BRICKS
Introduction
Brick
is a clay product. It is rectangular in shape . It is made to a length of twice
the width plus thickness of mortar joint. Its thickness is less than its width.
It is handy and light in weight. It is used as a leading material for
construction, because of its tow cast, durability, strength, reliability, easy
availability etc.,
Brick Earth
The main raw material for brick is soil
consisting of extremely small crystalline particles of one or more members of a
small group of minerals are commonly known as the clay minerals. Non clay
minerals such as quarts, calcite, feldspar and pyrite, organic material and water-soluble
salts present in soils also influence the properties of bricks.
Clay may also be
defined as the weathered products of the silicate rock containing sufficient
hydrous silicate of alumina in the softened condition to produce a plastic or
semi - plastic mass when mixed with water.
Composition of good brick earth
The constituents of
good brick earth are
1. Alumina
2. Silica
3. Lime
4. Magnesia
5, Oxide of
iron
Alumina
It is a basic constituent . it readily absorb
water and imparts plasticity to the clay so that it can be moulded. A good brick
earth should contain about 20 to 30% of alumina. Excess of it causes the raw
brick to shrink and warp during and burning.
Silica
It is a very
important constituent. If exists in clay both in free state and combined state.
If prevents shrinkage, warping cracking and undue hardness of the brick. If
thus imparts uniform shape and makes the brick durable. A good brick earth
should contain about 50 to 60% silica. Excess of silica destroys cohesion and
makes the brick brittle and weak.
Lime
A small proportion of
lime must be present in good brick earth. If should be present in a very finely
powdered form time prevents shrinkage of raw bricks. It acts as a flux and
causes the sand to fuse and bind the particles together. Lumps of lime become
quick lime after burning. This quick lime slakes and expands in the presence of
moisture. This action causes the brick to spilt into: pieces.
Magnesia
A small quantity of magnesia gives yellow tint
to brick and decreases shrinkage. If in excess, it causes the brick to decay.
Oxide of iron
A small quantity (5
to 6%) of oxide of iron must be present in good brick earth. It helps to fuse
sand a little at low 1.18 temperatures. If also imparts a pleasing red
colour to brick. Excess of oxide of iron makes the bricks dark blue or
blackish colour.
The general
proportions of brick earth
1. Silica 50 to 60%
2. Alumina 20 to 30%
3. Lime 10%
4. Magnesia < 1%
5. Oxide of iron <
7%
Properties of bricks
1. Size
Size of the bricks should be standard as prescribed by IS . (19cm x 9cm x 9cm
2. Shape
Bricks should be uniform in shape with sharp
edges.
3. Colour
The colour should be uniform and bright.
4. Structure
A good brick should show fine compacts and uniform structure.
5. Soundness
A good brick should give a clear metallic sound when struck with another brick
6. Hardness
A good brick should be so hard that finger nails should not
be able to make any marks on its surface when scratched.
7. Porosity
A good brick should absorb more than 20% of its
dry weight of water when kept immersed for 24 hours.
8.
Strength
The minimum crushing strength of a good brick is 10.5 N/mm2.
9. Resistance of fire
A good brick should have resistance to
fire.
Next - Lime
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