Details about bricks

Quality of good clay Bricks :-

The bricks are table moulded, well burnt in kilns, copper coloured free from cracks and with sharp and square edges.
The bricks should be uniform in shape and should be of standard size.
The bricks should give a clear metallic ringing sound when struck with each other.
The bricks when broken and fractured should show a bright homogenous and uniform compact structure free from voids.
The brick should be sufficiently hard. No impression should be left on brick surface when it is scratched with finger nail.
The bricks should not be pieces when dropped flat hard ground from a height of 1 meter.
The bricks, when soaked in water for 24 hours should not show deposits of white salts when allowed to dry in shade.
No brick should have the crushing strength below 5.50 N/mm2.

1. Absorption :-

A brick is taken and it is weighted dry. It is then immersed in water for a period of 16 hours.
Then weight again and the difference in weight shouldn't, in any case, exceed

a). 20% of weight of dry brick for 1st class bricks.

b). 22.5% for 2nd class bricks.
c). 25% for 3rd class bricks.
2. Crushing Strength :-

Minimum crushing strength for 1st class brick should not less than 10 N/mm2 and for 2nd class bricks should not less than 7.5 N/mm2.

3. Hardness :-

In this test, a scratch is made on brick surface with the help of a finger nail. If no impression is left on the surface, brick is treated to be sufficiently hard.

4. Presence of soluble salt :-

Soluble salt, it present in bricks, will cause efflorescence on the surface of bricks.
It is immersed in water for 24 hours. It is then taken out and allowed to dry in shade. Absence of grey or white deposited on its surface indicates absence of soluble salts.
If the white deposits cover about 10% surface, the efflorescence is said to be slight.
When white deposit cover about 50% of surface then it is said to be moderate.
If grey or white deposits are found to be more than 50% of surface then the efflorescence becomes heavy and it is treated as serious.

5. Shape and Size :-

It's shape should be truly rectangular with sharp edges.
20 bricks are randomly selected for standard size (190×90×90 mm) for good quality bricks.

6. Soundness :-

7. Structure :-

It should be homogeneous, compact and free from any defects such as holes, lumps, etc.
High duty fire clay can resist temperature range of 1482℃ to 1648℃.
Medium duty fire clay can resist temperature range of 1315℃ to 1482℃.
Low duty fire clay can resist temperature range upto 870℃ only.

Composition of good brick :-

1. Alumina = 20 -30 %

2. Silica = 50-60 %

3. Iron oxide = 5-6 %

4. Lime = 2-3 %

5. Magnesia = 1 %

Manufacture of brick :-

1. Preparation of clay :

a. Inspiring

b. Digging

c. Cleaning

d. Weathering

e. Blending

f. Tempering

2. Moulding :

a. Hand moulding

b. Machine moulding

3. Drying ;

4. Burning :

a. Clamps

b. Kilns

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