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Bricks in civil engineering
Bricks in civil engineering in Hindi
Composition of bricks
Bricks

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What is brickThe common brick is one of the oldest building material and it is extensively used at present as a leading material of construction because of its durability, strength, reliability, low cost, easy availability, etc.The bricks are obtained by moulding clay in rectangular blocks of uniform size and then by drying and burning these blocks. As bricks are of uniform size, they can be properly arranged and further, as they are light in weight, no lifting appliance is required for them.
Uses of brick Brick plays very important role in the field of civil engineering construction. Bricks are used as an alternative of stones in construction purpose. Here some main uses of construction brick are given below.1-Construction of walls of any size 2-Construction of floors 3-Construction of arches and cornices 4-Construction of brick retaining wall 5-Making Khoa (Broken bricks of required size) to use as an aggregate in concrete 6-Manufacture of surki (powdered bricks) to be used in lime plaster and lime concrete.
Composition of Good Brick There are 5 major ingredients of brick. The general percentage of these ingredients in brick is given below:Ingredient Percentage in brick
Alumina (Al2O3) 20% to 30%
Silica (SiO2) 50% to 60%
Lime(CaO) not exceeding 5%
Iron Oxide (Fe2O3) 5%-6%
Magnesia (MgO) 5%
Alumina is the main constituent of clay. It acts as a cementing material in raw brick. Brick clay is plastic due to the presence of alumina. This plasticity ensures that bricks can be molded.If alumina is present in excess, with inadequate quantity of sand, the raw bricks shrink and warp during drying and burning and become too hard when burnt.
Good quality bricks contain 50-60% silica. It is present in both free and combined form.As frees sand, it remains mechanically mixed with clay. In combined form, it reacts with alumina to form aluminosilicates. Silica prevents raw bricks from cracking, shrinking and warping. The higher the proportion of sand, the more and shapely and uniform in texture will be the brick. It increase water resistant and weather resistant in brick. Although, excess silica destroys cohesion between the brick clay particles and makes brick brittle and weak. The durability of bricks largely depends upon the proper proportion of silica and alumina.
Bricks should contain a little amount of finely powdered lime. The lime prevents shrinkage of raw bricks. It enables silica to melt at the furnace temperature of 1650oC and binds the particles of brick together resulting in strong and durable bricks. At about 1100 C, lime acts as a catalyst to elevate the furnace temperature to 1650 C at which silica fuses. This slightly fused silica works as a strong cementing material. Excess lime in brick clay causes bricks to melt, as more than the required amount of silica will fuse. The bricks then lose their shape and become disfigured.
A small quantity of oxide of iron to the extent of about 5% to 6% is desirable in good brick earth. It helps as lime to fuse sand. It also imparts red color to the bricks. The excess of oxide of iron makes the bricks dark blue or blackish. If, on the other hand, the quantity of iron oxide is comparatively less, the bricks will be yellowish in color.
A small quantity of magnesia in brick earth imparts yellow tint to the bricks and decreases shrinkage. But excess of magnesia leads to the decay of bricks.
Qualities of Good Bricks The good bricks which are to be used for the construction of important structures should possess the following qualities:(i) The bricks should be well-burnt in kilns, copper-colored, free from cracks and with sharp and square edges. The color should be uniform and bright. (ii) The bricks should be uniform in shape and should be of standard size. (iii) The bricks should give a clear metallic ringing sound when struck with each other. (iv) The bricks when broken or fractured should show a bright homogeneous and uniform compact structure free from voids.