Constituents of Brick | Qualities Of a Good Brick | How To Check Quality Of Brick At Site?

Brick is the most essential and commonly used building material. 

They are commonly being used for constructing walls, columns, roofs, paving floors, etc. Because of their features like easily available, economical, strong, durable, reliable, resistance to atmospheric effects, etc., they are the most commonly used building material.

 

Constituents of brick earth

Good quality bricks cannot be made from every type of clay. Constituents of good brick earth with their compositions and functions are described below:

1.    Alumina (20-30% by weight)

·       It is the main constituent of every kind of brick earth.

·       The alumina content is responsible for providing the plastic character to the clay in wet conditions which makes the process of moulding easy.

If alumina content is more than 30%, then the bricks become more plastic and shrink on drying. But if alumina is less than 20%, then clay might be difficult to mould to desired shapes.

2.    Silica (35-50% by weight)

·       It exists in brick earth either in chemical composition with alumina as silicate of alumina or mechanically mixed with clay as sand.

·       Silica when added to suitable proportion to clay imparts hardness to the brick and checks its shrinkage, cracking, and warping on drying. But if added in greater proportions makes the brick brittle and porous, as silica destroys the cohesion in clay.

·       Hence, the addition of silica increases hardness, durability, and resistance to heat.

3.    Lime (4-6%)

·       One of the compositions of brick is silica, which melts at very high temperatures. So to melt the silica at the furnace's temperature and make the process quicker, the melting temperature of silica is reduced by using lime.

·       Hence, this component makes the burning of bricks quicker. Lime should not be used more than 4%, if used then it may result in excessive softening of clay on heating causing the loss of shape of a brick.

It should be present in finely divided powder states otherwise the lump on burning may give rise to slaking, which is harmful and may cause the slow disintegration of bricks.

4.    Iron Oxide (4-6%)

·       The iron oxide constituent present in the brick earth acts as a flux, helps grains of silica to melt by lowering the melting temperature of silica (sand).

·       It imparts pleasing red color to the brick. If it exceeds the percentage of 8%, then the brick turns dark blue or black.

5.    Magnesia (<1%)

Small quantities of magnesia in brick earth make the bricks yellowish color and reduces the shrinkage.

But, excess of magnesia leads to the decay of bricks.

 

Qualities of a Good Brick

Ø Size and shape: A good brick should be of uniform shape and should be of standard size. It should also have rectangular plane surfaces with parallel sides and sharp straight right-angled edges.

The standard size of the brick is 190mm*90mm*90mm and the depth of the frog should be between 10 to 20mm and the length and width of the frog should be 100mm and 40mm respectively.

A standard brick weighs nearly 30N.

The surface of brick should not be too smooth otherwise, the motor will not stick to it rather slips out.

Ø Structure: A brick should show a uniform compact and homogeneous structure free from voids when broken into pieces.

Ø Porosity: The brick should not absorb more water more than 20% for first-class brick and 22% for the second class brick of its dry weight when kept immersed for 24 hours.

Ø Hardness: A good brick should be hard enough so that fingernails should not be able to make any impressions on the surface when scratched.

Ø Strength: The crushing strength of brick should not be below 5.5 N/mm^2.

The brick should not break when dropped flat on the hard ground from a height of about 1m.

Ø Efflorescence: A good brick should not contain many alkaline salts, which may cause efflorescence on its surface and decay the brick.

Ø Resistance to fire: A good brick should have adequate resistance to fire.

A good quality brick should be able to resist temperatures up to 1200 degrees Celsius. Bricks to be used for the lining of furnaces should be of special quality known as fire bricks.    

Ø Soundness: The bricks should give a clear metallic sound when struck with each other.

Ø Colour: The color of bricks should be uniform and bright.

 

Tests for quality check of brick at the construction site

It is mandatory to test the brick on site to find out the suitability of a brick for the construction work. Major tests to be carried out are:

ü Water absorption test

The brick whose absorption rate is to be determined is first weighed in its dry condition in a weighing machine.

 It is then immersed in water for a period of 16 hours.

 It is weighed again. The difference in weight showcases the amount of water absorbed by the brick.

The difference in weight should not exceed 20% of the weight of dry brick in any case.

 

ü Compressive strength test

At first, the specimen brick is immersed in water for 24 hours. The frog of the brick is filled flush with 1:3 ratio mortar and the brick is stored under damp jute bags for 24 hours followed by immersion in clean water for three days. The specimen is then placed between the plates of the compression testing machine. Load is applied axially at a uniform rate and maximum load at which the specimen fails is noted for determination of compressive strength of brick given by.

Compressive strength= (maximum load at failure) / loaded area of brick

This compressive strength should be greater than 3.4N/mm^2.

If no testing machine is available, the strength can be roughly measured by throwing a brick from a certain height with free fall. The brick should not break when dropped flat on the hard ground from a height of about 1m.

 

ü Efflorescence Test

If soluble alkaline salts are present in the brick, then it may cause efflorescence on the surface of the brick.

In order to find out the presence of soluble salt in brick, it is immersed in water for 24 hours. It is then taken out and allowed to dry in shade. The absence of grey or white deposits on its surface indicates the absence of soluble salts. If the white deposits cover about 10% surface, the efflorescence is said to be slight and it is considered moderate when the deposits cover about 50% of the surface. When white (or grey) deposits cover more than 50% of the surface the efflorescence becomes heavy as it is considered serious.

ü Structure test

A specimen brick is broken and its structure is inspected. It should be homogeneous, compact, and free from lumps, holes, etc.

The figure shown below is of low quality. Since there are holes when broken.

 

ü Shape and size test

The sides of bricks are measured with the measuring tape and the sides should be around 190mm*90mm*90mm, which is the standard size of a brick.

 

ü Soundness test

When two specimen bricks are made to strike with each other, the bricks should not break and a clear ringing sound should be produced.

 

Important Questions

Q. What is shrinkage in brick?

Ans. Shrinkage in brick is a phenomenon, which occurs during the drying process of brick earth due to loss of moisture content in the brick body by evaporation. Shrinkage may lead to the cracking of brick.

Q. What is efflorescence in bricks?

Ans. Efflorescence in brick is the deposit of white-crystalline salt which forms when water is present in the brick.