Bricks are of the rectangular shape made up of clay-like block structure. It is used in wall and pavement purposes.
Composition of Brick
Alumina – 20-30%
Lime – 4-5%
Oxides of iron – 5-6%
- It imparts plasticity to brick earth so that it can be easily moulded into any desired shape.
- If it is in excess, it causes shrinkage and warping during dring of bricks and makes bricks too hard during the burning process.
- It prevents cracking, shrinkage and wrapping of bricks. Thereby it imparts uniform shape on it.
- It destroys cohesion between the particles when it is in excess amount. Hence bricks become too brittle.
- Lime also prevents the shrinkage of bricks.
- If it is in excess, it causes the bricks to melt during its burning. Thereby it results in a loss in the shape of bricks.
- During the burning of bricks, calcium carbonate is converted in quick time that undergoes slaking process, which in turn results in the cracking and disintegration of brick due to its increase in volume.
Oxides of iron
- Oxides of iron help lime and silica to react with each other hence leads to the development of strength in the bricks.
- It also imparts reddish colour to the brick.
- It also prevents the shrinkage in brick.
- It imparts yellow tint in bricks.
Harmful ingredients present in bricks
Lime – slaking leads to disfiguration and expansion of bricks.
Iron pyrites – Presence of iron pyrites leads to crystallization and disfiguration of bricks during burning due to the oxidation of these pyrites compound.
Alkalies– Alkali acts as a flux during the burning of the bricks. If it is in excess, it causes the bricks to fire with others, thereby resulting in its twisting and warping. Presence of alkali also leads to efflorescence and staining in bricks.
Stones and pebbles– Presence of stones and pebbles in brick earth lead to the formation of weak and porous bricks. Load carrying capacity which is reduced.
Organic matter/Vegetative matter– Presence of organic and vegetative matter supports in the burning of bricks but if they are left unburnt it reacts with other and results in the formation of gases during their decomposition, which when escaping from the body of bricks leads to the development of numerous voids which result in the decrease of the load-carrying capacity of bricks.
Manufacturing of bricks
Manufacturing of bricks is carried out in 4 distinct operations.
1.Formation of clay
Clay for the brick is formed in the following sequence
- Unsoiling –It is the process in which top 200mm of soil is thrown and is not used for manufacturing of bricks as it consists of the majority of impurities in bricks.
- Digging– It is the process in which soil is dug out and spread over level field to prepare it for the next operation of cleaning.
- Cleaning– It is the process in which impurities like stone, pebbles, organic matter, the vegetative matter is removed from bricks earth manually.
- Weathering– After cleaning the clay, it is exposed to the atmosphere a few weeks or few months for its softening/mellowing or weathering by absorption of moisture.
- Blending– It is the process in which different ingredient of brick is spread over weathered clay in definite proportion.
- Tempering– It is the process in which the required degree of hardness used in the brick earth to make it suitable for new operation of moulding. Tempering of brick earth is done in a pug mill.
- Shape and size of bricks.
- Mould either of wood/steel.
- It can also be done by machine.
- Frog mark is left on the brick up to 10-12mm depth.
Hand moulded bricks are of two types
- Ground moulded
- Table moulded
Quality of table moulded is greater than ground moulded. Table moulding is speed/higher than ground moulding.
Machine moulded bricks are of two types:-
- Plastic clay moulded bricks.
- Dry clay moulded bricks (better quality).
- Without drying, bricks are cracked due to excessive shrinkage.
- Moisture content reduced up to 2%.
- For speedup, drying bricks are placed along their edge.
- Strength and hardness.
- Dense and durable.
- Overburnt becomes brittle and breaks easily and underburnt become soft does not carry loads.
- At 1100 degree Celsius.
- It is done in clamps or kiln.
- In order to prepare clamp, a piece of levelled ground is selected that is trapezoidal in shape.
- The shorter side of trapezoid is constructed in excavation and the longer side is raised by an angle of approximately 15 degrees.
- A brick wall in mud is constructed along shorter side and fuel having a thickness of approximately 700-800mm is spread the over-levelled field.
- Fuel used for burning of bricks in clamp constitutes grass, rice husk, ash, wood, coal dust, cow dunk etc.
- When the clamp is constructed it is covered with the logo of mud in order to avoid the escape of heat from it.
- Burning of bricks takes 2-3 months followed by cooling duration.
- No supervision is required.
- It is economical.
- Bricks are not of uniform quality.
- The trapezoidal plan helps in effective distribution of exhaust gases.
- The inclination of 15 degrees is used to avoid displacement of brick during placing.
Kilns are large-sized oven used for the burning of brick. supply of bricks from this kiln is either continuous or intermittent.
- Continuous kiln– loading, burning, cooling, unloading simultaneously.
- Bull trench kiln
- Hoffman kiln
- Tunnel kiln
- Intermittent kiln– Loading, burning, cooling, unloading sequential.
- Up- drought kiln
- Down-drought kiln
The standard size of brick- 19cm*9cm*9cm
Conventional size- 25cm*11.4cm*7.6cm
- The longer face of the brick is termed as a stretcher.
- The shorter face of the brick is termed as a header.
- The portion of brick cut along its length is termed as closer.
- Queen closer(half)
- Queen closer(quarter)
- King closer
- Bevelled closer
- Mitred closer
- It is the portion of brick cut along its width.
- Half bat
- Bevelled bat
- Three- quarter bat
- It is the exterior angle at the face of the wall. i.e greater than 90 degrees.
Different type of bonding in brick masonry
- An alternate layer of header stretcher.
- Queen closer is placed next to quoin not at the end.
- Alternate stretcher and header placed next to each other.
- Queen closer is placed next to quoin. The header in each alternate course.
- English bond strength > Flemish bond strength.
- It is more economical than the English bond.
- The stretcher is laid by the bricks.
- The half-bat is used in each alternate course.
- Bricks are laid by header in each course.
- Three-quarter bats are used in each alternate course.