TESTS ON BRICKS

Before recommending bricks for construction work, their suitability is to be assessed by conducting the following tests:

1. Compressive Strength Test
2. Water Absorption Test
3. Efflorescence Test
4. Dimensional Tolerance Test
5. Hardness Test
6. Soundness Test
7. Structure Test

The sampling and testing of bricks are carried out as per IS: 3495 – 1992 and are as shown in Table 3.2.

Table 3.2 Sampling and testing of bricks

Source: IS: 3495–1992.

3.7.1 Compressive Strength Test

As per norms, five bricks are taken at random and their dimensions are measured accurately to 1 mm. They are immersed in water at 25–29°C for a period of 24 hours. After that they are taken out, and excess moisture is allowed to drain. If the bricks have frogs they are filled with C.M 1:3. They are again kept under a jute bag for another 24 hours. They are again immersed in clean water for three days.

Just at the time of testing they are taken out, one at a time, from the water and wiped dry. The horizontal and mortar-filled surface is placed facing upwards with three thin plywood sheets on a brick-testing machine.

Load is applied on the brick at a rate of 140 kg/cm² per minute till the failure of the brick. An average of five test values of bricks is reported. While computing the average value, any single value obtained as compressive strength which is higher than the upper value of the class of the bricks tested should be taken only as the upper limit of the class. Test values less than 20% of the average should be rejected. Also the average value should not be less than the specified value of the class of the brick.

3.7.2 Water Absorption Test

For the test, five bricks are taken at random from the lot. They are dried in an oven at 110–115°C till they attain constant weight. Generally it takes 48 hours. Bricks are then cooled at room temperature, which generally takes 4–6 hours and are then weighed. Let the weight of a dry brick be W₁.

Bricks are then kept in clean water at 27 ± 2°C for 24 hours. They are taken out, wiped dry with a damp cloth, and the wet weight W₂ is noted.

The average percentage of water absorbed as a percentage of dry weight is reported. This value should not be more than the standard value of a particular class of brick.

3.7.3 Efflorescence Test

The presence of soluble salts causes efflorescence on the surface of the brick. Here also five test samples of bricks are taken at random. The brick is placed in a dish with 2.5 cm immersed in distilled water. The brick is allowed to absorb the water fully, and then the water evaporates through it. When the brick has dried, an additional and equal quantity of water is placed in the dish. As before the water is allowed to evaporate. After the second evaporation, the brick is examined and evaporated as under:

For general construction, bricks should not have more than slight to moderate efflorescence.

3.7.4 Dimensional Tolerance Test

Twenty bricks are taken at random and their dimensions, length, width and depth are measured. Variations in dimensions generally allowed up to ± 3% for class one and ± 8% for other classes.

3.7.5 Hardness Test

The hardness of a brick surface is determined by making a scratch on the surface of a brick with the help of a finger nail. If no impression is left on the surface of the brick, the brick is considered to be hard.

3.7.6 Soundness Test

Two bricks are struck against each other slightly. A good brick has a clear ringing sound, and the bricks should not get break.

3.7.7 Structure Test

In this test a brick is broken, and the broken surfaces are examined for the structure. It should be uniformly burnt, homogeneous in structure, compact and free from any defects such as holes, lumps, etc.