Unit i bricks

BRICKS:
Composition of good brick earth
Harmful ingredients in brick earth
Classification of brick earth
Manufacture of bricks
Comparison between clamp burning & kiln
burning
Quality of good bricks
Test for bricks
Classification of bricks
Colours of bricks
Size and weight of bricks
Shape of bricks
Fire-clays
Fire-bricks
Sand-lime or calcium silicate bricks

BRICK
 The bricks are defined as artificially moulded
clay blocks with mass of natural clay with
uniform size and shape. Bricks are moulded in
rectangular shape of suitable size. Bricks are
suitably dried and brunt to gain strength,
durability etc.., to make them useful for
construction works.

Uses of bricks
 Construction of walls
 Floors
 Retaining walls
 Arches
 Columns
 Chimneys
 Other ornamental works…

COMPOSITION OF GOOD
BRICK EARTH
As per IS 2117& 1991 the clay or mixture of clay
selected should preferably confirm to the following
chemical composition for good results..
i. Clay or Alumina: 20 to 30% by weight. It absorbs
water and renders clay plastic. Excess alumina
produces cracks on drying.
ii. Silt: 20 to 35% by weight. It supports the sharp
edges of bricks and helps to remain constant
during drying and burning of bricks.

iii. Silica: 30 to 50% by weight. It retains its shape
and imparts durability and prevents cracking.
Excess of silica makes the bricks brittle and weak
on burning.
The total content of clay and silt may preferably be
not less than 50 percent by mass.
Other ingredients 1-2% by weight
i. LIME (CACO3): It prevents shrinkage on
drying and makes the brick hard. Excess lime
causes the brick to melt and hence its shape will
be lost.

ii. FERRIC OXIDE: It gives good red
color strength and durability and improves
impermeability.
iii. MAGNESIA: It effects the color and
decreases shrinkage. excess quantity leads
to decay of bricks.
iv. MANGANESE : Excess presence of
manganese makes the brick darker.
v. SODIUM POTASSIUM: Little excess of
these ingredients decolours the brick.

HARMFULINGREDIENTS IN BRICK
EARTH
 Lime-changes color
 Iron pyrites-split into pieces
 Alkaline salts-melts
 Lumps and pebbles-appearance
 Vegetation and organic matter-voids
 Salty water-patches

REQUIREMENTS OF GOOD
BRICK EARTH
 It should have required proportion of clay, sand
and other ingredients.
 It must be free from pebbles and lumps and
other organic matter.
 It should be free from harmful ingredients like
lime, alkaline salts, iron pyrites etc..,
 It should be homogeneous on through mixing.
 It should be free from lumps of lime and other
impurities.
 It should not allow more shrinkage and cracks.

Classification of brick earth
 Loamy, mild or sandy clay
Calcareous clay.
 Marls, chalky or Calcareous clay.
 Plastic, Strong or Pure clay.

Loamy, mild or sandy clay Calcareous
clay.
 The type of earth consist of
considerable amount of free silica
adding to alumina . The presence
of sand helps in such clay helps to
fuse sand and thereby to increase
hardness of brick .

Marls, chalky or Calcareous clay.
 This clay consists of considerable
amount of chalk in addition to
aluminum and silica, such clay
generally makes good bricks ,but to
avoid undesirable effects of excess
lime, the sand is sometimes added
to such clay.

Plastic, Strong or Pure clay.
 This clay consists of alumina and silica
and it is sometimes refereed to as strong
clay or fat clay. The raw bricks will
crack, shrink and wrap during drying if
pure clay alone is used In making of
bricks .
 Hence such clay is corrected by the
addition of sand and ash. the sand
prevents shrinkage and the ash provides
lime to act as flux.

MANUFACTURING OF BRICKS
1. Preparation of brick earth
2. Moulding of bricks
3. Drying of bricks
4. Burning of bricks

1.Preparation of brick earth
i. Selection of site and unsoiling.
ii. Digging.
iii. cleaning.
iv.Weathering.
v. Blending.
vi.Tempering.

 SELECTION OF SITE AND UNSOILING.
The top layer upto 20cm of the soil is taken out. This
is because the clay in the top layer is full of
impurities.
 DIGGING.
The clay is then dug from the ground.
The clay which is dug out is spread on a ground
level, just little deeper than general ground level.
The height of the heap of the clay is about 60-120cm.
 CLEANING.
The clay should be made clean from pebbles, stones
and vegetable matter. if these particles are in excess
the clay should be washed and screened, which is
considered to be uneconomical.

 WEATHERING:
The softening of clay is done by exposing it in
the atmosphere. The period of exposure varies
from weeks to full seasons.
 BLENDING:
The weathered soil is then loosened and
deposited in heaps. The ingredients of the heap
are checked to the standards.
If any ingredients required, it should be placed
in layers on the heap and blended.
Blending is the process of mixing up of all
ingredients to form homogeneity.

 TEMPERING:
In this stage the clay is brought to a proper
degree of hardness and is made fit for moulding.
Water in required quantity is added and the
whole mass is mixed so as to form a mass of
uniform character. A large scale tempering is
usually done in a pug mill.
The process of grinding clay with water and
making it plastic is known as “pugging”.

2.Moulding of bricks
Moulding is the process of making rectangular
shaped units for properly tempered clay.
1. Hand moulding.
(i) Ground moulding.
(ii) Table moulding .
2. Machine moulding.
(i) Dry press method.
(ii) Plastic method.

1. Hand moulding
(ii) Table moulding.

 In this method the ground is first
leveled and fine sand is sprinkled over
it. The mould is dipped in water and
placed over the ground. The clay is
pressed in the mould in such a way that
it fills all the concerns of the mould.
Any surplus earth from the top of the
mould is removed using cutting wire or
metal.
 Such bricks do not have frog.

(ii). Table moulding
 The process of operations are carried out on a
specially designed moulding table. the clay ,
the mould, water pots, stock board, etc are
placed on this table. the bricks are moulded
similar to the ground moulding on the table.
the cost of brick increase when table
moulding is adopted.
 Stock boards have the projections for
forming the frog.

2. Machine moulding
The moulding can also be achieved by using
machines. it is quiet economical when bricks are
produced in huge amount. this moulding is
classified into two categories.
(i) Plastic clay machines.
(ii) Dry clay machines.
This machine mould bricks have regular size ,
shape , edges and corners .They are heavier and
stronger than hand moulded bricks.

(i) Plastic clay machines .
This machines contain an opening in
rectangular shape and when we place
the tempered clay in to this machine it
will come out through this opening.
Now, the rectangular strips coming out
the opening are cut by wires to get
required thickness of brick.
So, these are also called wire cut
bricks.

(ii) Dry clay machines
 Dry clay machines are more time saving
machines. We can put the blended clay
into these machines directly without
tempering. Means tempering is also done
in this machine by adding some water.
When the required stiffness is obtained
the clay is placed in mold and pressed
hard and well-shaped bricks are
delivered. These are called pressed bricks
and these do not require drying they may
directly sent to burning process.

3.Drying
 The object of drying bricks is to remove the
moisture to control shrinkage and to save both
fuel and time during burning.
 Drying is essentially evaporation of moisture
either in a normal atmosphere or with
controlled humidity and temperature.
 Drying is slow, otherwise cracks may develop
on its surface. The process is usually take a
number of days (3 to 10 days).

Drying
1. Natural drying
2. Artificial drying

Natural drying
 The main advantage of natural drying
over artificial drying is the saving of
fuel.
 Drying is usually done by placing the
bricks in sheds with open sides so as
to ensure free circulation of air and
protection from bad weather and
rains. The bricks are allowed to dry
till they are left with 5 to 7 percent
moisture content.

 Slop-moulded bricks must be
dried in single layers as they
cannot bear the weight of other
bricks without distorting.
 Sand-moulded bricks, being
more firm than slop-moulded
bricks, are not likely to pick up
debris or to distort easily.

Artificial drying
 When the bricks are to be dried rapidly
on a large scale , the artificial drying is
adopted.
 The temperature is usually less than
120 degree C
i. Tunnel drier.
ii. Hot floor drier.

Tunnel drier.
 In the tunnel dryer , the bricks are filled, dried and
emptied in rotation.
 The tunnel dryers are economical .
 where bricks are put on rolled boards,The boards
are passed through heated tunnels, and when dry
are carried direct to the kiln.
Hot floor drier.
 In this floor is heated by a system of flues passing
under it, from furnaces at one end to stack at the
other end.
 In the hot floor drier the loading of bricks is done at
one end and they are taken out at other end.

4. Burning of bricks
 In the process of burning, the dried bricks are
burned either in clamps (small scale) or kilns
(large scale) up to certain degree temperature. In
this stage, the bricks will gain hardness and
strength so it is important stage in manufacturing
of bricks.
 The temperature required for burning is about
1100oC. If they burnt beyond this limit they will
be brittle and easy to break. If they burnt under
this limit, they will not gain full strength and there
is a chance to absorb moisture from the
atmosphere.

Burning in Clamp
 The bricks and fuel are placed in alternate layers.
The amount of fuel is reduced successively in the
top layers. Each brick tier consists of 4–5 layers of
bricks. Some space is left between bricks for free
circulation of hot gasses. 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.
The production of bricks is 2–3 lacs and the
process is completed in six months. This process
yields about 60 per cent first class bricks.

Kiln Burning
Intermittent Kiln:
 The example of this type of an over
ground, rectangular kiln is shown in
Fig. 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.

Continuous Kiln:
 The examples of continuous kiln are
Hoffman’s kiln and Bull’s trench kiln .In a
continuous kiln, bricks are stacked in
various chambers where in the bricks
undergo different treatments at the same
time. When the bricks in one of the
chambers is fired, the 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.

COMPARISON OF BURNING OF
BRICKS

QUALITY OF GOOD BRICKS
 Colour.
 Size and Shape.
 Texture.
 Hardness.
 Soundness .
 Durability.
 Porosity.
 Crushing Strength.
 Presence of soluble salts.
 Resistance to fire.
 Brick earth.

 Colour:
Good brick should be well burnt and should
have uniform copper colour.
Over burnt and under burnt bricks losses
uniformity of colour on its surface and its
strength. Good quality bricks should always be
of uniform colour throughout.

 Size and Shape: The bricks should have uniform
size and plane, rectangular surfaces with parallel
sides and sharp straight edges.

 Texture : The surfaces should not be too
smooth to cause slipping of mortar. The brick
should have precompact and uniform texture. A
fractured surface should not show fissures,
holes grits or lumps of lime.
 Hardness : The brick should be so hard that
when scratched by a finger nail no impression is
made.
 Soundness : When two bricks are struck
together, a metallic sound should be produced.
 Durability : The good bricks should be able to
resist, the effects of weathering agencies like
wind, rain, temperature variations etc.

 Porosity: Water Absorption should not
exceed 20 per cent of its dry weight
when kept immersed in water for 24
hours.
 Crushing Strength: Crushing strength
should not be less than 10 N/mm2.
The bricks should not break into pieces,
when dropped from the height of one
meter.

 Presence of soluble salts : Soluble salts, if
present in bricks, will cause efflorescence on
the surface of the bricks.
The bricks, when soaked in water for 24 hours,
should not show deposits of white salt when
allowed to dry in shade.

 Resistance to fire : The good bricks
have to resist temperature upto 1220D.c.
 Brick earth : Brick earth should be free
from stones, kankars, organic matter etc.

TEST FOR BRICKS
 I S 3495 - 1992
METHODS OF TESTS OF BURNT CLAY
BUILDING BRICKS
PART 1 : Determination of compressive strength
PART 2 : Determination of water absorption
PART 3 : Determination of efflorescence
PART 4 : Determination of warpage

1. Determination of compressive
strength
 The brick specimen are immersed in water
for 24 hours.
 The frog of the brick is filled flush with 1:3
cement mortar and the specimen is stored in
damp jute bag for 24 hours and then
immersed in clean water for 24 hours.
 The specimen is placed in compression
testing machine with 6 mm plywood on top
and bottom of it to get uniform load on the
specimen.

 Then load is applied axially at a uniform rate
of 14 N/mm2 .
 The crushing load is noted.
 Then the crushing strength is the ratio of
crushing load to the area of brick loaded.
Average of five specimen is taken as the
crushing strength.
not less than
 1st class bricks-10.5 N/mm2
 2nd class bricks-7.0 N/mm2
 3rd class bricks-5.0 N/mm2

2. Determination of water absorption.
 The bricks are put in an oven at a
temperature of 105dC for drying.
 Bricks are weighed in a digital
weighing machine and is record asW1
 The bricks are immersed in water at
room temperature for 24 hours.

 After 24 hours immersion, the bricks
are taken out of water and wiped with
a damp cloth for 3 minutes.
 The bricks are weight again and
recorded as W2.
 Water absorption in % is calculated as
(𝑊2−𝑊1 ) 𝑊1 × 100

3.Determination of efflorescence
 Place the brick specimen in a glass dish
containing water to a depth of 25 mm in
a well ventilated room. After all the
water is absorbed or evaporated again
add water for a depth of 25 mm. After
second evaporation observe the bricks for
white/grey patches.
 The observation is reported as ‘nil’,
‘slight’, ‘moderate’, ‘heavy’ or serious.

(a) Nil: No patches
(b) Slight: 10% of area covered with
deposits
(c) Moderate: 10 to 50% area covered with
deposit but unaccompanied by flaking of
the surface.
(d) Heavy: More than 50 per cent area
covered with deposits but unaccompanied
by flaking of the surface.
(e) Serious: Heavy deposits of salt
accompanied by flaking of the surface.

 TESTING:-
 a. FOR CONCAVE WARPAGE: - Place the
flat surface along the surface to be measured
selecting the location that gives the greatest
departure from straightness. Measure the
greatest distance of the brick surface from the
edge of straightness by a steel rule of wedge.
 b. FOR CONVEX WARPAGE: - Place the
brick on the flat surface with the convex surface
in contact with the flat surface. Measure the
distance from flat surface to the four corner of
the brick, and take the maximum of four
measurement.

5. Dimensions and tolerance test
IS 1077 : 1992 common burnt clay building bricks
– specification
To perform this test, select 20 bricks randomly
from brick group and stack them along its length
, breadth and height and compare.

CLASSIFICATION OF BRICKS
 Classification of clay bricks bases on field
practice.
 Classification of clay bricks bases on
strength.
 Classification of bricks based on shape.
 Classification of bricks based on their using.
 Classification of bricks based on finish.
 Classification of bricks based on
manufacturing.
 Classification of bricks based on burning.

Classification of clay bricks bases on
field practice
 a. First Class Bricks:
 b. Second Class Bricks:
 c. Third Class Bricks:
 d. Fourth Class Bricks:

a. First Class Bricks:
 These are thoroughly burnt and are of deep
red, cherry or copper colour.
 The surface should be smooth and
rectangular, with parallel, sharp and straight
edges and square corners.
 These should be free from flaws, cracks and
stones.
 These should have uniform texture.
 No impression should be left on the brick
when a scratch is made by a finger nail.
 The fractured surface of the brick should not
show lumps of lime.

 A metallic or ringing sound should come
when two bricks are struck against each
other.
 Water absorption should be 12–15% of its
dry weight when immersed in cold water for
24 hours.
 The crushing strength of the brick should not
be less than 10 N/mm2.
 Uses: First class bricks are recommended for
pointing, exposed face work in masonry
structures, flooring and reinforced brick
work.

b. Second Class Bricks:
 These are supposed to have the same
requirements as the first class ones except that
 Small cracks and distortions are permitted.
 A little higher water absorption of about 16–20%
of its dry weight is allowed.
 The crushing strength should not be less than 7.0
N/mm2.
 Uses: Second class are recommended for all
important or unimportant hidden masonry works
and centring of reinforced brick and reinforced
cement concrete (RCC) structures.

c. Third Class Bricks:
 These bricks are under burnt.
 They are soft and light-colored.
 They produce a dull sound when
struck against each other.
 Water absorption is about 25 per cent
of dry weight.
 Uses: It is used for building temporary
structures.

d. Fourth Class Bricks:
 These bricks are over burnt.
 Badly distorted in size and shape.
 Brittle in nature.
 Uses: The ballast of such bricks is
used for foundation and floors in lime
concrete and road metal.

Classification of clay bricks bases on
strength.
a. Heavy duty bricks.
The burnt clay bricks having compressive
strength more than 40.0 N/mm2 are known as
heavy duty bricks.
Uses: For masonry items in heavy structure like
bridges foundations for industrial buildings for
b. Light duty bricks.
The burnt clay bricks having compressive
strength less than 40.0 N/mm2 are known light
duty bricks.
Uses: less importance works, compound walls etc.

Classification of bricks based on shape.
 A. Subclass ‘A’ bricks : These bricks should
have smooth rectangular faces with sharp
corners and uniform colour.
 B. A. Subclass ‘B’ bricks : These bricks have
slight distorted and round edges.

Classification of bricks based on their using.
a. Common Bricks:
This is a general multi-purpose unit
manufactured economically without special
reference to appearance.
used for filling, backing and in walls where
appearance is negligible.
b. Facing Bricks:
These are made primarily with a view to have
good appearance, either of colour or texture or
both.
used in fronts of building walls

 c. Engineering Bricks:
These are strong, impermeable,
smooth, table moulded, hard and
conform to defined limits of
absorption and strength. These are
used for all load bearing structures.

Classification of bricks based on finish.
a. Rustic Bricks
Rustic bricks are mechanically textured finish and
varying pattern
b. Sand faced bricks
Sand faced bricks has texture surface made by
sprinkling by sand inside the mould.

Classification of bricks based on
manufacturing.
 A. Hand moulded bricks:
These bricks are moulded by hand.
 B. Machine moulded bricks:
These bricks are moulded by Machine.
i.Wire cut bricks.
ii. Pressed bricks.

Classification of bricks based on
burning.
 A. Pale bricks:
These bricks are unburnt.
 B. Body bricks:
These bricks are well burnt occupying central
position of the kiln.
 C. Arch bricks:
These bricks are over burnt also known as
clinker bricks.

COLOURS OF BRICKS
The colours of bricks depends upon the following
factors.
1. Degree of dryness achieved before burning.
2. Natural colour of raw materials.
3. Due to its chemical composition.
4. Nature of sand used for moulding operations.
5. Quality of fuel used for burning.
6. Quantity of air admitted to the kiln during
burning.
7. Temperature at which the bricks are burnt.

 Ex : Pink bricks are the result of a high iron
content.
white or yellow bricks have a higher lime
content.
As the temperature is increased the colour
moves through dark red, purple, and then to
brown or grey at around 1,300 °C

SIZEAND WEIGHT OF BRICKS
 In India, standard brick size is 190 mm x 90
mm x 90 mm as per the recommendation of
BIS. With mortar thickness, the dimension of the
brick becomes 200 mm x 100 mm x 100
mm which is also known as the nominal size of
the modular brick.
 The permissible tolerance as stated in code are
 Dimension (mm) —————- Tolerance (mm)
 190 ——————————— +or - 3 mm
 90 ———————————— + or - 2 mm
 40———————————— + or - 2 mm
 The weight of standard brick shall be of around
3 kg.

SHAPE OF BRICKS
 Bullnose brick: A brick moulded with a
rounded angle is termed as a bullnose. This type
of brick is used for a rounded quoin. A
connection which is formed when a wall takes a
turn is known as quoin.

 Channel bricks: These types of bricks are
moulded to the shape of a gutter or a
channel and they are often glazed. These
bricks are used to function as drains.

 Coping Bricks:
Coping bricks are used where the coping is to be
provided. The shapes of brick can be chamfered,
half round or saddle-back.
Uses: Coping bricks are used as topmost
direction on parapets.

 Hollow Bricks:
Hollow bricks are also known as the cellular or
cavity bricks.They are made up of special
homogeneous clay. Hollow bricks are light in
weight.
Uses: Hollow bricks are used in the partition
wall.

 Paving Bricks:
Paving bricks are made up of clay with a higher
percentage of iron. Such bricks resist better the
abrasive action of traffic.
Uses: Paving bricks are most commonly used
for street pavements, garden walks, stable floors,
etc.

 Perforated Bricks:
Perforated bricks have cylindrical holes
throughout their thickness. These bricks are
light in weight and they require less quantity of
clay for their preparation.
Uses: The perforated bricks are used in the
panel of lightweight structures and multi-
storeyed framed structures.

FIRE-CLAYS
 Fire clay is a range of refractory clays used
in the manufacture of ceramics,
especially fire brick.
 The refractory clay is composed of heat
resisting materials such as silica, alumina,
bauxite, magnesite, chromite etc. and does
not contain metallic oxides such as oxide of
iron, lime and alkalies.
 High-grade fire clays can withstand
temperatures of 1,775 °C.

FIRE-BRICKS
 Firebricks, or refractory bricks are defined as
non metallic material suitable for the
construction of launching of furnaces
operated at high temperatures.
 These are made up of refractory clays.
MANUFACTURING:
 Similar to clay bricks but the clay used is fire
clay.
 Burning is at high temperature in special kilns.
(Hoffmans kiln).

PROPERTIES REFRACTORY BRICKS
 The colour is whitish, yellow or light brown.
 Water absorption varies 5 to 10%.
 The compressive strength ranges between 150 to
200 N/mm2.
USES
 Lining of blast furnace.
 Ovens.
 Kilns.
 Boilers.
 Chimneys.

Classification of Refractory
Brick
 Acid bricks.
i. Fire bricks.
ii. Silica bricks.
 Basic bricks.
 Neutral bricks.
i. Chromite bricks.
ii. High alumina bricks.

 Acid bricks
These are used in areas where slag and
atmosphere are acidic.
They are stable to acids but attacked by
alkalis.
Fireclay Bricks is made of mullite
(25~50%), glass phase (25~60%) and
cristobalite and quartz (reachable 30%).
Fireclay brick is used in blast furnace,
hot blast stove, heating furnace, power
boiler, lime kiln, rotary kiln, ceramic kiln
and refractory bricks calcining kiln.

 Silica Bricks, a kind of main acid refractory
brick, is made of over 93% SiO2 content.
Used to build coke oven, and also is used for all
kinds of glass furnace, ceramic, carbon
calcinations furnace.
Basic bricks.
These are used on areas where slag and
atmosphere are basic, they are stable to alkaline
slag, dust and furnace at the elevated
temperatuures.

 Neutral bricks.
These are chemically stable to both acids and
bases and used in areas where slag and
environment are either acidic or basic.
i. Chromite bricks.
These are prepared from a mixture of
chrome, iron ore, ferrous oxide, bauxite and
silica.
ii. High alumina bricks.
Contain high percentage of alumina.
High alumina refractory bricks are widely
used Iron and Steel Industry, non-ferrous metals
industry and other industries

SAND-LIME OR CALCIUM
SILICATE BRICKS
 Calcium silicate bricks are made of sand and lime
and popularly known as sand lime bricks.
 These bricks are used for several purposes in
construction industries such as ornamental works
in buildings, masonry works etc.
Materials Used
 Sand
 Lime
 Water
 Pigment

 Sand
Calcium silicate bricks contains high amount
of sand is about 88 – 92%. It means the
properties of these bricks depends upon the
characteristics of sand used.
 Lime
Lime content in calcium silicate bricks varies
from 8 to 12%. The lime used shall be of good
quality and high calcium lime.
 Water
Clean water should be used for preparing
calcium silicate bricks.

 Pigment
Pigments are generally used to give color to the
bricks.They are added to the sand and lime
while mixing.
Total weight of brick contains 0.2 to 3 % of
pigment quantity.

Advantages
 Mortar required for providing plaster on calcium
silicate bricks is very less.
 Color and texture of these bricks is uniform.
 Compressive strength of sand lime bricks is about
10N/mm2
 For constructions in clay soils, these bricks are more
preferable.
 Trouble of Efflorescence does not arise in the case
of sand lime bricks.
 These bricks have great fire resistance and water
repellant properties.
 Cost of construction gets reduced about 40%

Disadvantages
 These are not suitable for laying foundation,
because they cannot provide resistance to
water for longer period.
 They cannot also resist fire for longer periods
so, they are not suitable for building furnaces
etc.
 Abrasion resistance of these bricks are very
less so, they cannot be used as paving
materials.

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