Characteristics of Good Bricks, Ingredients of Good Brick Earth, Functions of various ingredients etc
Characteristics of Good Bricks
The characteristics of a good brick are
- Size and Shape: The bricks should have uniform size and plane, rectangular surfaces with parallel sides and sharp straight edges.
- Color: The brick should have a uniform deep red or cherry color as indicative of uniformity in chemical composition and thoroughness in the burning of the brick.
- Texture and Compactness: The surfaces should not be too smooth to cause slipping of mortar. The brick should have precompact and uniform texture. A fractured surface should not show fissures, holes grits or lumps of lime.
- Hardness and Soundness: The brick should be so hard that when scratched by a finger nail no impression is made. When two bricks are struck together, a metallic sound should be produced.
- Water Absorption: Water Absorption should not exceed 20 per cent of its dry weight when kept immersed in water for 24 hours.
- Crushing Strength: Crushing strength should not be less than 10 N/mm2.
- Brick Earth: Brick earth should be free from stones, kankars, organic matter etc.
Ingredients of Good Brick Earth
For the preparation of bricks, clay or other suitable earth is moulded to the desired shape after subjecting it to several processes. After drying, it should not shrink and no crack should develop. Different ingredients present in the good quality brick earth have been shown in the figure below with their percentages.
Functions of various ingredients
The functions of different substances present in the brick earth have been explained below,
It enables the brick to retain its shape and imparts durability, prevents shrinkage and warping. Excess of silica makes the brick brittle and weak on burning.
Alumina absorbs water and renders the clay plastic. If alumina is present in excess of the specified quantity, it produces cracks in brick on drying.
Normally lime is added less than 10%. The benefits are,
- Reduces the shrinkage on drying.
- Causes silica in clay to melt on burning and thus helps to bind it.
- In carbonated form, lime lowers the fusion point.
- Excess of lime causes the brick to melt and the brick lose its shape.
- Red bricks are obtained on burning at considerably high temperature (more than 800°C) and buff-burning bricks are made by increasing the lime content.
Mangnesia is rarely exceeding 1 per cent, affects the colour and makes the brick yellow, in burning; it causes the clay to soften at slower rate than in most case is lime and reduces warping.
Iron oxide constituting less than 7 per cent of clay, imparts the following properties:
- Gives red colour on burning when excess of oxygen is available and dark brown or even black colour when oxygen available is insufficient, however, excess of ferric oxide makes the brick dark blue.
- Improves impermeability and durability.
- Tends to lower the fusion point of the clay, especially if present as ferrous oxide.
- Gives strength and hardness.
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