Effects of Silica, Alumina, and Lime on Brick Clay
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Questions and Answers

Excess of silica makes the brick ______ and weak on burning.

brittle

If alumina is present in excess of the specified quantity, it produces ______ in brick on drying.

cracks

Lime normally constitutes less than 10 per cent of ______.

clay

Lime in brick clay has the effect of reducing the ______ on drying.

<p>shrinkage</p> Signup and view all the answers

Excess of lime causes the brick to ______ and the brick loses its shape.

<p>melt</p> Signup and view all the answers

Magnesia rarely exceeding 1 percent affects the ______ and makes the brick yellow.

<p>colour</p> Signup and view all the answers

Iron oxide constituting less than 7 percent of clay, imparts ______ colour on burning when excess of oxygen is available.

<p>red</p> Signup and view all the answers

Improved kiln designs and more advanced ______ have all contributed to advancing the brick industry.

<p>mechanization</p> Signup and view all the answers

Clay is one of the most abundant natural ______ materials on earth.

<p>mineral</p> Signup and view all the answers

After pugging, the tempered clay goes through a de airing chamber that maintains a vacuum of 15 to 29 in.(375 to 725 mm) of ______.

<p>mercury</p> Signup and view all the answers

The soft-mud or molded process is particularly suitable for clays containing too much ______ to be extruded by the stiff-mud process.

<p>water</p> Signup and view all the answers

Clays are mixed to contain 20 to 30 percent ______ and then formed into brick in molds.

<p>water</p> Signup and view all the answers

To prevent clay from sticking, the molds are lubricated with either ______ or water to produce “sand-struck” or “water-struck” brick.

<p>sand</p> Signup and view all the answers

This process is particularly suited to clays of very low ______.

<p>plasticity</p> Signup and view all the answers

Clay is mixed with a minimal amount of ______ (up to 10 percent), then pressed into steel molds under pressures.

<p>water</p> Signup and view all the answers

Wet brick from molding or cutting machines contain 7 to 30 percent ______, depending upon the forming method.

<p>moisture</p> Signup and view all the answers

The brick are typically placed by ______ or mechanical means.

<p>robots</p> Signup and view all the answers

Fuel may be ______ gas, coal, sawdust, methane gas from landfills or a combination of these fuels.

<p>natural</p> Signup and view all the answers

The manufacturing process has six general phases, including _______________ of raw materials.

<p>mining and storage</p> Signup and view all the answers

Surface clays, shales and some fire clays are mined in open pits with _______________ equipment.

<p>power</p> Signup and view all the answers

To break up large clay lumps and stones, the material is processed through _______________ machines.

<p>size reduction</p> Signup and view all the answers

The material is processed through _______________ vibrating screens to control particle size.

<p>inclined</p> Signup and view all the answers

Tempering produces a _______________, plastic clay mass.

<p>homogeneous</p> Signup and view all the answers

Water is added to the clay in a _______________ to achieve tempering.

<p>pug mill</p> Signup and view all the answers

There are three principal processes for forming brick: _______________-mud, soft-mud and dry-press.

<p>stiff</p> Signup and view all the answers

In the stiff-mud or extrusion process, water in the range of 10 to 15 percent is mixed into the clay to produce _______________.

<p>plasticity</p> Signup and view all the answers

The final phase of the manufacturing process is _______________ and storing finished products.

<p>de-hacking</p> Signup and view all the answers

In a tunnel kiln, bricks are loaded onto ______ cars, which pass through various temperature zones as they travel through the tunnel.

<p>kiln</p> Signup and view all the answers

Firing may be divided into five general stages: 1) final drying (evaporating free water); 2) dehydration; 3) oxidation; 4) ______; and 5) flashing or reduction firing.

<p>vitrification</p> Signup and view all the answers

Although the actual temperatures will differ with ______ or shale, final drying takes place at temperatures up to about 204 ºC.

<p>clay</p> Signup and view all the answers

De-hacking is the process of unloading a ______ or kiln car after the brick have cooled, a job often performed by robots or machines.

<p>kiln</p> Signup and view all the answers

When a desirable amount of lime is present in the ______, it results in good bricks, but if in excess, it changes the colour of the brick from red to yellow.

<p>clay</p> Signup and view all the answers

Pebbles, Gravels, Grits : do not allow the ______ to be mixed thoroughly and spoil the appearance of the brick.

<p>clay</p> Signup and view all the answers

On burning green bricks, the organic matter gets charred and leave pores making the bricks ______; the water absorption is increased and the strength is reduced.

<p>porous</p> Signup and view all the answers

Alkalis (Alkaline Salts) : forming less than 10 per cent of the raw ______, are of great value as fluxes, especially when combined with silicates of alumina.

<p>clay</p> Signup and view all the answers

Cooling is an important stage in brick manufacturing because the rate of cooling has a direct effect on ______.

<p>color</p> Signup and view all the answers

When bricks come in contact with ______, water is absorbed and the alkalis crystallise.

<p>moisture</p> Signup and view all the answers

On drying, the ______ evaporates, leaving behind grey or white powder deposits on the brick.

<p>moisture</p> Signup and view all the answers

Efflorescence should always be ______ brushed away before rendering or plastering a wall.

<p>dry</p> Signup and view all the answers

Sulphur is usually found in clay as the sulphate of ______, magnesium, sodium, potassium or iron.

<p>calcium</p> Signup and view all the answers

If there is ______ 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.

<p>carbon</p> Signup and view all the answers

A large proportion of ______ water generally causes clay to shrink considerably during drying.

<p>free</p> Signup and view all the answers

The use of water containing small quantities of magnesium or calcium carbonates, together with a ______ fuel often causes similar effects as those by sulphur.

<p>sulphurous</p> Signup and view all the answers

The brick will be decoloured by white ______ if there is carbon in the clay and insufficient time is given during burning for proper oxidation of carbon and sulphur.

<p>blotches</p> Signup and view all the answers

Efflorescence is a phenomenon that spoils the ______ of the brick.

<p>appearance</p> Signup and view all the answers

Study Notes

Chemical Composition of Clay

  • Excess silica in clay makes bricks brittle and weak on burning
  • Alumina (Al2O3) absorbs water and makes clay plastic, but excess alumina causes cracks in brick on drying
  • Lime (CaO) in clay:
    • Reduces shrinkage on drying
    • Helps silica melt and bind on burning
    • Lowers fusion point in carbonated form
    • Excess lime causes bricks to melt and lose shape
    • Increases lime content to produce buff-burning bricks
  • Magnesia (MgO) in clay:
    • Affects color, making bricks yellow on burning
    • Causes clay to soften at a slower rate
    • Reduces warping
  • Iron (Fe) in clay:
    • Imparts red color on burning with excess oxygen
    • Improves impermeability and durability
    • Lowers fusion point, especially as ferrous oxide
    • Gives strength and hardness

Manufacturing of Bricks

  • Raw materials: clay, one of the most abundant natural mineral materials on earth
  • Phases of manufacturing:
    • Mining and storage of raw materials
    • Preparing raw materials
    • Forming the brick
    • Drying
    • Firing and cooling
    • De-hacking and storing finished products

Manufacturing Process

  • Mining and storage:
    • Surface clays, shales, and fire clays are mined in open pits
    • Raw materials are transported to plant storage areas
    • Storing sufficient quantities ensures continuous brick production
  • Preparation:
    • Breaking up large clay lumps and stones through size reduction machines
    • Processing through inclined vibrating screens to control particle size
  • Forming:
    • Three principal processes: stiff-mud, soft-mud, and dry-press
    • Stiff-mud process:
      • Mixing water with clay to produce plasticity
      • De-airing removes air holes and bubbles, giving clay increased workability and plasticity
    • Soft-mud process:
      • Mixing clay with 20-30% water
      • Forming into brick in molds
    • Dry-press process:
      • Mixing clay with minimal water (up to 10%)
      • Pressing into steel molds under pressure

Drying and Firing

  • Drying:
    • Wet brick contains 7-30% moisture, depending on forming method
    • Evaporating water in dryer chambers at temperatures ranging from 100°F to 400°F
    • Drying time varies with different clays, usually between 24 to 48 hours
  • Firing (burning):
    • Firing brick between 10 and 40 hours, depending on kiln type and variables
    • Types of kilns: tunnel kiln, periodic kiln
    • Fuel: natural gas, coal, sawdust, methane gas, or combination
    • Firing stages: final drying, dehydration, oxidation, vitrification, and flashing or reduction firing

Harmful Substances in Bricks

  • Lime:
    • Excess lime causes disintegration of bricks
    • Lime in lumps absorbs moisture, swells, and causes disintegration
  • Pebbles, gravels, and grits:
    • Do not allow clay to mix thoroughly
    • Spoil appearance of brick
    • Bricks with pebbles and gravels may crack
  • Organic matter:
    • On burning, organic matter gets charred, leaving pores
    • Increases water absorption, reduces strength
  • Alkalis (alkaline salts):
    • Excess alkalis make clay unsuitable for bricks
    • Melt clay on burning, making bricks unsymmetrical
    • Cause efflorescence (grey or white powder deposits) on bricks
  • Sulphur:
    • Found in clay as sulphate or iron sulphide
    • Causes formation of spongy, swollen structure in brick
    • Decolours brick with white blotches
  • Water:
    • Free water causes clay to shrink on drying
    • Combined water causes shrinkage on burning

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Description

This quiz covers the impact of silica, alumina, and lime on brick clay, including their effects on brick strength, plasticity, and burning. Learn how excess or deficiency of these components can affect brick quality.

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