12 - Ms.Mukta Banu PDF

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Ms.Mukta Banu...

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Chittagong University of Engineering & Technology Department of Urban & Regional Planning

CE 209 Construction Materials Sanjoy Das Lecturer Department of Civil Engineering

BRICK

Definit ion  A Brick is an artificial kind of stone made of clay w hose chief characteristics are a plasticity w hen w et & stone like hardness after being heated to high temperature.

BRICKS  It is a regular sized rectangular

unit  Used for most of the building works  Used as substitute for stone, where stone is not available

Ingredients of Good Brick Earth  A good br ick ear th mainly consists of silica

(sand) and alumina (clay)

Ingredients of Good Brick Earth • • • • • •

Alumina (Clay)(Aluminum Oxide) Silica (Sand) Lime Iron Oxide Magnesia(Magnesium Oxide) Alkalies & Organic Matter

Ingredients of Good Brick Earth The ingredients are mixed in such a proportion that The resulting mass with water is a plastic mass

Can be easily moulded and dried

without undergoing shrinkage, cracking or warping

Ingredients of Good Brick Earth Alumina (Clay)  Alumina is the chief constituent of every kind of clay  A good brick earth should contain 20 to 30 % of alumina  Provides plasticity to earth, so that it can be moulded  If bricks contain excess amount of alumina and insufficient sand, they shrink, crack and warp on drying and burning

Ingredients of Good Brick Earth Silica (Sand)  Good brick earth should contain 50 to 60 %  Presence of silica prevents cracking, shrinking and warping of raw bricks  Excess amount of silica destroys the cohesion between particles and makes the bricks brittle and weak  Hence, durability of the bricks depends largely on the proper proportion of silica & alumina in brick earth

Ingredients of Good Brick Earth Lime  Small quantity(1%) of lime in brick earth is desirable  Slight amount of lime in a very finely powdered form acts as a flux and causes silica to fuse slightly at kiln temperature  Such slightly fused sand acts as a very hard cementing material and bricks of large strength and durability are obtained  Lime present in small proportion also prevents shrinkage of raw bricks  Excess amount of lime causes the brick to melt and its shape is lost

Ingredients of Good Brick Earth Oxide of Iron  About 5 to 6 % is desirable in good brick earth  It also helps silica to fuse at comperatively low temperature like lime  The color of bricks depends on the proportion of iron oxide present in the brick earth  The bricks having very small amount of iron oxide are yellow in color  Iron also increases the durability and impermeability of the bricks

Ingredients of Good Brick Earth Magnesia  A small proportion(5%) of it decreases the

shrinkage and gives yellow tint to the bricks  Excess amount of magnesia causes bricks to

decay

Ingredients of Good Brick Earth Alkalies & Organic Matter  A small quantity of organic matter assist

burning the bricks.  Small quantity of Alkalies lower the fusion

point of clay.

Proportion of the Ingredients of Typical Good Brick Earth Ingredients

Percentage

Alumina

20-30 %

Silica

50-60 %

Lime & Magnesia

6-10 %

Iron Oxide

4-8%

Organic Matter

3-6 %

Harmful Ingredients of Brick Earth Harmful Ingredients of Brick Earth • • • • • •

Lime Pebbles of Stone & Gravel Iron Pyr ites Alkalies Or ganic Matter Presence of Vegetation

Harmful Ingredients of Brick Earth Lime  Presence of lime in large amount is harmful  Calcium Carbonate present in lumps is converted to quick lime (CaO) after burning of bricks  When these bricks come into contact with moisture, quick lime slakes and causes disruption of bricks because of its expansion  Excess amount of lime also causes the brick to melt and its shape is lost

Harmful Ingredients of Brick Earth Pebbles of Stone and Gravel  Do not allow thorough mixing of the earth  Bricks containing pebbles and gravels are

considered very week  Such bricks cannot be broken at the desired section and they break very irregularly

Harmful Ingredients of Brick Earth Iron Pyrites  Presence of iron pyrites causes crystallization

and disintegration of bricks during burning  It causes discoloration of bricks in the form of black slag

Harmful Ingredients of Brick Earth Alkalies  Mainly salts of sodium and potassium  Act as flux in the kiln and cause fusion, warping and twisting of the bricks  Alkalies present in bricks absorb moisture from the atmosphere  Such bricks when used for masonry work cause deposition of white powder on the surface. Because when drying; the salts, which have come to the surface with moisture, get deposited  This action is known as efflorescence, which seriously spoils the appearance of the building

Harmful Ingredients of Brick Earth Organic Matter  Presence of organic matter and vegetation

in the brick earth render the bricks porous

Broad Classification of Bricks Classification of Bricks Fir st Class Br icks Second Class Br icks Third Class Br icks Over Bur nt or Jhama Br icks Under Bur nt or Pilla br icks Fir st & Second Class Bats Jhama Bats

First Class Bricks

(S-grade,BDS 208:2002)

Properties  Size of the burnt brick is exactly 9.5”x4.5”x2.75”  The brick earth is free from small pebbles, lime lumps, organic matter and sodium salts  Well burnt  Color is uniform yellow or red  Surface is regular and sides are parallel, edges are sharp and at right angles to each other  Have firm, compact and uniform texture  No sign of efflorescence

First Class Bricks

(S-grade,BDS 208:2002)

Properties  Crushing strength more than 280 kg/cm2 (mean value) and 245 kg/cm2 (individual minimum value)  Surface is so hard that finger nails are not able to make any impression on its surface  Does not absorb water more than 10 % of its own dry weight  Metallic ringing sound emits when two bricks are struck against each other  Does not break when it is dropped on a hard ground from a height of 1 meter

First Class Bricks

(S-grade,BDS 208:2002)

Uses  Used in all works of long durability, say

100 years  Used for buildings that expose to corrosive environment  Used as coarse aggregate of concrete

Second Class Bricks

(A-grade,BDS 208:2002)

Properties  Well burnt or slightly over burnt  Color is uniform yellow or red  Generally regular and uniform shape, size and

color  Uniform texture  No appreciable sign of efflorescence

Second Class Bricks

(A-grade,BDS 208:2002)

Properties  Ringing sound emits when two bricks are struck

against each other  Does not absorb water more than 15 % of its own dry weight after immersion of 24 hours in cold water  Crushing strength more than 175 kg/cm2 (mean value) and 154 kg/cm2 (individual minimum value)  No finger nail impression

Second Class Bricks

(A-grade,BDS 208:2002)

Uses  Used in less important structures  Used for general purposes

Third Class Bricks

(B-grade,BDS 208:2002)

Properties  Generally under burnt  Soft and light red colored  Size and shape are not regular  Intensive efflorescence  Texture is not uniform  Emit a dull sound when struck against each

other

Third Class Bricks

(B-grade,BDS 208:2002)

Properties  Does not absorb water more than 20 % of

its own dry weight after immersion of 24 hours in cold water  Crushing strength more than 140 kg/cm2 (mean value) and 105 kg/cm2 (individual minimum value)  Leave finger nail impression

Third Class Bricks

(B-grade,BDS 208:2002)

Uses  Not used for important and permanent

works  Mostly used for temporary works

Over Burnt or Jhama Bricks Properties  Over burnt  Shape vitrified and distorted Uses  Can not be used in construction works  Used for making aggregate for lime concrete for foundation  As a road material

Under Burnt or Pilla Bricks Properties  Half burnt  Yellow color  Low strength Uses  Crushed to powder form and used as surkhi

Manufacture of Bricks Manufacture of Bricks Preparation of Clay Pugging or Tempering of the Clay Moulding of Bricks

Drying of Bricks

Burning of Bricks

Manufacture of Bricks Preparation of Clay or Earth  Preparation

of clay involves operations like removing the top loose earth, then digging, cleaning, weathering and blending of the earth  After removing the top unsuitable soil, the clay is dug either by manual labor or by power excavators  Dug out clay is spread out on the leveled ground and all the pebbles, gravel, kankar, vegetable matter etc. are removed from the clay

Manufacture of Bricks

Preparation of Clay or Earth  The clay is left exposed to atmosphere for softening, known as weathering of clay.  This process has an important effect on the plasticity & strength of the clays.  The clay should be kept moist during the period it is weathered.  Digging the earth before rains is advantageous as full monsoon can be utilized for weathering  After weathering, the earth is chemically analyzed and if there is any deficiency of any ingredient, it is mixed with the earth  The quality of brick clay is to be improved (if there is any deficit of important constituent ingredients) by adding sand, lime, alumina, magnesia etc.. This process is known blending.  Now preparation of clay is completed

Manufacture of Bricks Pugging or Tempering of Clay  The clay is then cut slashed & well worked with spade & is trodden which makes it soft. This process is known as tempering.  Tempering or pugging of clay involves breaking up of the prepared clay, watering and kneading till the earth becomes a homogeneous mass having uniform consistency. So that it may posses the required plasticity for molding .  Water is added to clay in required quantity and the whole mass is kneaded under the feet of men or cattle  Where good bricks are required to be manufactured on a large scale, tempering of clay is usually done by pugmill

Manufacture of Bricks

Moulding of Bricks  After tempering of clay, bricks should be moulded as soon as possible; otherwise pugged clay may become stiff and moulding of bricks may become difficult  The bricks can be moulded by  Hand moulding  Machine moulding  Moulds are rectangular boxes without any top and bottom. They may be made of steel or timber  The internal dimensions of the mold about 1/10 larger than the size of the burnt bricks to allow for shrinkage on burning.  Generally identification marks (Frogs & impression) are left on the face of the brick during the process of molding to indicate the name of the manufacturer of bricks.

Manufacture of Bricks Drying of Bricks  Wet bricks have to be dried before they are fed for burning in the kilns. The objectives of drying the bricks are  To remove as much of moisture from the bricks as

possible, so as to save time and fuel during the burning  To avoid the chances of cracking and distortion of bricks during the burning  To increase the mechanical strength of the bricks, so that they can be handled and stocked without any damage to the bricks  Brick drying generally takes 5 to 12 days depending upon the local climate conditions.

Manufacture of Bricks Burning of Bricks  Burning of bricks is a very important operation in the manufacturing of bricks  It imparts strength and hardness to the bricks and makes them dense and durable  When temperature of bricks reaches at 650°C, while burning, water of crystallization is removed  At that temperature , the organic matter present in the bricks is oxidized & disappears.  At about 1149° C, the two main constituents of brick, silica and alumina, combine with each other and bricks become dense and strong  Bricks are burnt either in clamps or in kilns

Kilns The kiln is a system, designed more scientifically, to burn the bricks in very large numbers

Type of Kilns

Inter mittent kiln

Continuous kiln

Kilns Intermittent Kiln  Operation of burning the bricks is not continuous  The kiln is loaded, then fired, then allowed to cool and lastly unloaded Loading Start of Cycle Firing

End of One Cycle

Cooling Unloading

Kilns Disadvantages of Intermittent Kiln  Supply of bricks is intermittent  Quality of burnt bricks is not uniform. Bricks

near bottom are over burnt and those near top are under burnt  There is wastage of fuel as kiln is to be cooled down every time after burning

Kilns Continuous Kiln  Continuous in operation and ensures continuous supply of burnt bricks  All operations like loading, firing, cooling and unloading are carried out simultaneously in these kilns Bull’s Trench Kiln Mostly Used Continuous Kiln

Hoffman’s Kiln

Tunnel Kiln

Hoffman’s Kiln  This kiln is circular in plan  The chimney is placed at the centre and twelve

 

 

chambers are arranged around the chimney forming a circular ring Each chamber has a door in the external wall which is used for loading and unloading of bricks All the chambers have communicating doors in the walls separating each other and all the chambers have a connection with chimney with radial flues The kiln has permanent roof but fuel holes are provided to drop the fuel in the kiln from top In this kiln, all the chambers are subjected to loading, drying and pre-heating, burning, cooling and unloading operations successively and all these operations remain going on all the time simultaneously

Hoffman’s Kiln

Hoffman’s Kiln All the twelve chambers of the kiln may be functioning as follows Chamber No.

Operation Involved

1

Loading

2, 3, 4, 5

Dr ying & Pre-heating

6, 7

Bur ning

8, 9, 10, 11

Cooling

12

Unloading

Hoffman’s Kiln The circulation of flue gas with this arrangement  Cool air enters the kiln through open doors of chambers

1 and 12  This cool air passes through chambers 11, 10, 9, and 8 and in course of time gets heated, while performing cooling of the hot-burnt bricks in these chambers  Now this heated air or gas enter the burning chambers 7 and 6, where it performs the burning of bricks. Fuel is dropped in these chambers from the top  After performing burning of bricks, hot gas is led to chambers 5, 4, 3 and 2 where they perform drying and pre-heating of freshly loaded bricks

Hoffman’s Kiln The circulation of flue gas with this arrangement  The communicating door of chamber 2 is closed and

cooled gas is led to chimney through the radial flue of this chamber  Care should be taken that all radial flues except of chamber 2 remain closed and all communicating doors except in the wall between chambers 1 and 2 remain open for this particular arrangement. Outer loading and unloading doors remain closed except for the two chambers, which are being loaded and unloaded

Hoffman’s Kiln After the burning of bricks of chamber 7 and 6, the pattern of circulation will be as follows Chamber No.

Operation Involved

12

Loading

1, 2, 3, 4

Dr ying & Pr e-heating

5, 6

Bur ning

7, 8, 9, 10

Cooling

11

Unloading

Hoffman’s Kiln Advantages  There is perfect control on the heat  Supply of bricks is continuous and regular  Pre-heating of the bricks by hot gases before they

escape into the atmosphere, considerably reduce the consumption of the fuel  Preheating of un-burnt bricks  Bricks are burnt evenly and thus bricks of good quality are produced  Percentage of first class bricks is the highest

Hoffman’s Kiln Disadvantages  Initial cost of construction is high  This kiln requires regular demand of the bricks

which may not be possible

Desirable Characteristics of Good Bricks  The color of good brick should be uniform. It may  

 

be deep red or yellow Bricks should be uniform in shape with all its edges sharp, straight and at right angles to each other Size of the bricks should be standard (24cm x 11.5cm x 7cm) as prescribed by Bangladesh Standards (BDS, 2002) The bricks should have fine, dense, compact and uniform texture First class bricks should not absorb water more than 10 % of its own dry weight after immersion of 24 hours in cold water

Desirable Characteristics of Good Bricks  Crushing strength more than 280 kg/cm2 (mean



  

value) and 245 kg/cm2 (individual minimum value) (BDS, 2002) The bricks should be so hard that finger nails should not be able to make any impression on its surface when scratched Two bricks when struck against each other should emit metallic sound Bricks should be sound proof and also of low thermal conductivity Bricks should not break when dropped flat on a hard ground from a height of 2 (~6 ft)meter or the nose level.

Tests for Bricks

 Absorption capacity Test  Crushing Strength Test  Unit weight test  Hardness Test  Shape and Size Test  Soundness Test  Test for Presence of Soluble Salts

Coloring of Bricks Factors Affecting the Color Bur ning temperatur e of br icks Type of fuel used dur ing bur ning Chemical composition of the br ick ear th Natur e of sand used dur ing molding Degr ee of dr yness achieved befor e bur ning Amount of air admitted to the kiln dur ing bur ning

The color attained by any of the above causes is known as the natural color of the brick

Coloring of Bricks  Bricks can be colored artificially also  By

dipping (immersing in coloring mixture)  By mixing appropriate coloring material during preparation of brick earth/clay

Fire Bricks or Refractory Bricks  These bricks are manufactured from specially

designed earth, so that after burning, they can withstand very high temperatures without affecting its shape, size and strength  They are used for lining of chimneys, furnaces

etc., where usual temperatures are expected to be very high

Special Bricks  Perforated bricks  Hollow bricks  Checkered Bricks  Stalle Bricks  Plinth Bricks  Jamb Bricks  Klinker (Paving) Bricks  Holed bricks

Uses of Bricks  Construction of walls of any size  Construction of floors  Construction of arches & cornices  Making khoa (broken bricks of required size) to use as an aggregate in concrete  Manufacture of surki (powdered bricks) to be used in lime plaster & lime concrete....