Bricks are the building blocks of the modern masonry structures. Bricks are rectangular blocks of uniform size that are hardened by heating or chemical processes. There are different types of bricks available in the market such as solid or hollow bricks, interlocking bricks, clay bricks, fly ash, concrete, plastic pellets, lime, silica, recycled materials, and special types of bricks used for structures exposed to severe conditions like chemical factories, autoclaves etc.
Types Of Bricks Used In Construction:
The bricks can be broadly classified into:
1. Clay bricks.
2. Sand lime or Calcium silicate bricks.
3. Concrete bricks.
4. Fly ash bricks.
5. Fire bricks.
6. Engineering bricks.
1. Clay Bricks:
The clay bricks are the oldest of bricks to be invented by man. They date as back as 12000 years ago. The clay bricks are widely used for construction purposes. But there are many types of clay bricks available in the market. Based on the hardening process, the bricks can be divided into
1) Sun Dried bricks or Unburnt bricks.
2) Burnt bricks.
1) Sun Dried Bricks Or Unburnt Bricks:
These bricks are made by preparing the earth or the base material and moulded on the ground and allowed to harden through natural sunlight. They are weak and cannot be used for permanent buildings. This type of bricks can be used to build temporary structures like huts.
i. Easy to make.
ii) They are cheap.
i) These bricks have low compressive strength, low resistance to water penetration and weather exposure.
ii) They cannot be used to build permanent structures.
2) Burnt Bricks:
Burnt bricks are either table moulded or ground moulded. They are burnt in kilns, autoclaves or clamps. Burning increases the strength of the brick and makes it more robust. However, there are four classes in the burnt bricks based on their quality. They are as follows:
A. First Class Bricks:
The first-class bricks are the highest quality burnt bricks. They are table moulded and wire cut. They are heated in kilns and allowed to dry. They are uniform in shape and colour and have clearly defined edges. They can be used for pavements, walls of permanent structures and even for ornamental purposes.
Advantages Of First Class Bricks:
i) They have higher compressive strength of minimum 10.5 N/mm2
ii) They can be used for permanent structures.
iii) They have even surfaces thus easing the finishing processes like plastering.
iv) They can be used to improve the facade of the building.
v) They can be used as load bearing walls
vi) The water absorption will not be more than 15 %.
Disadvantages Of First Class Bricks:
i) They cannot be used for cold weather regions that are susceptible to freeze and thaw conditions.
ii) They expand slightly with time.
iii) They are prone to chemical attacks
iv) Burning of bricks is not sustainable to the environment.
v) They need to be soaked in water before using them
B. Second Class Bricks:
These bricks are made using the same method but due to poor supervision, they may be slightly over burnt. They have slight hair cracks and small irregularities on the surface. They can be used in buildings where the walls will be plastered, as a brick ballast in concreting and some load bearing buildings.
Advantages of Second Class Bricks:
i) They can be used in permanent structures with plastering on them.
ii) They can be used for single storeyed load bearing structures.
Disadvantages Of Second Class Bricks:
In addition to the disadvantages of the first-class bricks,
i) The water absorption is 22% thus making it more susceptible to seepage and freeze thaw cycles.
ii) They don’t have well defined edges
iii) The minimum compressive strength is only 7 N/mm2.
C. Third Class Bricks:
These bricks are table moulded but burnt in clamps instead of kilns. This imparts poor quality to the bricks. These bricks are slightly under burnt. This type of bricks can be used for non-load bearing walls, boundary walls, low rise walls, etc,
i) They are cheap.
In addition to the disadvantages of the second-class bricks,
i) The water absorption is 25% thus making it more susceptible to seepage and thus cannot be used in areas with heavy rains.
ii) They don’t have well defined edges or smooth finishes.
iii) The minimum compressive strength is only 3.5 N/mm2.
D. Fourth Class Bricks:
These bricks are also called as rejected bricks and are very similar in properties and quality to the unburnt bricks. They are over burnt and thus very weak and cannot be used as a building block. They are of non uniform shape, colour and size. They can be used as a filling material or be grinded into a powder to make the wearing coats called Surkhi on the terrace.
2. Sand lime Or Calcium Silicate Bricks:
Sand lime or Calcium silicate bricks also known as the flint lime brick is made up of calcium and silica. Unlike clay bricks, these bricks are not hardened by burning. These are hardened by chemical processes. Various pigments can be added to the bricks to produce different colours of bricks such as black, green, grey, red, brown and yellow.
i) Due to the impressive colours, they can be used for ornamental purposes.
ii) They have a compressive strength of 10 N/mm2.
iii) They have a smooth finish thus demanding less amount of plastering.
iv) They produce greater fire resistance than the clay bricks.
v) They provide sound insulation and improve the acoustics of the building.
vi) They perform well against efflorescence.
i) They have low abrasive strength and hence cannot be used for wearing surfaces like pavements, sidewalks etc.,
ii) They can shrink after placing. Special considerations have to be taken to counteract the shrinking of the bricks.
3. Concrete Bricks:
The concrete bricks are made up of cement, aggregates and water. They are not used widely because of the availability of the concrete wall panels. Concrete bricks, like sand lime bricks can be fashioned in different colours.
Advantages Of Concrete Bricks:
i) It has higher compressive strength than the clay bricks.
ii) It provides a very pleasing sight and can be used for the façade of the building.
iii) They have a smooth finish thus demanding less amount of plastering.
iv) They provide greater fire resistance than the clay bricks.
Disadvantages Concrete Bricks:
i) Concrete bricks shrink and thus cannot be used for foundations.
ii) The maximum lifespan of a concrete brick is only 65 years.
iii) It does not resist acid attack or efflorescence
iv) The manufacturing process produces greenhouse gases.
4. Fly Ash Bricks:
These are made up of Class C or Class F fly ash, cement, fine aggregate and water. All the ingredients are mixed and compressed under high pressure and cured at room temperature. They can be produced in under 24 hours. The flyash in the bricks increases the strength of the bricks in the later stages.
Advantages Of Fly Ash Bricks:
i) Clay is a precious mineral on the earth. The use of clay is replaced with fly ash – a waste product of the coal industry.
ii) Fly ash bricks are more resistant to freeze thaw cycles.
iii) They have higher compressive strength of 30 N/mm2.
iv) It reduces mercury pollution.
v) It saves 20% of the cost.
vi) It can be produced in 24 hours.
vii) It has low water absorption percentage than clay bricks.
viii) They are light in weight and thus reduce the cost of the foundation.
ix) Unlike clay bricks, they do not require soaking in water before usage.
Disadvantages Of Fly Ash Bricks:
i) Not all fly ash is compatible with the concrete.
ii) The bonding may be less due to the smooth finishes.
5. Fire Bricks:
Fire bricks are made of silica (65% to 75%) and alumina (25% to 35%). The high amount of alumina present in the bricks allows it to perform well under high temperatures. Other impurities like magnesium, calcium and iron are limited to less than 5%. The bricks are baked at 1600 to 1900 degrees in a continuous kiln and allowed to cool down naturally. This type of bricks can be made of clay, silica, bauxite, chromite, or magnesite.
i) Low thermal coefficient of expansion of the bricks helps to withstand high temperatures.
ii) It has high strength and resistance for palling.
iii) It can be used in chimneys, boilers, kilns and furnaces.
i) They are costly.
ii) They have high water absorption capacity
iii) They have very less tensile strength and cannot be used in seismic zones.
6. Engineering Bricks:
Engineering bricks are the special types of bricks that have high compressive strength and low porosity. Engineering bricks are classified into Type A bricks and Type B bricks.
The Type A bricks have a minimum compressive strength of 125 N/mm2 and maximum water absorption of 4.5%.
The Type B bricks have a minimum compressive strength of 75 N/mm2 and maximum water absorption of 7%. Type B bricks are used widely.
Advantages Of Engineering Bricks:
i) They can be used in cold weather regions due to low porosity and resistance to freeze thaw cycles.
ii) They can be used in underground construction where there is seepage of water due to its low permeability.
Disadvantages Of Engineering Bricks:
i) They don’t produce a pleasing appearance hence they can be used for underground works like sewers, tunnels and manholes.
ii) They are costly.