What is Bricks?
Brick is one of the oldest and popular building materials used nowadays because of being cheap, durable, and easy to handle and work with. Bricks are light in weight therefore bricks replace stones. It is rectangular in shape and can be conveniently handled with one hand. Bricks are obtained by molding clay and then by drying and burning these blocks.
Composition of Bricks
It is one of the major constituents of every clay. A brick should contain alumina in between 20 to 30 %. Alumina in brick earth provides plasticity so that it can be molded easily. If alumina is in huge quantity, raw bricks may lead to shrink and warp during drying and burning.
Good brick earth should contain about 50 to 60 % of silica. Silica provides the bulk to brick earth, uniform Shape and size of brick is maintained by Silica. It exists in clay in free or combined form. Silica is helpful for the prevention of cracking, shrinking, and warping of raw bricks. Excess of silica mat leads to the destruction of the cohesion between particles and bricks become brittle.
A small quantity of lime is desirable to reduce the shrinkage in brick and brick will be denser but excess lime deforms the shape of a brick. If lime is present in form of lumps after burning the brick unsoundness will take place.
4. Oxides of Iron
A small quantity of oxide of iron of 5 to 6% imparts reddish-brown color. It also helps in using lime and silica. Excess of iron can lead the bricks to dark blue or blackish.
Less than 1% of magnesia is provided in brick and it imparts a yellow tint to brick and decreases shrinkage. Excess magnesia leads to the decay of brick.
Properties and Tests of Bricks
- The brick should have uniform color, homogeneous, compact, and sharp edges.
- The weight of one brick should be in the range of 3 to 3.5kg and the bulk density of brickwork is 1800kg/m³.
- The dimension of brick should be as per standard
- Standard Size (Modular size): 19cm x 9cm x 9cm
- Modular size with mortar: 20cm x 10cm x 10cm
- Conventional size: 23cm x 11.4cm x 7.6cm
- Brick should not break when it is dropped over a flat surface from a height of 1m.
- As per IS 1077 brick is classified as per its strength and the minimum strength of brick should not be less than 3.5 MPa when placed in a compression testing machine.
- There should be no sign of scratch over the brick surface when it is scratched by fingernails.
- The brick should produce a clear ringing sound when stuck with each other.
- There should be no patches or stain over the surface of the brick after soaking it in water for 24hrs.
- Broken brick should show a bright homogeneous and compact structure that is free from voids.
- The 1st class brick should not absorb more than 20% water by weight when it is immersed in a water tank for 24hrs.
- This is valid up to 12.5 MPa strength. For higher strength, it should not be greater than 15%.
Types of Bricks and their Application
1. Types of bricks on the basis of burning
A) Unburnt or Sundried brick
They are dried with the heat received by the sun after molding. They are used at a cheap and temporary structure and cannot be used where heavy rainfall occurs.
B) Burnt brick
They are burnt in clamp or kiln and are classified in the following categories:
- First-class brick: They are table molded and have a standard shape and smooth surface and sharp edges. They are used in superior works of a permanent structure.
- Second class brick: They are ground molded and kiln burnt brick. The surface is slightly rough and the edges are slightly irregular. They are used where plaster coating is provided over brickwork.
- Third-class brick: They are molded in-ground and burnt in the clamp. They are not hard and their surfaces are rough with distorted edges. They are used at a place that is of less importance, temporary structures, and where rainfall is less.
- Fourth class brick: They are over burnt brick, irregular shape, and dark color. They are used in foundations, floors, roads because they are over burnt so sometimes they show strength higher than first-class brick.
2. Types of bricks on the basis of Special Purpose
They are formed to meet the ornamental decoration of the structure.
A) Bull Nosed brick
They have a round edge at one side and used where a sharp edge is not required.
B) Perforated brick
In this brick huge number of perforates is provided along with its thickness. They are easily burnt and light in weight. They are used for non-load-bearing walls, partition walls.
C) Hollow brick
One or more cavities are provided in this brick. They are also light weighted and used where insulation is required against heat.
D) Circular brick
Both the faces of brick are curved of a particular radius to meet the required demand. Used for wells and towers.
3. Grading of bricks based on IS 1077: 1992 code specification
- According to IS code, Bricks with compressive strength not less than 140kg/cm2 –Grade A-A class.
- Bricks having a compressive strength of more than 105kg/cm2 – First class bricks – Grade A.
- Bricks having compressive strength not less than 70kg/cm2 –Second class bricks – Grade B.
- Bricks with compressive strength should not less than the average value in any case 35 kg/ cm2 – class III bricks – Grade C.