Types of Bricks in Construction
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Questions and Answers

What is the primary factor that affects the limit of water absorption in bricks?

  • Compressive strength
  • Type of brick class (correct)
  • Type of Government organization
  • Weathering conditions

    • What is the recommended use of First Class Bricks?

  • Building temporary structures
  • Foundation and floors in lime concrete and road metal
  • Pointing, exposed face work, flooring, and reinforced brick work (correct)
  • Hidden masonry works

    • What is the main difference between First Class Bricks and Second Class Bricks?

  • Color and texture
  • Weight and size
  • Crushing strength
  • Small cracks and distortions are permitted (correct)

    • What is the minimum crushing strength required for Second Class Bricks?

    <p>7.0 N/mm2</p> Signup and view all the answers

    What is the characteristic of Third Class Bricks?

    <p>Under burnt, soft, and light-colored</p> Signup and view all the answers

    What is the primary use of Fourth Class Bricks?

    <p>Foundation and floors in lime concrete and road metal</p> Signup and view all the answers

    What is the purpose of the saturation coefficient in ASTM C62?

    <p>To classify bricks according to weathering conditions</p> Signup and view all the answers

    What is the recommended application of Grade SW bricks?

    <p>Areas subjected to frost action, especially at or below ground level</p> Signup and view all the answers

    What is the consequence of using highly absorptive bricks?

    <p>Efflorescence and other problems in the masonry</p> Signup and view all the answers

    What percentage of the volume of the brick is permitted for small holes?

    <p>25 per cent</p> Signup and view all the answers

    What is the purpose of silica in brick making?

    <p>To prevent shrinkage and warping</p> Signup and view all the answers

    What should be the colour of a good brick?

    <p>Uniform deep red or cherry colour</p> Signup and view all the answers

    What should be the texture of a good brick?

    <p>Precise and uniform to prevent slipping of mortar</p> Signup and view all the answers

    What should be the minimum crushing strength of a good brick?

    <p>10 N/mm2</p> Signup and view all the answers

    What is the maximum percentage of water absorption of a good brick?

    <p>20 per cent of its dry weight</p> Signup and view all the answers

    What should be the shape of a good brick?

    <p>Uniform size and plane, rectangular surfaces with parallel sides</p> Signup and view all the answers

    What should be the characteristics of the surface of a good brick when scratched by a finger nail?

    <p>No impression is made</p> Signup and view all the answers

    What should be the sound produced when two bricks are struck together?

    <p>A metallic sound</p> Signup and view all the answers

    What is the purpose of the final drying stage in a tunnel kiln?

    <p>To evaporate free water from the bricks</p> Signup and view all the answers

    What is the temperature range for the dehydration stage in a tunnel kiln?

    <p>149 ºC to 982 ºC</p> Signup and view all the answers

    What is the purpose of the cooling stage in a tunnel kiln?

    <p>To change the color of the bricks</p> Signup and view all the answers

    What is the maximum time for the cooling process in tunnel kilns?

    <p>10 hours</p> Signup and view all the answers

    What is the purpose of de-hacking in brick manufacturing?

    <p>To unload the kiln cars after the bricks have cooled</p> Signup and view all the answers

    What is the effect of excess lime in the clay?

    <p>It changes the color of the brick from red to yellow</p> Signup and view all the answers

    What is the effect of organic matter in the clay?

    <p>It makes the bricks porous</p> Signup and view all the answers

    What is the role of alkalis in the clay?

    <p>They are of great value as fluxes</p> Signup and view all the answers

    What is the effect of pebbles and gravels in the clay?

    <p>They do not allow the clay to be mixed thoroughly</p> Signup and view all the answers

    What happens to the bricks when they come in contact with moisture?

    <p>The alkalis in the brick crystallize and a grey or white powder forms on the surface</p> Signup and view all the answers

    What is the recommended way to remove efflorescence from a brick surface?

    <p>Dry brush it away before rendering or plastering</p> Signup and view all the answers

    What is the effect of sulphur in clay on the brick structure?

    <p>It forms a spongy, swollen structure and decolours the brick</p> Signup and view all the answers

    What type of water can cause similar effects as sulphur in clay?

    <p>Water containing small quantities of magnesium or calcium carbonates</p> Signup and view all the answers

    What happens to the brick when it contains carbon and insufficient time is given for proper oxidation during burning?

    <p>The sulphur forms a spongy, swollen structure and decolours the brick</p> Signup and view all the answers

    What is the main reason for the formation of efflorescence on bricks?

    <p>The absorption of moisture by the brick and subsequent crystallization of alkalis</p> Signup and view all the answers

    What is the effect of free water on clay during drying?

    <p>It causes the clay to shrink considerably</p> Signup and view all the answers

    Why is it important to remove efflorescence before rendering or plastering a wall?

    <p>To prevent the salts from being carried back into the wall and reappearing later</p> Signup and view all the answers

    What is the effect of combined water on clay during burning?

    <p>It causes the clay to shrink considerably</p> Signup and view all the answers

    What is a necessary property of clay for brick manufacturing?

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

    What is the primary difference between surface clays and shales?

    <p>Physical structure</p> Signup and view all the answers

    What is the purpose of mixing clays from different sources and locations?

    <p>To minimize variations in chemical composition and physical properties</p> Signup and view all the answers

    What is a characteristic of fire clays?

    <p>Usually mined at deeper levels</p> Signup and view all the answers

    What do surface clays and fire clays have in common?

    <p>Chemical composition</p> Signup and view all the answers

    What is a result of varying manufacturing processes?

    <p>Compensation for differences in chemical composition</p> Signup and view all the answers

    What can be said about brick from different manufacturers with the same appearance?

    <p>They have different properties</p> Signup and view all the answers

    What is the common composition of all three types of clay?

    <p>Silica, alumina, and varying amounts of metallic oxides</p> Signup and view all the answers

    What is the result of mixing clays from different sources and locations in the pit?

    <p>Bricks with the same properties in each production run</p> Signup and view all the answers

    Study Notes

    Classification of Bricks

    • First-class bricks: recommended for pointing, exposed face work, flooring, and reinforced brick work
    • Second-class bricks: permitted to have small cracks and distortions, higher water absorption (16-20%), and crushing strength not less than 7.0 N/mm2
    • Third-class bricks: under-burnt, soft, and light-colored, producing a dull sound when struck; water absorption is about 25% of dry weight
    • Fourth-class bricks: over-burnt, badly distorted, and brittle; used for ballast in foundation and floors in lime concrete and road metal

    Strength and Durability

    • Clay building bricks are graded according to properties related to durability and resistance to weathering
    • ASTM C62 classifies three available grades: severe weathering (SW), moderate weathering (MW), and negligible weathering (NW)

    Characteristics of Good Bricks

    • Size and shape: uniform size and plane, rectangular surfaces with parallel sides and sharp straight edges
    • Color: uniform deep red or cherry color
    • Texture and compactness: surfaces not too smooth, pre-compact and uniform texture
    • Hardness and soundness: hard enough to prevent scratching with a finger nail, producing a metallic sound when struck
    • Water absorption: not exceeding 20% of its dry weight when kept immersed in water for 24 hours
    • Crushing strength: not less than 10 N/mm2
    • Brick earth: free from stones, kankars, organic matter, saltpetre, etc.

    Ingredients of Good Bricks

    • Clay used for brick making consists mainly of silica and alumina, mixed with small proportions of lime, iron, manganese, sulphur, etc.
    • Functions of various ingredients:
      • Silica: enables the brick to retain its shape, imparts durability, and prevents shrinkage and warping
      • Alumina: mixed with silica in a proportion that makes the clay plastic when water is added

    Types of Clay

    • Three principal forms: surface clays, shales, and fire clays
    • Surface clays: found near the surface of the earth, may be the up thrusts of older deposits or of more recent sedimentary formations
    • Shales: clays subjected to high pressures until they have nearly hardened into slate
    • Fire clays: usually mined at deeper levels, have refractory qualities

    Manufacturing Process

    • Tunnel kiln: brick are loaded onto kiln cars, which pass through various temperature zones
    • Firing stages: final drying, dehydration, oxidation, vitrification, and flashing or reduction firing
    • Cooling: important stage in brick manufacturing, affects color

    Harmful Substances in Bricks

    • Lime: when in excess, changes the color of the brick from red to yellow and causes disintegration
    • Pebbles, gravels, and grits: do not allow the clay to be mixed thoroughly, spoil the appearance of the brick, and may cause cracking
    • Organic matter: increases water absorption, reduces strength, and makes bricks porous
    • Alkalis: when in excess, melt the clay on burning, make bricks unsymmetrical, and cause efflorescence
    • Sulphur: when present with carbon, causes the formation of a spongy, swollen structure in the brick and decolouration by white blotches
    • Water: excessive free water causes clay to shrink, while combined water causes shrinkage during burning

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