Ingredients of good brick
The main ingredient of brick is clay which mainly consists silica and alumina. The brick clay shall be such that after drying, it should not shrink and do not show any shrinkage cracks.
The proportion of various ingredients are as follows
Functions of various ingredients
Silica
Silica gives brick it's strength, toughness and durability;
However, excess of silica makes the brick brittle and weak.
Alumina
Alumina gives brick plasticity when water is added;
Excess of alumina produces shrinkage cracks on drying.
Lime
Lime reduces the shrinkage on drying,
Lime causes silica in clay to melt on burning thus helps in binding,
Excess of lime causes brick to melt during burning results in losing of shape
Magnesia
Magnesia barely 1%, affects the colour of brick yellow.
Iron
Iron gives red colour on burning when oxygen is available & dark brown when oxygen is insufficient,
Excess of iron makes the brick dark blue,
Improves impermeability and durability,
Gives strength and hardness.
Characteristics of good brick
Size and shape
Uniform size, plane rectangular surface, parallel sides, sharp and straight edges.
Colour
Uniform deep red colour (indicates proper chemical composition and burning)
Texture
Compact and uniform texture
Hardness and soundness
Should not make impression when scratched by finger nail, metallic sound should produced when stuck with another brick
Crushing strength
Not less than 10.5 N/mm²
Water absorption
Should not exceed 20 % of its dry weight when immersed in water for 24 hours.
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