Bricks Building Materials

Classification of Bricks

This article is on the Classification of Bricks Based on Quality. In this article, you will learn about the different classes of bricks with important characteristics/properties.

This article will be helpful and informative for civil engineers and civil engineering students.

You may also love to read: 10 quality of bricks used in building construction

Classification of Bricks

1. First Class brick

First-class brick is mainly used for load-bearing walls for multi-story buildings.

Characteristics of first-class brick are as follows:

  1. Color: Uniform dark red color
  2. Size and Shape: Should have a standard size and have a smooth surface free from
    cracks and should have sharp edges
  3. Soundness: When two bricks stuck together, they should give metallic sound.
  4. Hardness: It should be hard that it could not be scratched by fingernails.
  5. Porosity: It should not absorb water more than 15 % of its dry weight when immerse-
    in water for 24 hrs
  6. Strength: Minimum crossing strength should not be less than 140 kg/cm2
  7. Water absorption should be less than 15 % of its dry weight.
  8. Durability: Should be able to resist the effects of weathering agencies like temperature variations, rain, frost action, etc.
  9. Efflorescence: Should not contain alkaline salts which may cause efflorescence
    on its surface and decay the bricks.

2. Second Class Brick

Second class bricks are not suitable for the load-bearing walls for more than two-story buildings.

Characteristics of second class brick are as follows:

  1. It should not absorb water more than 20% to 22% of its dry weight when immersed in water for 24 hrs.
  2. The compressive strength of second class bricks is between 70 to 140 kg/cm2.
  3. Medium red in color.
  4. The shape and size are good.
  5. These bricks are burnt well.

3. Third Class Brick

The third class of bricks is generally used for temporary works.

Characteristics of third class brick are as follows:

  1. It should not absorb water more than 22% to 25% of its dry weight when immersed in water for 24 hrs.
  2. The compressive strength of third class bricks is between 35 to 70 kg/cm2.
  3. Light red in color.
  4. The shape and size are poor
  5. These bricks are not burnt well and weak.

You may also searching for: Properties of Bricks

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Bricks Building Materials

Composition of Brick

Bricks may define as a structural unit of rectangular shape and convenient site that is made from suitable types of clays by different processes involving molding, drying, and burning. In this article, you will learn about the materials used to make brick and its properties.

Even at present, brick is the most basic and favored material for common constructions though out the world.

The popularity of brick as a material of constructions is because of their local and cheap availability, strength, durability, reliability and insulating property against heat and sound.

Composition of brick or materials used in making brick

In general, it is observed that any soil that contains one-fourth part of clay and three by fourth parts of sand and silt is suitable for making bricks.

Good brick earth should be such that when prepared with water it can be easily molded dried and burnt without cracking or warping. It should contain a small quality at finely divided lime to help in binding the particles of brick together by melting the particles of sand.

A little oxide of iron should also be present which would give the brick its peculiar red color and act as a flux in the same manner as lime.

However, suitable brick earth should have various constituents in the following proportion.

i) Alumina or clay (20% – 30%)

  1. It shows the plastic character to the clay in wet conditions and is capable of being molded to any shape.
  2. When alumina is greater than 30% brick will become more plastic and also shrink more and develop cracks on drying.
  3. If less than 20%, it may be difficult to mold to proper shapes and develop cracks on a molding. So it provides plasticity resistance against shrinkage and makes the brick hard.

ii) Silica or sand (50% to 60%)

  1. Silica is present in much clay in two forms as a constituent of clay minerals and also as free. It is in the form of sand or quartz.
  2. Silica is infusible except at very high temperature but in the presence of alumina is nearly equal proportions and the oxide of iron it fuses at low temperature.
  3. Unlike the silicate of Alumina, its presence in clay produces hardness, resistance to heat, durability and prevents shrinkage and warping.
  4. Excess of it makes the bricks brittle.

iii) Lime (4% to 6%)

  1. When present in small quantities in the finely divided state it reduces shrinkage of brick, helps silica to melt at lower temperature and binds the particles of the brick together resulting in greater strength of brick.
  2. Excess of lime causes the brick to melt and lose its shape.

You may also love to read: 10 quality of bricks used in building construction

iv) Iron oxide (4% to 6%)

  1. Iron oxide acts as a flux, it lowers down the softening temperature of silica and other clay components during firing.
  2. The iron oxide imparts the very characteristic red color to the burnt brick.
  3. The excess of iron oxide makes the brick too soft during the burning stage, they suffer deformation in shape and make the dark blue color.
  4. A deficiency of iron oxide in the clay may make their burning difficult and also give then a yellowish appearance.

v) Magnesia: (1% to 2%)

  1. Small qualities at magnesia in brick earth make the brick of yellowish color and reduce shrinkage.
  2. But excess of magnesia leads to the delay of bricks.

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