bricks

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FIRED CLAY PRODUCTS

• BRICKS

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Outline

• 1. Definition
• 2. Advantages and disadvantages of bricks
• 3. Bricks raw material clay chemical elements
• 4. Process of manufacturing of bricks
• 5. Types and classification of bricks
• 6. Properties of bricks
• 7. Tests for clay bricks

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General

• A clay brick is a small solid block ,usually
  rectangular, made of burned clay.
• The word brick comes from the French word
  brique.
• The technique of firing clay to produce bricks
  and tiles for building construction is more than
  4000 years old.
• The art of brick making have spread from Egypt to
  Greece and then to Rome.

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ADVANTAGES OF FIRED CLAY PRODUCTS

• Fired clay products
• Can have high compressive strengths
• Provide excellent fire-resistance
• Weather resistant and can remain without any
  surface protection
• Have no wastage

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DISADVANTAGES OF FIRED CLAY PRODUCTS

• Relatively high fuel consumption of the firing
  process
• A possible defect of burnt bricks"efflorescence"
• Good quality fired clay products tend to be
  expensive
• Capital investments for fuel efficient kilns are
  often too high

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Suitability of bricks

• At present, bricks are the most favored
  construction material worldwide due to the
  following reasons
• Availability-clays are available almost
  universally.
• Construction methods-very experienced skill
  bricklayers are available in all villages, towns
  
• Size, shape and handling-Bricks are made in
  ready-to-use sizes and shapes

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RAW MATERIALS

• Bricks are manufactured from clays.
• By moistening and mixing with water, clays
  become plastic, easy to mould and are capable to
  retain their shape on drying.
• Clay soils are of two types
• Residual clay (Formed from decay of underlying
  rocks)
• Transported clay/sedimentary(formed from
  materials removed from parent rock ,transported
  and deposited somewhere else by wind or air.

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FUNCTIONS OF THE CONSTITUENT OF CLAY

• Clays generally consist of the following
  chemical elements
• Alumina- (Al2O3)
• Silica (SiO2)
• Lime - (CaO)
• Iron oxide - (Fe2O3)
• Magnesia (MgO)

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Alumina- (Al2O3)

• Makes the major part of clay
• Responsible for plasticity of the mud
• When burnt, alumina becomes stronger and harder.
• Excess alumina content? brick will shrink on
  drying? cracking and warping.
• Small alumina content? the brick will not be
  molded easily.

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Silica (SiO2)

• Reduce shrinkage and warping in burning
• Responsible for strength, hardness and durability
  or long life
• A large percentage of uncombined silica is
  undesirable because it leads to brittleness of
  the product

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Lime - (CaO)

• Acts as a binder to the clay and silica particles
  leading to greater strength
• Acts as flux and lower the fusion point of
  silica.
• Excess lime case the brick to melt and lose the
  shape.

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Iron oxide - (Fe2O3)

• Imparts the colors of the clay and the burnt
  product
• Acts as a flux i.e. it lowers down the softening
  temperature of silica
• Excess iron oxide ? the brick becomes too soft
  during burning ? dark in appearance.
• Small iron oxide content --If it is small in
  quantity than required it affects the color of
  the brick, instead of being brick red, they may
  be yellow.

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Magnesia (MgO)

• Gives the brick darker or even black color
• Minimizes warping of bricks in burning
• Magnesia is present in small quantity (1)

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MANUFACTURE OF BRICKS

• The process of manufacture of bricks is
  carried out in a number of stages.
• Selection of suitable type of brick earth
• Preparations and tempering of mud
• Shaping and molding of brick units
• Drying of molded bricks
• Firing or burning of units
• Cooling of the units

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1. Selection of suitable type of brick earth

• A clay soil for brick making should be such
  that when prepared with water, it can be molded,
  dried and burnt without cracking or changing its
  shape or warping.
• The ideal composition of a good brick earth is
• Clay (Alumina) 20-30
• Silica (free and combined) 50-60
• CaO, MgO 4.5
• Iron oxide 4-6
• The earth should be free from alkalis, organic
  matter and free lime.

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2. Preparation and tempering of mud

• A two stage process
• Clay Wining The operations of selecting the
  earth, clearing and digging it, spreading it for
  weathering.
• Tempering the process of converting the prepared
  brick earth into a homogeneous mix of desired
  plasticity by mixing it thoroughly with proper
  quantities of water.

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3. Shaping and Molding of bricks

• Molding is the process of making properly shaped
  brick units from thoroughly tampered clay.
• The brick at this stage is known as green
  brick.

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4. Drying of bricks

• After molding, the green bricks have to be
  dried.
• Reasons for drying
• To make them sufficiently rigid, strong for
  handling and stacking
• To minimize the risk of rapture
• To save fuel during burning stage
• Drying of bricks is achieved either by natural
  methods or by artificial methods.

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Drying of bricks by natural methods
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5. Firing

• Firing of the dried bricks is essential to
  develop the desired building properties such as
• Sufficient strength
• Hardness
• Durability and
• Resistance to decay and disintegration

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THE FIRING PROCESS

1. Temperature (20-150oc)loss of moisture.
2. Temperature (150-600oc)loss of moisture,
   hardening starts.
3. Temperature (600-950oc)chemical changes start to
   occur which gives the brick color ,hardness
   durability.
4. Temperature (950-1200oc)verification occurs
   (glass like material forms which glue all of the
   elements together.)

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Methods of burning

• There are two types of firing kilns for bricks
  
• intermittent and
• continuous kilns
• At present, there are two main methods of
  burning of bricks in developing countries
• Clamp burning
• Kiln burning

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The two main methods of burning
Clamp burning
Kiln burning
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Effects of improper burning

• Over or under sized bricks
• (due to difference in temp types of clay )
• 2. Glazed bricks
• (over burning)
• 3. Low strength bricks
• (poor quality clay, improper burning)
• 4. Cracked or broken bricks
• (opening the kiln before cooling, burning before
  drying)

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TYPES AND CLASSIFICATION OF BRICKS

• Bricks can be classified according to their
  usage as
• Common bricks and
• Facing Bricks

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1. Common Bricks

• Common bricks are those that are used where they
  will not normally be exposed to view and where
  there is no claim as to their appearance.
• They are suitable for general use in
  construction, given that they possess adequate
  strength and durability for the location.

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2. Facing Bricks

• Facing bricks have a suitable appearance for use
  where they will be exposed to view so that they
  give an attractive and pleasant effect.

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Solid and hollow clay bricks

• Bricks can be classified according to their
  shape and nature as
• Solid clay bricks and
• Hollow clay bricks

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Solid Clay Bricks

• According to the Ethiopian Standard, solid
  bricks are of the following three types.
• Brick without holes or depression (type TS)
• Brick with holes up to 20 mm in diameter each and
  having a total cross sectional area not exceeding
  25 of the base area of the brick (type TH)
• Brick with depression not exceeding 25 percent of
  the base area having a maximum depth of the
  depression not more than 10mm (type TD).

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Hollow Clay Bricks

• According to the Ethiopian Standard, hollow
  and beam tiles bricks are of the following three
  types.
• With two faces keyed for plastering or rendering
  (type kk)
• With two faces smooth and suitable for use with
  out plastering or rendering on either side.(type
  ss) and
• With one face smooth and another face keyed for
  plastering (type sk)

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Firebricks or Refractory bricks

• These bricks are capable of withstanding very
  high temperatures without melting or becoming
  soft.
• Firebricks are manufactured in exactly the same
  manner as the ordinary bricks burnt in kilns at
  temperatures ranging from 13500c to 19000c.
• Firebricks are the white or yellowish white color
  and are used for lining the interiors of
  fireplaces, ovens, kilns, chimneys and furnaces

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Properties of Bricks

• The essential properties of bricks are
• Physical properties,
• Chemical characteristics,
• Thermal characteristics and
• Durability.

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1.Physical properties

• a. Shape- rectangular
• b. Size 60 mmx120mmx250mm
• c. Color red
• d. Density- density varies from 1600 kg/cubic
  meter to 1900 kg/cubic meter. A single bricks
  (60x120x250) will weigh between 3.2kg to 3.5kg
  depending upon its density.

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2. Mechanical properties

• Compressive strength 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 the clay and degree of
  burning.
•  

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3.Thermal properties

• The heat and sound conductivity of bricks
  varies greatly with their density and porosity.
• Very dense and heavy bricks conduct heat and
  sound at a great rate.
• They have therefore poor thermal and acoustic
  (sound) insulation qualities. For this reason,
  bricks should be so designed that they are light
  and strong and give adequate insulation.

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4. Durability

• By durability of bricks is understood the
  length of time for which they remain unaltered
  and strong when used in construction.
• The durability of bricks depends on a number
  of factors such as
• absorption value,
• frost resistance and efflorescence.

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Tests for Clay Bricks

• Two types of tests are used to determine the
  quality of building bricks.
•   A.   Field test
• B. Laboratory test

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A) Field tests

• such as appearance, hammer and hardness  
• Appearance test is that shape, plainness, color
  etc.
• When stroked with hammer, a properly burnt dry
  brick free from cracks emits a highly metallic
  ring.
• The hardness of a brick sample can be checked by
  scratching its surface or broken section with a
  knife or fingernail. A well-burnt brick will be
  scratched with difficulty.
• A rough test for the strength of the brick is to
  let it fall freely from a height of about one
  meter on to a hard floor. It should not break.

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B) Laboratory tests

• 1. Compressive strength test
• 2. Water absorption test
• 3. Efflorescence test and
• 4. Saturation coefficient test
• (absorption after 24
  hrs in cold water)
• 
  absorption after boiling for 5hrs

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Minimum Compressive Strength
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2. Maximum water absorption. () Table 2
Maximum water absorption
Class   After 24hr.lmmersion After 24hr.lmmersion After 5hr.Boiling After 5hr.Boiling
Class   Average of 5 bricks Individual bricks Average of 5 bricks Individual bricks
A 21 23 22 24
B 22 24 23 24
C,D No Limit No Limit No Limit No Limit
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3. Maximum Saturation Coefficient Table 3
Maximum Saturation coefficients
Class Average of 5 bricks Individual bricks
A,B 0.96 0.99
C,D No Limit No Limit
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4. Efflorescence Rating Table 4 Efflorescence
Rating
Class Efflorescence
A,B Nil to slight
C,D Effloresced
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Qualities of good brick

• 1. It should have a regular shape, surface and
  red colored appearance.
• 2. It should confirm in size to the specific
  dimensions (60mmx120mmx250mm)
• 3.    It should be properly burnt.
• 4.  Absorption should not exceed 25 in any case.
• 5. A good building brick should posses requisite
  compressive strength, which in no case should be
  less than 35kg/cm2.
• 6. Bricks should be hard enough so that it is not
  scratched by fingernail.
• 7. A good brick has a uniform color and structure
  through its body.

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• The End