This document provides information about bricks, including their types, characteristics, classification based on quality, and manufacturing processes. It discusses the different classes of bricks from first to fourth class based on their quality. It also outlines the key properties that good bricks should have, such as uniform color, standard size and shape, fine texture, hardness, strength, and resistance to water absorption and efflorescence. The document explains the traditional and modern methods used to manufacture bricks, including molding and firing processes.

1. BRICKS
(Types, Characteristics, Classification, Quality Tests)
TEACHER: Madam Rabia
SUBJECT: Engineering Materials
BATCH: 13
BY:LATEEF HYDER WADHO
ROLLNO:K13-CE-19
4/1/2013
2013
DEPARTMENT OF CIVIL ENGINNERING
ASSIGNMENT No:2
2222212NONO:
MEHRAN UNIVERSITY OF
ENGINEERING AND TECHNOLOGY
KHAIRPUR MIR’S

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BRICKS
Brick is obtained by moulding good clay into a block, which is dried and then burnt. This is the
oldest building block to replace stone. Manufacture of brick started with hand moulding, sun
drying and burning in clamps. A considerable amount of technological development has taken
place with better knowledge about to properties of raw materials, better machinaries and
improved techniques of moulding drying and burning. The size of the bricks are of 90 mm × 90
mm × 90 mm and 190 mm × 90 mm × 40 mm. With mortar joints, the size of these bricks are
taken as 200 mm × 100 mm × 100 mm and 200 mm × 100 mm × 50 mm.
Uses of Bricks
Bricks are used in the following civil works:
(i) As building blocks.
(ii) For lining of ovens, furnaces and chimneys.
(iii) For protecting steel columns from fire.
(iv) As aggregates in providing water proofing to R.C.C. roofs.
(v) For pavers for footpaths and cycle tracks.
(vi) For lining sewer lines.
—————Types of Bricks
—————Properties of Bricks
—————Tests on Bricks
—————Classification of Bricks Based on-their Quality
Classification of Bricks
The bricks usedin constructionareclassified as:
(I) Firstclass bricks
(ii) Secondclass bricks
(iii) Third class bricks
(IV) Fourthclassbricks
(I) First Class Bricks: These bricks are of standard shapeand size. Theyare burnt in kilns. They
fulfill alldesirablepropertiesof bricks.
(ii)Second Class Bricks: These bricks are ground moulded and burnt in kilns. The edgesmay
not besharp and uniform. Thesurface may be some what rough. Such bricks are commonly
used for theconstruction of walls which are going to be plastered.
(iii)Third Class Bricks: These bricks are ground moulded and burnt in clamps. Their edgesare

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somewhat distorted.Theyproducedull sound when struck together.Theyare used for
temporaryand unimportant structures.
(IV)Fourth Class Bricks: These are the over burnt bricks. Theyare dark in color.The shapeis
irregular. Theyare used as aggregatesfor concrete in foundations, floors and roads
Properties of bricks
The following are the required properties of good bricks:
(I) Color: Color should be uniform and bright.
(ii) Shape: Bricks should have plane faces. They should have sharp and true right angled
corners.
(iii) Size: Bricks should be of standard sizes as prescribed by codes.
(iv) Texture: They should possess fine, dense and uniform texture. They should not possess
fissures, cavities, loose grit and unburnt lime.
(v) Soundness: When struck with hammer or with another brick, it should produce metallic
sound. (vi) Hardness: Finger scratching should not produce any impression on the brick. (vii)
Strength: Crushing strength of brick should not be less than 3.5 N/mm2. A field test for strength
is that when dropped from a height of 0.9 m to 1.0 mm on a hard ground, the brick should not
break into pieces.
(viii) Water Absorption: After immersing the brick in water for 24 hours, water absorption
should not be more than 20 per cent by weight. For class-I works this limit is 15 per cent.
(ix) Efflorescence: Bricks should not show white patches when soaked in water for 24 hours and
then allowed to dry in shade. White patches are due to the presence of sulphate of calcium,
magnesium and potassium. They keep the masonry permanently in damp and wet conditions.
(x) Thermal Conductivity: Bricks should have low thermal conductivity, so that buildings built
with them are cool in summer and warm in winter.
(xi) Sound Insulation: Heavier bricks are poor insulators of sound while light weight and
hollow bricks provide good sound insulation.
(xii) Fire Resistance:Fire resistance of bricks is usually good. In fact bricks are used to encase
steel columns to protect them from fire.

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Methods of manufacture.
Modern clay bricks are formed in one of three processes – soft mud, dry press, or extruded.
Normally, brick contains the following ingredients
 Silica (sand) – 50% to 60% by weight
 Alumina (clay) – 20% to 30% by weight
 Lime – 2 to 5% by weight
 Iron oxide – ≤ 7% by weight
 Magnesia – less than 1% by weight
 Mud bricks
 The soft mud method is the most common, as it is the most economical. It starts with
the raw clay, preferably in a mix with 25–30% sand to reduce shrinkage. The clay is
first ground and mixed with water to the desired consistency. The clay is then pressed
into steel moulds with a hydraulic press. The shaped clay is then fired ("burned") at
900–1000 °C to achieve strength.
 In modern brickworks, this is usually done in a continuously fired tunnel kiln, in
which the bricks are fired as they move slowly through the kiln on conveyors, rails, or
kiln cars, which achieves a more consistent brick product. The bricks often have lime,
ash, and organic matter added, which accelerates the burning process.
 Bull's Trench Kilns
 In India, brick making is typically a manual process. The most common type of brick
kiln in use there is the Bull's Trench Kiln (BTK), based on a design developed by
British engineer W. Bull in the late 19th century.
 An oval or circular trench is dug, 6–9 metres wide, 2-2.5 metres deep, and 100–150
metres in circumference. A tall exhaust chimney is constructed in the centre. Half or
more of the trench is filled with "green" (unfired) bricks which are stacked in an open
lattice pattern to allow airflow. The lattice is capped with a roofing layer of finished
brick.
.
 Dry pressed bricks
 The dry press method is similar to the soft mud brick method, but starts with a much
thicker clay mix, so it forms more accurate, sharper-edged bricks. The greater force in
pressing and the longer burn make this method more expensive.
 Extruded bricks
 For extruded bricks the clay is mixed with 10–15% water (stiff extrusion) or 20–25%
water (soft extrusion). This mixture is forced through a die to create a long cable of
material of the desired width and depth. This mass is then cut into bricks of the desired
length by a wall of wires. Most structural bricks are made by this method as it

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produces hard, dense bricks, and suitable dies can produce holes or other perforations
as well. The introduction of such holes reduces the volume of clay needed, and hence
the cost. Hollow bricks are lighter and easier to handle, and have different thermal
properties than solid bricks. The cut bricks are hardened by drying for 20 to 40 hours
at 50 to 150 °C before being fired. The heat for drying is often waste heat from the
kiln.
 European-style extruded bricks or blocks are used in single-wall construction with
finishes applied on the inside and outside. Their many voids comprise a greater
proportion of the volume than the solid, thin walls of fired clay. Such bricks are made
in 15-, 25-, 30-, 42- and 50-cm widths. Some models have very high thermal
insulation properties, making them suitable for zero-energy buildings.
 Influence on fired colour
 The fired colour of clay bricks is influenced by the chemical and mineral content of
the raw materials, the firing temperature, and the atmosphere in the kiln. For example,
pink colored bricks are the result of high iron content, white or yellow bricks have
higher lime content. Most bricks burn to various red hues; as the temperature is
increased the color moves through dark red, purple and then to brown or grey at
around 1,300 °C (2,372 °F). Calcium silicate bricks have a wider range of shades and
colors, depending on the colorants used. The names of bricks may reflect their origin
and color, such as London stock brick and Cambridge shire White.
 "Bricks" formed from concrete are usually termed blocks, and are typically pale grey
in color. They are made from a dry, small aggregate concrete which is formed in steel
moulds by vibration and compaction in either an "egg layer" or static machine. The
finished blocks are cured rather than fired using low-pressure steam. Concrete blocks
are manufactured in a much wider range of shapes and sizes than clay bricks and are
also available with a wider range of face treatments – a number of which simulate the
appearance of clay bricks.
 An impervious and ornamental surface may be laid on brick either by salt glazing, in
which salt is added during the burning process, or by the use of a "slip," which is a
glaze material into which the bricks are dipped. Subsequent reheating in the kiln fuses
the slip into a glazed surface integral with the brick base.
 Natural stone bricks are of limited modern utility due to their enormous comparative
mass, the consequent foundation needs, and the time-consuming and skilled labor
needed in their construction and laying. They are very durable and considered more
handsome than clay bricks by some. Only a few stones are suitable for bricks.
Common materials are granite, limestone and sandstone. Other stones may be used
(for example, marble, slate, quartzite, and so on) but these tend to be limited to a
particular locality.
 Optimal dimensions, characteristics, and strength

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For efficient handling and laying, bricks must be small enough and light enough to be
picked up by the bricklayer using one hand (leaving the other hand free for the trowel).
Bricks are usually laid flat and as a result the effective limit on the width of a brick is
set by the distance which can conveniently be spanned between the thumb and fingers
of one hand, normally about four inches (about 100 mm). In most cases, the length of a
brick is about twice its width, about eight inches (about 200 mm) or slightly more.
This allows bricks to be laid bonded in a structure which increases stability and
strength (for an example, see the illustration of bricks laid in English bond, at the head
of this article). The wall is built using alternating courses of stretchers, bricks laid
longways, and headers, bricks laid crossways. The headers tie the wall together over
its width. In fact, this wall is built in a variation of English bond called English cross
bond where the successive layers of stretchers are displaced horizontally from each
other by half a brick length. In true English bond the perpendicular lines of the
stretcher courses are in line with each other.
 A bigger brick makes for a thicker (and thus more insulating) wall. Historically, this
meant that bigger bricks were necessary in colder climates (see for instance the
slightly larger size of the Russian brick in table below), while a smaller brick was
adequate, and more economical, in warmer regions. A notable illustration of this
correlation is the Green Gate in Gdansk; built in 1571 of imported Dutch brick, too
small for the colder climate of Gdansk, it was notorious for being a chilly and drafty
residence. Nowadays this is no longer an issue, as modern walls typically incorporate
specialized insulation materials.
 The correct brick for a job can be selected from a choice of colour, surface texture,
density, weight, absorption and pore structure, thermal characteristics, thermal and
moisture movement, and fire resistance.
Different Forms of Bricks
Bricks may be broadly classified as:
(I) Building bricks
(ii) Paving bricks
(iii) Fire bricks
(iv) Special bricks.
(i) Building Bricks: These bricks are used for the construction of walls.

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(ii) Paving Bricks: These are vitrified bricks and are used as pavers.
(iii) Fire Bricks: These bricks are specially made to withstand furnace temperature. Silica bricks
belong to this category.
(iv) Special Bricks: These bricks are different from the commonly used building bricks with
respect to their shape and the purpose for which they are made. Some of such bricks are listed
below:
(a) Specially shaped bricks
(b) Facing bricks
(c) Perforated building bricks
(d) Burnt clay hollow bricks
(e) Sewer bricks
( f ) Acid resistant bricks.
(a) Specially Shaped Bricks: Bricks of special shapes are manufactured to meet the
requirements of different situations. Some of them are shown in
Fig. (b) Facing Bricks: These bricks
are used in the outer face of masonry. Once these bricks are provided, plastering is not required.
The standard size of these bricks are 190 × 90 × 90 mm or 190 × 90 × 40 mm.
(c) Perforated Building Bricks: These bricks are manufactured with area of perforation of 30 to
45 per cent. The area of each perforation should not exceed 500 mm2. The perforation should be
uniformly distributed over the surface. They are manufactured in the size 190 × 190 × 90 mm
and 290 × 90 × 90 mm.
(d) Burn’t Clay Hollow Bricks: Figure shows a burnt clay hollow brick. They are light in
weight. They are used for the construction of partition walls. They provide good
thermal insulation to buildings. They are manufactured in the sizes 190 × 190 × 90 mm, 290 × 90

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× 90 mm and 290 × 140 × 90 mm. The thickness of any shell should not be less than 11 mm and
that of any web not less than 8 mm.
(e) Sewer Bricks: These bricks are used for the construction of sewage lines. They
are manufactured from surface clay, fire clay shale or with the combination of these. They are
manufactured in the sizes 190 × 90 × 90 mm and 190 × 90 × 40 mm. The average strength of
these bricks should be a minimum of 17.5 N/mm2 . The water absorption should not be more
than 10 per cent.
( f ) Acid Resistant Bricks: These bricks are used for floorings likely to be subjected to
acid attacks, lining of chambers in chemical plants, lining of sewers carrying industrial
wastes etc. These bricks are made of clay or shale of suitable composition with low lime and iron
content, flint or sand and vitrified at high temperature in a ceramic kiln.
Test Of Bricks
The following laboratory tests may be conducted on the bricks to find their suitability:
(i) Crushing strength
(ii) Absorption
(iii) Shape and size and
(iv) Efflorescence.
(i) Crushing 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

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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.
(ii) Absorption Test: Brick specimen are weighed dry. Then they are immersed in water for
a period of 24 hours. The specimen are taken out and wiped with cloth. The weight of each
specimen in wet condition is determined. The difference in weight indicate the water absorbed.
Then the percentage absorption is the ratio of water absorbed to dry weight multiplied by 100.
The average of five specimen is taken. This value should not exceed 20 per cent. sharp edges. To
check it, 20 bricks are selected at random and they are stacked along the length, along the width
and then along the height. For the standard bricks of size 190 mm × 90 mm × 90 mm. IS code
permits the following limits: Lengthwise: 3680 to 3920 mm Widthwise: 1740 to 1860 mm
Heightwise: 1740 to 1860 mm. The following field tests help in acertaining the good quality
bricks:
(i) uniformity in size
(ii) uniformity in colour
(iii) structure
(iv) hardness test
(v) sound test
(vi) strength test.
(i) Uniformity in Size: A good brick should have rectangular plane surface and uniform in size.
This check is made in the field by observation. (ii) Uniformity in Colour: A good brick will be
having uniform colour throughout. This observation may be made before purchasing the brick.
(iii) Structure: A few bricks may be broken in the field and their cross-section observed. The
section should be homogeneous, compact and free from defects such as holes and lumps.
(iv) Sound Test: If two bricks are struck with each other they should produce clear ringing
sound. The sound should not be dull.
(v) Hardness Test: For this a simple field test is scratch the brick with nail. If no impression is
marked on the surface, the brick is sufficiently hard
(vi) Efflorescense: The presence of alkalies in brick is not desirable because they form patches
of gray powder by absorbing moisture. Hence to determine the presence of alkalies this test is
performed as explained below: 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 to mean
(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.

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THE END