Tests on Bricks
The following laboratory tests can be conducted on the bricks to find their suitability:
1. Crushing strength
3. Shape and size and
(i) Crushing Strength: Brick specimen is immersed in water for 24 hours. Frog of the brick is filled flush having 1:3 cement mortar and the specimen is hold in damp jute bag for 24 hours and then immersed in clean water for 24 hours. The specimen is placed in compression testing machine having 6 mm plywood on bottom and top of it to get uniform load on the specimen. Then load is applied axially at a regular rate of 14 N/mm2 . The crushing load is noted down. Then the crushing strength is the ratio of crushing load to the area of brick loaded. Average of 5 specimen is taken as the crushing strength.
(ii) Absorption Test: Brick specimen is weighed dry. Then they are immersed in water for a period of 24 hours. The specimen are taken out and then wiped with cloth. Weight of each specimen in wet condition is resolute. The difference in weight show the water absorbed. Then the percentage absorption is the ratio of water absorbed to dry weight multiplied by 100. The average of 5 specimens is taken. This value should not exceed from 20 %.
(iii) Shape and Size: Bricks has standard size and edges should be truly rectangular having sharp edges. To examine it, 20 bricks are selected at random and they are stacked along the width, along the length, and then along the height. For the standard bricks of size 190 mm × 90 mm × 90 mm. IS code allowed the following limits:
Lengthwise: 3680 to 3920 mm
Widthwise: 1740 to 1860 mm
Height wise: 1740 to 1860 mm.
Field tests help in ascertaining the good quality bricks are following:
- Uniformity in color
- Uniformity in size
- Hardness test
- Sound test
- Strength test.
a) Uniformity in Color: A good brick will have uniform color throughout. This observation can be made before purchasing the brick.
b) Uniformity in Size: A good brick should have uniform in size and rectangular plane surface. This verification is made in the field by observation.
c) Hardness Test: For this easy field test is scratching the brick with nail. If no notion is marked on the surface, the brick is adequately hard
d) Structure: A few bricks can be broken in the field and their cross-section observed. The section should be compact, homogeneous and free from defects like lumps and holes.
e) Sound Test: If two bricks are struck with each other they should produce clear ringing sound. The sound should not be dull.
f) Efflorescence: In brick the presence of alkalies is not wanted because they form patches of gray powder by absorbing moisture. so to determine the presence of alkalies this test is performed as described below:
Place the brick specimen in a glass dish having water to a depth of 25 mm in a well ventilated room. After all the water is evaporated or absorbed again add water for a depth of 25 mm. After second evaporation view the bricks for white/grey patches. The observation is reported as which is describe below with meaning
1. Nil: Nil means no patches
2. Slight: it means 10% of area covered with deposits
3. Moderate: it means 10 to 50% area covered with deposit but unaccompanied by flaking of the surface.
4. Heavy: it means more than 50 per cent area covered with deposits but unaccompanied by flaking of the surface.
5. Serious: it means heavy deposits of salt accompanied by flaking of the surface.