There are different kinds of bricks which differ from the conventional building bricks with respect to their shape, specifications and special purpose for which they are made. Those bricks are discussed in the subsequent sections.
3.8.1 Specially Shaped Bricks
1. Bull-nosed Bricks
A brick moulded with a rounded angle is termed as the bull nose. It is used for rounded quoin. A quoin is a connection which is formed when a wall takes a smooth circular turn. The centre of the curved position is located on the long centre line of the brick (Fig. 3.8(a)).
Figure 3.8 Typical shapes of bull-nosed and cast bricks
2. Cant or Plinth Bricks
This has a slant-cum-straight edge at one end which is used in a plinth or in a door and window joints (Fig. 3.8(b)).
3. Circular Bricks
These bricks are provided with internal and external faces to be curved to meet the requirement of the particular curve and radius of the wall. These bricks are used for structures like towers, wells, etc. These bricks have to be specially made with a particular curvature (Fig. 3.9(a)).
4. Squint Bricks
These bricks have a special edge. These are used in the construction of active and obtuse squint quoins. Actual requirements should be provided for the manufacture of such bricks (Fig. 3.9(b)).
Figure 3.9 Typical shapes of circular and squint bricks
5. Coping Bricks
These bricks are made to suit the thickness of walls on which coping is to be provided. Different forms such as chamfered, half-round or saddle-back can be made (Fig. 3.10(a)).
Figure 3.10 Typical shapes of brick copings and a cornice brick
6. Cornice Bricks
In the construction of a cornice, different shapes are made to give a beautiful appearance. Such bricks are to be made especially for a particular purpose (Fig. 3.10(b)).
7. Perforated Bricks
These bricks are provided with cylindrical holes throughout their thickness (Fig. 3.11(a)). Because of holes the bricks are light in weight and easy to dry and burn. These are used for panel walls in small and multi-storeyed buildings. It provides maximum amount of ventilation, and the perforations are placed such that they do not permit the entry of rats or mices.
Figure 3.11 Typical shapes of perforated and clay hollow bricks
8. Hollow Clay Bricks
These bricks are made out of specially made homogeneous clay. They are uniform in colour and have a fine, compact and uniform texture. These bricks are of light weight. As bricks are hollow they provide insulation against heat, sound and dampness to the building (Fig. 3.11(b)).
9. Paving Bricks
Paving bricks are made from rock clay. The clay is burnt at a very high temperature than that of ordinary bricks. Paving bricks are used in roads and to resist the abrasive action of traffic. The paving bricks may be plain or chequered. These bricks are non-slipping and are hence preferred for street pavements, garden walks, etc. (Fig. 3.12).
Figure 3.12 Typical chequered paving brick
3.8.2 Refractory Bricks
Refractory bricks, also called Refractory Fire Bricks, are prepared from fire clay in the same manner as ordinary bricks. Refractory bricks contain about 30% alumina and 70% silica. After drying, they are burnt in kilns at high temperature ranging from 1400–1900°C. These bricks are yellowish white in colour.
As the fire bricks can resist high temperatures without softening or melting, they are used for the linings of interior surfaces of furnaces, chimneys, kilns, ovens, fireplaces, etc. The compressive strength of these bricks varies from 200–220 N/mm2, and the percentage absorption varies from 5–10.
3.8.3 Pressed Bricks
These bricks are made by pressing the clay to a high pressure of about 40 kg/sq.cm. They are directly burnt without drying. A special type of oil is used in the process which gives a glazed surface. The glazed surface may get peeled off when exposed to weather.
These bricks are of a regular shape, are compact and have high strength. These are used for decorative purposes of very high quality.
3.8.4 Sand–Lime Bricks
Autoclaved calcium silicate bricks are popularly known as sand–lime bricks. These bricks are made from a mixture of 95% of sand and 5% of lime (CaO) by weight. These bricks are hard, strong and are uniform in colour and texture. It presents a smooth and soft surface and hence may not be suitable for plastering. They are used for ornamental purposes.
3.8.5 Heavy-duty Bricks
These bricks are of very high quality, viz., high compressive strength, low water absorption, high durability and high bulk density. These bricks are free from any defects. They are used in heavy engineering works such as bridge structures, multi-storeyed buildings and industrial foundations.
3.8.6 Sewer Bricks
These bricks are manufactured using surface clay, fire clay or shale or a combination of these materials. They are used for the lining of walls, roofs and floors of sewers for ordinary domestic sewage. They are not suitable for industrial use as they are not acid resistant.
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