Test on Bricks

 

Testing Methods For Clay 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

1. Compressive Strength Test -

The crushing strength of a brick is found out by placing it in a compression testing machine. It is pressed till it breaks. As per IS: 1077-1970 the minimum crushing or compressive strength of bricks is 3.50 N/mm2. The bricks with crushing strength of 7 to 14 N/mm² are graded as A.

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(cement mortar) 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 specimen is placed in the compression testing machine (CTM) with flat faces horizontal and mortar filled face being upwards.

Load is applied at a uniform rate of 14 N/m2 per minute till failure. The maximum load at failure divided by the average area of bed face gives the compressive strength.

Compressive strength (N/mm2) = Maximum load at failure (N)/Average area of bed faces (mm2).

Fig: Compressive Strength test for bricks

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.

Percentage water absorption = (W2 - W1) * 100 / W1

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. Efflorescence Test - 

• The presence of soluble salts causes efflorescence on the surface of the brick. 
• Five test samples of bricks are taken at random. 
• The brick is placed in a dish with 2.5 cm immersed in distilled water.

Fig: Efference test of bricks

• The brick is allowed to absorb the water fully, and then the water evaporates through it. In bricks water moves along its pores by capillary action and carries with it dissolved salts.
• 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:

S.No.	Observation	Effect of efflorescence
i.	No perceptible deposit of salt	null
ii.	Not more than 10% of the area of the brick is covered with salt	slight
iii.	Salt deposit covering up to 50% of the area but not powder or flakes	Moderate
iv.	Salt deposit covering more than 50% with powdering or flaking of surface	Heavy
v.	Heavy deposit of salt extremely high accompanied by powdering	Serious

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

4. Dimensional Tolerance Test -

• In this test, collect randomly 20 bricks of standard size.
• Stack these bricks along the lengthwise, measure the length of 20 bricks and note down its length.
• Stack these bricks along the width, measure the width of 20 bricks and note down the measurement.
• Stack these bricks along the height, measure the height of 20 bricks and note down the measurement.

For good quality bricks the results should be within the following permissible limits:

Length: 3720 mm - 3880 mm (or) +/- 80 mm

Width: 1760 mm - 1840 mm (or) +/- 40 mm

Height: 1760 mm - 1840 mm (or) +/- 40 mm

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 fingernail. If no impression is left on the surface of the brick, the brick is considered to be hard.

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.

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.