Tests on Bricks

TESTS ON BRICKS

To know the quality of bricks following tests can be performed. In these tests some are performed in laboratory and the rest are on field.

❖ Compressive strength test

❖ Water Absorption test

❖ Size, Shape and Colour test

❖ Hardness test

❖ Soundness test

❖ Structure test

❖ Efflorescence test

Compressive strength test: This test is conducted in laboratory to calculate the compressive strength of brick. It is also called crushing strength test. Generally 5 specimens of bricks are taken and immersed in water for 24 hours. The frog of the brick is filled with 1:3 cement mortar flush and is placed in wet jute bag for 24 hours. Then the specimen is placed in CTM (Compression testing machine) with 6mm plywood on top and bottom for uniform transferring of load on the specimen. Then axial load is applied uniformly at a rate of 14 N/mm². The ultimate load at which brick is crushed is noted. All five brick specimens are tested one by one and average result is taken as brick's compressive/crushing strength. Then the crushing strength is calculated as follows:

Compressive strength = Crushing load / Area of brick loaded

Water Absorption test: In this lab test brick specimens are weighed in dry condition and are immersed in fresh water for 24 hours. After 24 hours of immersion, specimens are taken out from water and wipe out with cloth. The weight of each specimen in wet condition is noted. The difference in weights is the water absorbed by brick. The percentage of water absorption is then calculated by the ratio of water absorbed to dry weight multiplied by 100. Average of five specimens is taken as the water absorption. Good quality brick doesn't absorb more than 20% water of its own weight.

Size, shape and colour test: A good quality brick should have bright and uniform colour throughout. Their shapes should ideally be rectangular, with well-defined, sharp edges and an even surface. In this test randomly collected 20 bricks are staked along the length, width and height. Then these bricks are measured to verify for sizes as per standard 190 mm × 90 mm × 90 mm. Bricks are closely viewed to check if its edges are sharp and straight and uniform in shape.

Hardness test: In this field test a scratch is made on brick surface with a nail. If that doesn't left any impression on brick then that is good quality brick.

Soundness test: In this simple field test, two bricks are held by both hands and struck with one another. If the bricks give clear metallic ringing sound and don't break then those are good quality bricks.

Structure test: For this test a few bricks are broken and their cross-section is closely observed. The cross-section should be homogeneous, compact and free from defects. If there are any lumps, cracks or holes present on that broken face then that isn't good quality brick

Efflorescence test: To find out the presence of alkalis in bricks this test is performed. The presence of alkalies in bricks is harmful and they form a grey or white layer on brick surface by absorbing moisture. In this test a brick is immersed in fresh water for 24 hours and then it's taken out from water and allowed to dry in shade. If any white/grey layer is not visible on surface it proofs that absence of alkalis in brick. If the white/grey patch is visible about 10% of brick surface then the presence of alkalis is in the acceptable range. If white/grey layer is about 50% of surface then it is moderate. If the alkalies presence is over 50% then the brick is severely affected by alkalies.