Bricks:
The bricks had been produced since the dawn of civilization.the oldest shaped bricks found date back to 7500 BC. One of the largest brick structures in the world has been found in Sri Lanka.
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.
The bricks do not require dressing and the art of laying bricks is so simple that the brickwork can be carried out with the help of unskilled labourers. Thus, at places where stones are not easily available, but if there is plenty of clay suitable for the manufacture of bricks, the bricks replace stones.The 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.Composition of Good Brick Earth:
Following are the constituents of good brick earth:
(1) Alumina: It is the chief constituent of every kind of clay. A good brick earth should contain about 20% to 30% of alumina. This constituent imparts plasticity to the earth so that it can be moulded. 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.
(2) Silica : It exists in clay either as free or combined. As free sand, it is mechanically mixed with clay and in combined form, it exists in chemical composition with alumina. A good brick earth should contain about 50 per cent to 60 per cent of silica. The presence of this constituent prevents cracking, shrinking and warping of raw bricks. It thus imparts uniform shape to the bricks. The durability of bricks depends on the proper proportion of silica in brick earth. The excess of silica destroys the cohesion between particles and the bricks become brittle.
(3) Lime : A small quantity of lime not exceeding 5 per cent is desirable in good brick earth. It should be present in a very finely powdered state because even small particles of the size of a pin-head cause flaking of the bricks. The lime prevents shrinkage of raw bricks. The sand alone is infusible. But it slightly fuses at kiln temperature in presence of lime.
Such fused sand works as a hard cementing material for brick particles. The excess of lime causes the brick to melt and hence its shape is lost. The lumps of lime are converted into quick lime after burning and this quick lime slakes and expands in presence of moisture. Such an action results in splitting of bricks into pieces.
(4) Oxide of iron : A small quantity of oxide of iron to the extent of about 5 to 6 per cent is desirable in good brick earth. It helps as lime to fuse sand. It also imparts red colour 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 colour.
(5) Magnesia : 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:
- The bricks should be table-moulded, well-burnt in kilns, copper-coloured, free from cracks and with sharp and square edges. The colour should be uniform and bright.
- The bricks should be uniform in shape and should be of standard size.
- The bricks should give a clear metallic ringing sound when struck with each other.
- The bricks when broken or fractured should show a bright homogeneous and uniform compact structure free from voids.
- The brick should not absorb water more than 20 per cent by weight for first class bricks and 22 per cent by weight for second class bricks, when soaked in cold water for a period of 24 hours.
- The bricks should be sufficiently hard. No impression should be left on brick surface, when it is scratched with finger nail.
- The bricks should not break into pieces when dropped flat on hard ground from a height of about one metre.
- The bricks should have low thermal conductivity and they should be sound-proof.
- The bricks, when soaked in water for 24 hours, should not show deposits of white salts when allowed to dry in shade.Tests for Bricks:
A brick is generally subjected to the following tests to find out its suitability for the construction work:
- Absorption
- Crushing strength
- Hardness
- Presence soluble salt
- Soundness
- Structure
- Shape and size
• Shape and size:
In this test, a brick is closely inspected. It should be of standard size and its shape should be truly rectangular with sharp edges. For this purpose, 20 bricks of standard size (190 mm X 90 mm X 90 mm) are selected at random and they are stacked lengthwise, along the width and along the height.
For good quality bricks, the results should be within the following permissible limits:
| Length |
3680mm to 3920mm |
| Width |
1740mm to 1860mm |
| Height |
1740mm to 1860mm |
Classification of Bricks :-
The bricks can broadly be divided into two categories as follows:
- Un-burnt or sun-dried bricks
- Burnt bricks
Un-burnt brick:
The un-burnt or sun-dried bricks are dried with the help of heat received from sun after the process of moulding. These bricks can only be used in the construction of temporary and cheap structures. Such bricks should not be used at places exposed to heavy rains.
The bricks used in construction works are burnt bricks and they are classified into the following four categories:
(1) First class bricks
(2) Second class bricks
(3) Third class bricks
(4) Fourth class bricks.Uses of Bricks:
Following are the uses of bricks:-
(i) The first class and second class bricks are widely used for all sorts of sound work especially of permanent nature. These structures include buildings, dams, roads, sewers, bridge piers, tunnels, pitching works, etc.
(ii) The use of first class bricks is specified for obtaining the architectural effects on faces of structures where they are to be kept exposed for beauty.
(iii) The masonry with second class bricks is generally plastered to make the smooth surface obtained due to the irregular shape and size of bricks. The mortar required in brick masonry using second class bricks will also be more.
