Bricks
Bricks are the important building material. The top soil is pressed to form a square, or rectangular hard mass.
Composition
A good brick earth should have suitable proportions of alumina, silica, lime, iron oxide and magnesia.
Manufacture of bricks
The process of bricks manufacture involves,
(a) Preparation of brick earth.
(b) Moulding
(c) Drying
(d) Burning
(a) Preparation of good brick earth
It contains much process such as:
Removal of loose soil, Digging, spreading and cleaning, Weathering, Blending, Tempering.
(b) Moulding
The moulding of bricks can be done either by hand or by machine. It can table or grounf moulded. Machine modulated bricks have sharp edges and corners, smooth external surface and uniform texture.
(c) Drying
Drying is done on especially prepared drying yards. Bricks are dried for long period of 5 – 12 days.
(d) Burning
Burning is done in clamps or in kilns. Burning imparts strength and hardness to bricks. Bricks should be burnt properly. Under burning of bricks causes softness. If they are over burnt they are becoming brittle.
Hoffman’a Kiln
It is a continuous kiln where loading, firing, cooling, unloading occurs simultaneously. It is circular in plan. Chimney is placed in the centre of kiln and there are 12 chambers around the chimney. Each chamber is provided with; A main door for loading and unloading of bricks. Communicating doors between the compartments, a radial flue connected with central chimney. Fuel holes with covers, to drop fuel. Main doors are closed by constructing mud walls. For communicating doors are radial fuels, dampers are provided to shut or open them. In this type of kiln, each chamber performs various functions in succession namely, loading, drying, burning, cooling and unloading.
Size of bricks
The size of a standard bricks is 190*90*90 mm.
Test and characteristics of good bricks
>Shape and size bricks should be rectangular in shape with sharp edges and plane faces. Physical properties:
>Good bricks should be hard, sound and well burnt.
>It should give metallic ringing sound, when struck with another brick or hammer. It should have colour and fine compact texture.
>When bricks are dropped from a height of one meter on a hard surface, it should not breaks.
>Bricks should be free from fissures, cracks, pebbles, nodules of free lime etc.
Compressive strength
Good bricks should have high compressive strength of about 5 to 40N/mm^2 when tested on flat position.
Flexural strength
This is the resistance of the bricks to bending.
It varies from 7 to 20 N/mm^2.
Water Absorption
When bricks are immersed in cold water for about 24 hrs it should not absorbed more than 20 percent of its weight.
Presence of soluble salts the allowable percentage of soluble salts in bricks is 0.5 to 2.5.
>Bricks contain a higher percentage of soluble salts have poor resistance to weathering.
>Thermal conductivity and sound insulation>Building bricks should have high sound isulation and low thermal conductivity.
Fire Resistance
>The bricks possess very high resistance to fire.
>They are non-combustible and non-inflammable.
Expansion
>The bricks should not undergo a large change in volume on wetting.
>Excessive volume change indicates under-burnt nature of bricks.
Uses of bricks:
Bricks are mainly used for construction of walls. Bricks are mainly used in the construction of dam, piers bridges. Bricks moulded in the shape of a gutter can be used has drains. Hollow bricks are used for insulation purposes. High percentages are used ad refractory material. Fire bricks are used as refractory material. Sand lime bricks are used for ornamental purposes. Used in construction of chimneys and other special works.