Efflorescence of brunt clay Bricks

When the brick earth contains an excess amount of alkaline salts, after absorbing moisture from the atmosphere and on drying it leaves a greenish white deposit on the surface of the brick. The Efflorescence test is performed as per IS 3495 Part 3 to know the presence of alkaline matter in the bricks using a shallow flat bottom dish containing sufficient distilled water to completely saturate the brick.

Procedure:

1. Take the sample as per IS 5454, for a brick lot of 2001 to 10000, 5 bricks are taken as sample.
2. Place the end of the brick in the dish, the depth if the immersion being not less than 25 mm.
3. Place the whole arrangement in a warm $(\text{20 to 30}^\circ {C})$ well ventilated room untill all the water in the dish is absorbed by the brick, cover the whole arrangement with suitable glass cylinder to arrest the excess evaporation of water.
4. When all the water has been abosorbed and the brick appears to be dry, place a smiliar quantity of water in the dish and allow it to evaporate as before.
5. Examine the brick after the second evaporation and report the results.

The liability to efflorescence is recoreded in-accordance with the following standards:

Liability	Definition
Nil	When there is no perceptible deposit of efflorescence.
Slight	When not more than 10% of the exposed area of the brick is covered with a thin deposit of salts
Moderate	When there is a heavier deposit than under "slight" covering up to 50% of the exposed area of the brick surface but unaccompanied by powdering or flaking of the surface.
Heavy	When there is a heavy deposit of salts covering 50% or more of the exposed area of the brick surface but unaccompanied by powdering or flaking of the surface.
Serious	When there is a heavy deposit of salts accompanied by powdering and/or flaking of the exposed surface.

The rating of efflorescence shall not be more than "moderate" upto class 12.5 and "slight" for higher classes.

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Water Absorption Test of burnt Clay Brick

Water absorption test is a very important test as it is testing the porosity of a brick. The more porous the brick, the more will be the absorption and the less will be the compressive strength.
This test is performed as per IS 3495 Part 2 with the help of an oven and a sensitive balance capable of weighing within 0.1% of the mass of the specimen.

Procedure:

1. Take the sample as per IS 5454, for the lot size in between 2001 and 10000, 5 bricks are taken as the sample. 
2. Dry the bricks in a ventilated oven at a temperature of $105-115^\circ{C}$.
3. Cool the bricks at room temperature and weigh them say, ${W}_{1}$.
4. Immerse the completely dried bricks in clean water at room temperature of $27\pm 2{}^\circ C$ for 24 hours.
5. Remove the bricks from water and wipe out any traces of water with a damp cloth and weigh them, say ${W}_{2}$. 

Water absorption,
$\frac{{W}_{2}-{W}_{1}}{{W}_{1}}\times{100}$
Water absorption should be less than 20% for first class bricks, 22% for second class bricks and 25% for third class bricks.

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Compressive Strength test on brick

Compressive strength test on bricks is performed to know the crushing strength of bricks which should not be less than the specified limit. This test is performed as per IS 3495 part 1.

Procedure:

1. Take 5 bricks from the samples already taken at random.
2. Immersed them in water at room temperature for 24 hours
3. After 24 hours, take them out of the water and wipe off the surplus moisture.
4. Fill the frog and all the voids in the brick with cement mortar 1:1 (1 cement, 1 clean coarse sand of grain in size 3 mm or small)
5. Store the bricks under sacks for 24 hours
6. After the expiry of 24 hours, immerse them in water for 3 days.
7. At the end of 3 days, bricks are taken out and wiped dry and place with flat surface horizontal and the mortar filled face upward between 2 or 3 plywoods sheets, each approximately 3 mm thick and carefully centred between the plates of compression testing machine.
8. The load is applied at a uniform rate of $\text{14 }N/m{{m}^{2}}$ per minute until failure occurs.

                      $\text{Compressive Strength =}\frac{\text{Maximum load at failure}}{\text{average area of the bed face}}$

The compressive strength of any individual brick shall not fall below average compressive strength specified for the corresponding class of bricks by more than 20%. 

Compressive strength of first-class brick and second class brick shall not be less than $10.5 N/{{mm}^{2}}$ and $7.5 N/{{mm}^{2}}$ respectively.

Classification of common burnt bricks on the bases of compressive strength as per IS 1077 

 

Class Designation	Average Compressive Strength, $N/{{mm}^{2}}$
35	35
30	30
25	25
20	20
17.5	17.5
15	15
12.5	12.5
10	10
7.5	7.5
5	5
3.5	3.5

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Test on Bricks

Bricks are tested to know their suitability for the work. For testing samples of bricks are taken and in general 50 bricks are selected for every consignment or stacking of 50,000 bricks.

Sampling of Bricks

1. Sample in Motion: In this method, some samples of bricks shall be taken when bricks are being moved as in the case of loading or unloading at regular intervals so as to get a true representation of the whole quantity.
2. Sampling from a Stack: In  this method, samples shall be taken out at random from a stack of bricks. The number of bricks required for the test shall be selected from the top, the sides accessible and interior of the stack.

Dimensional and Tolerance Test

This test is performed to know the accuracy of the dimensions of the bricks which should be within the specified limits.
To perform this test, 20 bricks out of the sample already taken, are selected at random. All blisters, loose particles of clay and small projections shall be removed.
They shall be arranged upon a level surface in contact with each other and in a straight line according to the dimensions to be measured as shown in figure.
The overall length of the assembled bricks shall be measured accuratly with a steel tape.

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