Bricks are one of the oldest and most widely used construction materials. They are durable, lightweight, fire resistant, and cheaper than stones to use for building. A good quality brick is made from a mixture of clay and sand that is molded, dried, and fired at a high temperature. This makes the brick hard and long-lasting. Bricks are commonly used to construct walls, bridges, floors, and other structural elements in buildings. They have advantages over other materials like stones in being easier to work with and transport. Proper analysis and processing of the clay mixture is important to produce high quality bricks with good compressive strength, low water absorption, and resistance to cracking.

1. Bricks
Dr. Shahid Ali

3. BRICKS :
• One of the oldest construction material
• Most popular and leading construction
material
REASON:
• Low cost
• Durable
• Light weight
• Easy to work with
ADVANTAGES OVER STONES:
• Light weight
• Uniform shape and size
• Moulded to required size
• Easy laying
• Cheaper
• Fire resistance
• Thinner sections
• Less mortar for bonding
• Easy transportation
• Produced in large quantities
• A brick is an artificial kind of stone made of clay whose chief characteristics are a
plasticity when wet and stone like hardness after being heated to high temperature.

4. Factors that affect the quality of Bricks:
• Chemical properties of the clay used for preparation of the clay
• Process of drying
• Different degrees of burning
Constituents of Brick clay and their functions:
• A good brick-clay should be such a mixture of pure clay and sand that when prepared with water, it can easily be
moulded and dried without cracking or warping.
 Chemical analysis of a good brick-clay should give the following percentage of chemical composition:
Silica 55%
Alumina 30%
Iron oxide 8%
Magnesia 5 %
Lime 1 %
Organic matters 1%
---------------
100%

6. • Bricks dated 10,000 years old were found in the Middle East.
• The first sun-dried bricks were made in Mesopotamia (what is now Iraq), in the ancient city of Ur in about 4000 BC

7. 1.Bricks are extensively used as BUILDING blocks
2.First class Bricks are used in ARCHITECTURAL compositions and face work of a structure.
3.Fire Bricks are used for lining of evens , furnaces , chimneys etc.
4.Bricks are used for sewer lining.
5.Bricks are also used for foot-paths and paving
6.The first class and second class bricks are widely used for all sorts of sound work i.e. buildings, roads,
dams , bridge piers, tunnels, pitching works etc.
7.The third class bricks are used for temporary buildings.
8.The fourth class bricks are used as road metal and as ballast which is used in foundations, floors, roofs
etc.
Uses of Bricks
• Walls, Bridges, Dams and Culverts Pavements, Kerbs Partitions and roads
• Fire bricks used for fire resisting structures
• Ornamental works
• Perforated and hollow bricks for heat insulation
• Compound walls, Columns, Stairs and Arches
• Broken pieces for weathering courses

8. Advantages of bricks :
* Brick will not burn, buckle or melt.
* Brick will not rot and allow Termites to invade.
* Brick will not rust and corrode.
* Brick will not dent.
* Brick will not fade from the Sun's UV Rays.
* Brick will not be damaged by high winds, rain or hail.
* Brick will not require constant maintenance.
* Brick will not devalue.
* Brick will not limit your personal expression.
* Brick will not limit your design options.

9. MANUFACTURE OF BRICKS:
• Preparation
• Moulding
• Drying
• Burning
PREPARATION:
• Upper layer removed ( free from vegetation, gravel and lime)
• Clay exposed to atmosphere in wet condition
• Clay mixed with ingredients to become homogeneous and attain uniform colour
• Clay mix kneaded for moulding
MOULDING:
• Steel or wooden moulds Open both at top and bottom
• Prepared according to size of brick
• Clay mix filled in the mould, levelled and excess qty. is removed.
• Mould is lifted up and the procedure is repeated.

10. USES:
• Walls, Bridges, Dams and Culverts Pavements, Kerbs Partitions and roads
• Fire bricks used for fire resisting structures
• Ornamental works
• Perforated and hollow bricks for heat insulation
• Compound walls, Columns, Stairs and Arches
• Broken pieces for weathering courses
DRYING:
 Moulded bricks are stacked in layers
 Dried for about 6 weeks (depending on weather condition)
BURNING:
• Clamps (or) Kilns are used to burn
• Stacked and burnt at about 8000 C using coal, firewood etc.
• Burning imparts strength and hardness
• It should be properly burnt
• Over-burnt leads to brittleness
• Under-burnt leads to softness and hence less load carrying capacity

11. CLASSIFICATION:
BASED ON THE MANUFACTURING PROCESS
 FIRST CLASS BRICKS
 SECOND CLASS BRICKS
 THIRD CLASS BRICKS
 FOURTH CLASS BRICKS
FIRST CLASS BRICKS:
• Smooth and rectangular
• Parallel, sharp and straight edges
• Thoroughly burnt with deep red colour
• Uniform texture
• Water absorption 12% to 15% of its dry weight when immersed in cold water for 24 hrs
• Mettallic (or) Ringing sound by striking
• Crushing strength not less than 10.5 N/mm2
SIZE AND WEIGHT:
• 19 cm x 9 cm x 9 cm
• 20 cm x 10 cm x 10 cm (including mortar)
• 3 to 3.5 kg

12. SECOND CLASS BRICKS:
• Small cracks are allowed
• Water absorption 16% to 20%
• Crushing strength not less than 7 N/mm2
• USES: all masonry works
THIRD CLASS BRICKS:
• Under burnt
• Soft and light
• Dull sound
• Water absorption is 25%
• USES: Temporary structures
FOURTH CLASS BRICKS:
• Over burnt
• Bad shape and size
• brittle

13. QUALITY OF GOOD BRICKS:
• Shape and size: Uniform with straight edges
• Colour: Deep RED
• Texture and Compactness: No fissures and holes
• Hardness and Soundness : No finger nail impression
• Compressive strength: [ 10.5 N/mm2]
• Water absorption: [ Not more than 20%]
Density: [ 17 to 19 kN/m3 ]
Shear strength: 5 To 7 N/mm2
Fire Resistance: High
Soluble salts: Free
Breakage: When dropped from 1m height it should not break.

14. TESTS ON BRICKS:
1. COMPRESSIVE STRENGTH
• Both faces made smooth
• Immersed in water for 24 hrs for three days
• The specimen is then placed between the plates of the compression testing machine
• Load is applied axially at a uniform rate 14 N/mm2and maximum load at which the specimen fails
is noted for determination of compressive strength not less than 3.5 N/mm2
• Again immersed in clean water for 3 days
• Tested in compression testing machine.
• Compressive strength = Load at failure/ Area of the cross section of the brick

15. 2.WATER ABSORPTION TEST:
• Dry brick weighed (W1)
• Immersed in water for 24 hrs
• Again weighed (W2)
• Percentage of water absorption = ([W2 – W1]/ W1 )X 100
3.EFFLORESCENCE TEST:
• Bricks placed in water of 2.5 cm depth till water is absorbed or evaporated
• After drying again placed in water
• Examined for efflorescence
• Efflorescence is classified as follows:
• Nil 0%
• Slight 10%
• Moderate 10 to 50%
• Heavy more than 50%

17. Composition Following are the constituents of good brick
earth.
Alumina
• A good brick earth should contain 20 to 30 percent of alumina.
• If alumina is present in excess, raw bricks shrink and warp
during drying and burning.
Silica
• A good brick earth should contain about 50 to 60 percent of
silica.
• Silica exists in clay either as free or combined form.
• It thus imparts uniform shape to the bricks.
Oxide of iron
• A small quantity of oxide of Iron -- 5 to 6 percent is
desirable in good brick to imparts red colour to bricks.
• Excess of oxide of iron makes the bricks dark blue or
blackish.
Magnesia
• A small quantity of magnesia in brick earth imparts
yellow tint to bricks
• decreases shrinkage.
• excess of magnesia leads to the decay of bricks.
 The ingredients like, lime, alkalies, pebbles, organic
matter should not present in good brick earth
• Silica exists in all clays in a state of chemical combination with
alumina forming silicate of alumina and some times exists in a
free state when it is called sand. The presence of sand
prevents cracking, shrinking and warping. The higher the
proportion of sand, the more shapely and uniform in texture
shall be the brick. But too much of sand makes the brick brittle
and weak.
• This is the principal constituent of brick clay. It imparts
plasticity to clay which is very essential for the purpose of
moulding. It also imparts density..
• The presence of iron oxide in clay enhances the
impermeable and durable qualities. Iron and lime in
small quantities give creamy color to bricks. The color
of bricks is very much dependent upon the contents of
iron and the color ranges from light yellow to orange
and red.

18. Lime
• A small quantity in finely powdered state prevents shrinkage of raw bricks.
• Excess of lime causes the brick to melt and hence, its shape is lost due to the splitting of brick
• It reduces shrinkage of bricks during drying and enables the silica to melt in burning and thus binds the particles of brick
together. In excess, however, it will cause the brick to fuse too readily and the shape will be lost.
Alkalies and Organic matter:
• A small quantity of organic matter will assist burning bricks. Excess is bad, because if it is not completely burnt, the
bricks will be porous.
• Small quantity of alkalies will lower the fusion point of clay.

19. Harmful constituents of Brick-clay
Iron Pyrites: (FeS2)
Presence of pyrites causes crystallization and disintegration of bricks on burning.
Alkalies:
They are mainly the chlorides and sulphates of calcium, magnesium, sodium and potassium. They produce a dark
greenish hue on the surface of bricks on drying. They cause the bricks to fuse, twist and warp during burning. Alkalies in
bricks absorb moisture from atmosphere and on drying cause efflorescence.
Efflorescence – If soluble salts are present in bricks they absorb moisture from atmosphere and go into solution which
appears on the surface in the form of whitish substance as the moisture dries out and the salt crystallize.
Stone particles:
Small particles of stones do not allow the clay to be mixed thoroughly and uniformly. These are harmful to the
uniformity of brick texture. These make bricks porous and weak.
Vegetation and Organic matter:
They make the bricks porous and weak because vegetations and organic matter get burnt during the burning of bricks
leaving small pores in them.
Lime:
If Lime present in excess amount causes the brick to fuse too readily and the shape is lost. Lime in the form of limestone
and kankar nodules is very harmful and cause serious troubles to bricks such as it causes the bricks to split and crumble
to pieces and deteriorates the quality of a good brick.

20. Carbonaceous Materials in the form of bituminous matter or carbon greatly affects the colour of raw clay. Unless
proper precaution is taken to effect complete removal of such matter by oxidation, the brick is likely to have a black
core
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 decolored by white blotches.
Water A large proportion of free water generally causes clay to shrink considerably during drying, whereas combined
water causes shrinkage during burning. The use of water containing small quantities of magnesium or calcium
carbonates, together with a sulphurous fuel often causes similar effects as those by sulphur.

21. Manufacture of bricks:
The manufacturing of brick,
the following operations are
involved
• Site selection
• Preparation of brick
earth
• Moulding of brick
• Drying of bricks
 Selection of site
• Must have suitable clay In sufficient quantity
• Location---water table should be atleast 1m below kiln floor
 Preparation of clay :-
The preparation of clay involvesfollowing operations
 Unsoiling
Top layer of 20cm depth is removed as it contain impurities-organic matter, roots.
 Digging
Clay is dug out from ground and spread on level ground about 60cm to 120cm heaps.
 Cleaning
Stones, pebbles, vegetable matter etc removed and converted into powder form.
• Unsoiling
• Digging
• Cleaning
• Weathering
• Grinding
• Blending
• Tempering

26. Weathering
Clay is exposed to atmosphere from few weeks to full season.
Grinding
hard clay with lumps are crushed in clay crushing rollers
Blending
Clay is made loose and any ingradient to be added to it is spread out at top and turning it up and down in vertical
direction
Tempering
 Clay is brought to a proper degree of hardness,
 then water is added to clay and
 whole mass is kneaded or pressed under the feet of men or cattle for large scale,
 done in pug mill

30. Molding Table

33. Moulding of bricks Hand or machine Mould- Rectangular boxes open at bottom Wood or steel
Hand moulding
• Ground is levelled
• Sprinkle fine sand
• Dip mould in water and place on ground
• Lumps of clay are dashed in to it
• Pressed and filled----fill corners
• Surplus clay removed by using a stricker
• Mould is lifted up
• Raw brick remains
Machine moulding
When, -large scale production- Clay is hard
Plastic clay machine---wire cut bricks
Dry clay machine---powdered clay filled in moulds ---pour water----pressed----results in hard, well shaped

37. Burning
The burning of clay may be divided into three main stages.
Dehydration (400-650°C) This is also known as water smoking stage.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. Too rapid heating causes cracking or bursting of the bricks.
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.
Oxidation Period (650-900° C) During the oxidation period, (1) remainder of carbon is eliminated and, (2) the ferrous iron
is oxidized to the ferric form. The removal of sulphur is completed only after the carbon has been eliminated. Sulphur on
account of its affinity for oxygen, also holds back the oxidation of iron.
Consequently, in order to avoid black or spongy cores, oxidation must proceed at such a rate which will allow these
changes to occur before the heat becomes sufficient to soften the clay and close its pore. Sand is often added to the raw
clay to produce a more open structure and thus provide escape of gases generated in burning.
Vitrification — To convert the mass into glass like substance — the temperature ranges from 900-1100°C for low melting
clay and 1000- 1250°C for high melting clay. Great care is required in cooling the bricks below the cherry red heat in order
to avoid checking and cracking. Vitrification period may further be divided into (a) incipient vitrification, at which the clay
has softened sufficiently to cause adherence but not enough to close the pores or cause loss of space — on cooling the
material cannot be scratched by the knife; (b) complete vitrification, more or less well-marked

38. by maximum shrinkage; (c) viscous vitrification, produced by a further increase in temperature which results in a soft
molten mass, a gradual loss in shape, and a glassy structure after cooling. Generally, clay products are vitrified to the
point of viscosity. However, paving bricks are burnt to the stage of complete vitrification to achieve maximum hardness
as well as toughness.
Burning of bricks is done in a clamp or kiln. A clamp is a temporary structure whereas kiln is a permanent one.
Burning in Clamp or Pazawah A typical clamp is shown in Fig. 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 cowdung 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.

40. 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.
If the process of burning bricks is discontinuous, the kiln is known as intermittent kiln

41. Continuous Kiln : Hoffman's kiln and Bull's trench 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 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.
The kiln used for burning bricks may be underground, e.g. Bull’s trench kiln or overground, e.g. Hoffman's kiln. These
may be rectangular, circular or oval in shape. When the process of burning bricks is continuous, the kiln is known as
continuous kiln, e.g. Bull's trench and Hoffman's kilns.
Hoffman's Continuous Kiln

43. Bull's Trench Kiln

47. Drying:
• The damp bricks, if burnt, are likely to be cracked and distorted. Hence moulded bricks are dried
• Bricks are laid along and across the stock in alternate layers.
• 5-7 % moisture content
• Mostly natural or artificial drying
Burning: to impart hardness, strength and makes them dense and durable.
• Burning --- clamps or in kilns.
• Clamps are temporary structures and to manufacture bricks on small scale.
• Kilns are permanent structures and they are adopted to manufacture bricks on a large scale.
Clamp
• Temporary structures
• Stacked in layers with gaps for firewood
• 6-8 weeks
• Strong tough bricks
• Quality not uniform
• No skilled labour
Kilns
• Masonry structures ----permanent
• Continuous
• Uniform quality
• Need skilled labour

48. Qualities of Good Brick
• bright homogeneous and compact structure free from voids should not absorb water more than 20 percent by
weight for first class bricks
• 22 percent by weight for second class bricks when soaked in coldwater for a period of 24 hours
• Bricks should be uniform in color, size and shape.
• They should be sound, hard, well burnt and compact.
• They should be free from cracks and other flaws such as air bubbles, stone nodules, holes, grit of lime etc.
• The compressive strength of bricks should be in the range of 5000 to 8000 psi.
• The percentage of soluble salts (sulphates of calcium, magnesium, sodium and potassium) should not exceed 2.5% in
burnt bricks, because the presence of excess soluble salt causes efflorescence.
• They should be neither over burnt nor under burnt.
• Their weight should be generally 6 lbs per brick and the weight per cu ft should not be less than 125 lbs.
• They should have low thermal conductivity as it is desirable that the buildings built of them should be cool in
summer and warm in winter.
• They should be non-inflammable and incombustible.
• Bricks should not change in volume when wetted.

49. Field tests of bricks: To determine the quality of good bricks:
• Take a brick and try to make mark on the surface by nail. If you can make it, it is not a good brick. If not, it is very
hard and compact.
• Take a brick and strike it with a hammer, if it gives clear ringing or metallic sound, it is a good brick.
• Take two bricks and form a tee (T) and drop from a height of 6ft on a more or less solid surface. If they break, they
are not good bricks. If they remain unbroken, they are good bricks
Size of Bricks:
According to P.W.D specification the standard size of bricks in our country is 9.0” X 4.5” X 3”. This size is most
economical.

50. Tests on bricks
A brick is generally subjected to following tests to find out its suitability of the construction work.
• Compressive strength
• Absorption
• Hardness
• Presence soluble salts
• Shape and size
• Soundness
• Structure
A good should not absorb not more than 20 percent of weight of dry brick
Absorption
Oven dried for 270 C for 24 hrs
A good should not absorb not more than 20 percent of weight of dry brick
%water absorption = ((w2-w1)/w1) X 100
Hardness
Scratch with finger nail -- No impression is left on the surface the brick is treated to be sufficiently hard

51. Presence of soluble salts (efflorescence)
The bricks should not show any grey or white deposits after immersed in water for 24 hours (HW)
Shape and size
It should be standard size and shape with sharp edges
Soundness
The brick should give clear ringing sound struck each other
Structure
The structure should be homogeneous, compact and free from any defects

53. A pugmill or pug mill is a machine in which clay or other materials are mixed into a plastic state. Industrial
applications are found in pottery, bricks, cement and some parts of the concrete and asphalt mixing processes.
A pugmill may be a fast continuous mixer

55. Drawings of the intermittent and continuous ovens. The arrows indicate the flow of brick loads and gas flow.
(a) Open kiln without fixed walls (rectangular), (b) open kiln with fixed walls, (c) open kiln without fixed walls
(cylindrical), (d) down-draught, (e) MK, (f) dome, (g) Hoffman, (h) Bull's Trench, (i) Cedan, (j) multi-chambers,
(k) zigzag, (l) mobile-modular, (m) vertical shaft and (n) tunnel.