dried: Dried directly from sunlight. Takes 25 days to dry.
Artificial drying:
• When bricks are required on large numbers and in rapid rate. It can be achieved either in specially
designed Chamber drying or Tunnel Drying
• Chamber Drying: Bricks are arranged in stacks, within specially designed drying chambers
keeping sufficient spaces for free circulation of hot air around them. Hot air under controlled
condition of temperature and humidity is made to circulate through these stacks for 2-4 days or
more.
• Tunnel Drying: Bricks are stacked on mobile cars that are made travel o rails within a specially
designed drying tunnel.The tunnel is divided into compartments and each car loaded with green
bricks is made to stay in a particular compartment for pre-fixed condition. The cars come out
from the other end of the tunnel one by one. This process may take 2-3 days for a car load of
bricks to dry to desired extent.
6. Burning:
It is very much essential to develop desired building properties such as strength,
durability, hardness and resistance to decay and disintegration in the bricks. At least three
chemical process are known to take place in the brick earth during the burning process: -
a) Dehydration :
• This is also known as water smoking stage.
• It means complete removal of water from the pores of the bricks.
• It is completed at the temperature range of 400-650°C. Bricks heated at this
temperature loose all the free water and also to a good extent the water of
crystallization from its components.
• During dehydration, (1) the water which has been retained in the pores of the
clay after drying is driven off and the clay loses its plasticity, (2) some of the
carbonaceous matter is burnt, (3) a portion of sulphur is distilled from pyrites.
(4) hydrous minerals like ferric hydroxide are dehydrated, and (5) the carbonate
minerals are more or less decarbonated.
• On the other hand, if alkali is contained in the clay or sulphur is present in large
amount in the coal, too slow heating of clay produces a scum on the surface
of the bricks.
b) Oxidation:
• It starts taking place during heating of the bricks at the above temperature range
and gets completed at the temperature range of 650-900°C. All the organic
matter in the brick earth gets oxidized.
c) Vetrification:
• It is the last reaction that takes place at temperatures ranging from 900 - 1100°C
for low melting clay and and 1100 - 1250°C for high melting clay is required to
take place in tiles. In this process, the constituents of clay that is alumina and
silica start softening in the presence of the fluxing compounds. The constituents
grain get bound firmly.
Methods of Burning:
a) Clamp or Pazawah
b) Brick Kilns

pg. 12
Clamp or Pazawah : -
• The bricks and fuel are placed in alternate layers. The amount of fuel is reduced
successively in the top layers. The fuel consist of wood, cow dung, waste paper, straw,
etc.
• A sloping ground of trapezoidal shape and slope angle of about 15 C for high melting
clay is required to take place in tiles. In this process, is prepared.
• Each brick tier consists of 4-5 layers of bricks. Some space is left between bricks for
free circulation of hot gasses. The first layer of fuel is laid upto a height of about 1m.
• After 30 per cent loading of the clamp, the fuel in the lowest layer is fired and the
remaining loading of bricks and fuel is carried out hurriedly.
• The top and sides of the clamp are plastered with mud. Then a coat of cow dung is
given, which prevents the escape of heat. It is allowed to burn for 6 to 8 weeks. After
this stage, the bricks are left in the clamp to cool for 6 to 8 weeks. Then the burnt bricks
are taken out from the clamp.
• The production of bricks is done in small scale and the process is completed in six
months. This process yields about 60 per cent first class bricks.
Advantage:
• It is easy to erect and operate.
• Bricks obtained are strong and tough.
• No skilled supervision is required.
• It is comparatively very economical.
Disadvantage:
• Non-uniformity of shape of bricks.
• A long process to produce bricks.
• No control in the firing process.
• Non uniformity in the quality of bricks.
BURNING
CLAMPS KILNS
INTERMITTENT CONTINUOUS
Up Draft Kiln
Down Draft Kiln
Bull Trench Kiln
Hoffman Kiln
Tunnel Kiln

pg. 13
Kilns: -
• Permanent structures for burning bricks are called kilns. Kilns may be intermittent or
continuous kiln depending upon their priciple of construction.
Intermittent kiln:
• After loading the kiln, it is fired, cooled and unloaded and then the next loading is done.
• Since the walls and sides get cooled during reloading and are to be heated again during
next firing, there is wastage of fuel.
Intermittent Updraft kiln:
• Updraft kilns are those in which the flame is introduced into the bottom of the kiln, at or below
floor level, and exhausted out the top.
• Updraft kilns consist of three basic components: the firebox, the damper, and the stack area.
• The firebox is where the flame enters. The damper is at the top of the kiln and controls the
exhaust . The stack area is where the pots are set and it's between the firebox and damper.
• Arch Like opening.
• Firing - 48 to 60 hours.
• Cooling - 7 days.
• Although an updraft kiln tends to be less fuel efficient than a downdraft kiln, most commercially
built fuel-burning kilns are updrafts. This is mainly due to their simplicity to build, pack, and ship.

pg. 14
Fig : Intermittent Updraft Kiln
Intermittent Downdraft kiln:
• Downdraft kilns are designed to force the flame and heated air to circulate through the kiln.
Flame is introduced at the bottom of the kiln and naturally flows upward. The construction forces
the flame back downward, to exhaust at the bottom of the kiln.
• Downdraft kilns consist of four main components: the firebox, the stack area, the damper, and
the chimney. The addition of the chimney helps create draw or air flow.
• Evenly burnt.
• Better than Updraft kiln.
Fig : Intermittent Downdraft Kiln
Continuous kiln:
• In a continuous kiln, bricks are stacked in various chambers wherein the bricks undergo
different treatments at the same time. When the bricks in one of the chambers is fired, the

pg. 15
bricks in the next set of chambers are dried and preheated while bricks in the other set of
chambers are loaded and in the last are cooled.
• Eg: Bull Trench Kiln, Hoffman Kiln, Tunnel kiln
Bull Trench Kiln:
• It is an underground continuous kiln.
• The dried bricks are loaded in the kiln, the bricks are heated, then fired and then cooled and
later unloaded.
• In this kiln, there will be some wastage of fuel, since the walls and sides loose their heat in the
process of reloading and need to be heated again.
Advantages:
• Cost of fuel is less as heat of hot gases escaping through the chimney is fully utilised for
warming the bricks.
• supply of bricks is continuous.
• High percentage of First class bricks.
• Raw bricks are loaded in the kiln.
Disadvantages:
• High initial cost.
• Large amount of harmful gases are produced.
• Bricks below are under-burnt
• Skilled supervision is necessary.

pg. 16
Hoffman's Kiln:
• It is an overground continuous kiln which is used for producing continuous supply of bricks on a
large scale.
• This kiln is circular consisting of annular tunnel shaped chambers lined with fire bricks.
• There are 12 compartments having small opening at the bottom.
• The compartments have communicating doors between the chambers. These doors serve as
fuels when they are opened.
• Each compartment is connected to a fuel which passes below the chamber leading to a central
chimney.
• A leading door is provided to each compartment through which the dry bricks may be
introduced and burnt bricks may be removed.
• In this kiln, the various processes like heating, burning, cooling and finally unloading take place
simultaneously.
• Here, the fuel is economically consumed. Heat and fire can be controlled and so uniform
burning is achieved.

pg. 17
• Black smoke ejection or coal dust ejection are all eliminated.
Tunnel Kiln:
• It is a continuous type of kiln and is considered highly efficient.
• It is in the form of tunnel which may be straight, cicular or oval in plan.

pg. 18
• Tunnel is provided with rail tracks for cars.
• Tunnel is divided into three sections for working, namely pre-heating section, the burning
section and the cooling section.
• Raw bricks are loaded on trolleys and move from one end to the other end of the tunnel.
• As the bricks reach the zone of fire, they get dried and pre-heated.
• These bricks are then burnt to the required degree in the zone of fire and thereafter, they are
pushed for cooling.
• After getting adequately cooled, the bricks are unloaded.
• Uniform bricks of better quality are produced as temperature can be controlled.
• Economical when large scale bricks are to be manufactured.
Comparision between Bull Trench Kiln and Hoffman's Kiln
S.N. Bull Trench Kiln Hoffman's Kiln
1
Initial cost is low because construction is
of ordinary type.
High initial cost because construction
requires perfect designing and high quality
material.
2
Operating cost is higher because
quantity of fuel consumed is more and
conservation of heat is less.
Operating cost is lower because maximum
conservation of heat is possible in this type
of kiln.
3
Semi-continuous in strict sense because
it has no roof and cannot burn bricks
during monsoons.
Perfect continuous because it has a
permanent roof and burning operations can
be carried out throughout the year.
4 Percentage of good quality bricks is less. Percentage of good quality bricks is more.
5
Quite suitable for low investment
production of bricks.
Best suitable for semi mechanized and
mechanized production.

pg. 19
S.No. Kiln Burning of Bricks Clamp Burning of Bricks
1
The Kiln is a permanent structure
for brick burning. The bricks
should be transported from kilns
to the construction sites.
The Clamp is a temporary structure and
it can be constructed nearer to the
construction site.
2
Continuous demand for bricks
can be met.
Continuous demand for bricks cannot be
met with clamp burning.
3
Large scale projects adopt kiln
burning.
Small scale projects adopt clamp
burning.
4
The Time period of burning and
cooling is about 12 to 13 days.
The Time period of burning and cooling
is about 2 to 6 months.
5
Greater than or equal to 90%
good quality bricks can be
obtained from kilns.
Greater than or equal to 60% good
quality bricks can be obtained from
clamps.
6
Costly fuel like coal dust is used
as fuel for burning.
Low-cost fuels such as cow dung, grass,
etc. are used.
7
Fire can be controlled and the
required range of temperature
can be adjusted.
Once the burning starts, fire is not under
control which sometimes may cause
over-burning of bricks.
8
The heat generated during
burning is used to dry the raw
bricks thereby reducing the
wastage of heat.
The heat generated is wasted in case of
clamp burning.
9
Since it is a permanent structure,
the initial cost will be high.
Since it is a temporary structure, there
will be a low initial cost.
10 It requires skilled supervision. Skilled supervision is not necessary.
3.2 Other Classification of Bricks

pg. 20

pg. 21

pg. 22

pg. 23

pg. 24
3.7 Test on Bricks

pg. 25

pg. 26

pg. 27

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