The following laboratory tests may be conducted on the bricks to find their suitability:
- Crushing strength
- Shape and size and
The brick specimen are immersed in water for 24 hours. The frog of the brick is filled flush with 1:3 cement mortar and the specimen is stored in damp jute bag for 24 hours and then immersed in clean water for 24 hours. The specimen is placed in compression testing machine with 6 mm plywood on top and bottom of it to get uniform load on the specimen. Then load is applied axially at a uniform rate of 14 N/mm2 . The crushing load is noted. Then the crushing strength is the ratio of crushing load to the area of brick loaded. Average of five specimen is taken as the crushing strength.
Brick specimen are weighed dry. Then they are immersed in water for a period of 24 hours. The specimen are taken out and wiped with cloth. The weight of each specimen in wet condition is determined. The difference in weight indicate the water absorbed. Then the percentage absorption is the ratio of water absorbed to dry weight multiplied by 100. The average of five specimen is taken. This value should not exceed 20 per cent.
Shape and Size:
Bricks should be of standard size and edges should be truely rectangular with sharp edges. To check it, 20 bricks are selected at random and they are stacked along the length, along the width and then along the height. For the standard bricks of size 190 mm × 90 mm × 90 mm.
IS code permits the following limits:
Lengthwise: 3680 to 3920 mm
Widthwise: 1740 to 1860 mm
Heightwise: 1740 to 1860 mm
The following field tests help in acertaining the good quality bricks:
- Uniformity in size
- Uniformity in colour
- Hardness test
- Sound test
- Strength test.
Uniformity in Size:
A good brick should have rectangular plane surface and uniform in size.
This check is made in the field by observation.
Uniformity in Colour:
A good brick will be having uniform colour throughout. This observation may be made before purchasing the brick.
A few bricks may be broken in the field and their cross-section observed. The section should be homogeneous, compact and free from defects such as holes and lumps.
If two bricks are struck with each other they should produce clear ringing sound.
The sound should not be dull.
For this a simple field test is scratch the brick with nail. If no impression is marked on the surface, the brick is sufficiently hard
The presence of alkalies in brick is not desirable because they form patches of gray powder by absorbing moisture. Hence to determine the presence of alkalies this test is performed as explained below:
Place the brick specimen in a glass dish containing water to a depth of 25mm in a well ventilated room. After all the water is absorbed or evaporated again add water for a depth of 25mm. After second evaporation observe the bricks for white/grey patches. The observation is reported as ‘nil’, ‘slight’, ‘moderate’, ‘heavy’ or serious to mean
(a) Nil: No patches
(b) Slight: 10% of area covered with deposits
(c) Moderate: 10 to 50% area covered with deposit but unaccompanied by flaking of the surface.
(d) Heavy: More than 50 per cent area covered with deposits but unaccompanied by flaking of the surface.
(e) Serious: Heavy deposits of salt accompanied by flaking of the surface.