- 1 Testing of Bricks
- 2 Defects of Bricks
Testing of Bricks
A brick is taken and it is weighed dry. It is then immersed in water for a period of 16 hours.
Then weigh again and the difference in weights should not, in any case, exceed
(a) 20 percent of the weight of dry brick for first-class bricks.
(b) 22.5 percent for second-class bricks.
(c) 25 percent for third-class bricks.
2. Crushing Strength:
The minimum crushing strength for first-class bricks is 10 N/mm² and for second-class bricks *7.5 N/mm².
In this test, a scratch is made on a brick surface with the help of a finger or nail. If no impression
is left on the surface, the brick is treated to be sufficiently hard.
4. Efflorescence Test
- Efflorescence is characterized by the white powder patches on the surface of the brickwork, brought to the surface, by water and deposited by evaporation.
- To test bricks for efflux, the ends of the brick are placed in a 150 mm diameter porcelain or glass vessel containing a 25 mm depth of water at room temperature (20 °C–30 °C). until all the water is absorbed or evaporated. Water is absorbed or evaporated. The water is then filled into the dish to a depth of 25 mm and allowed to be absorbed or evaporated by the brick.
- The presence of efflorescence is classified as follows:
1. Nil – When the deposit of efflorescence is imperceptible.
2. Slight – When the deposit of efflorescence does not cover more than 10 percent of the exposed area of the brick.
3. Moderate – When the deposit of efflorescence is more than 10 percent but less than 50% of the exposed area of the brick.
4. Heavy – When the deposit of efflorescence is more than 50 percent but the deposits do not powder flake away the brick surface.
5. Serious – When the deposits are heavy and powder or flake away the brick surface.
5. Shape and Size:
- Its shape should be truly rectangular with sharp edges.
- 20 bricks are randomly selected of standard size (19 x 9 x 9 cm). For good-quality bricks, the results should be within the following permissible limits:
Length – 368 cm to 392 cm Width – 174 cm to 186 cm; Height– 174 to 186 cm
- In this test, two bricks are taken and they are struck with each other.
- Bricks should not break and a clear ringing sound should be produced.
- It should be homogeneous, compact, and free from any defects such as holes, lumps, etc.
- High-duty fireclays can resist temperature range of 1482°C to 1648°C; medium-duty fireclay can resist a temperature range of 1315°C to 1482°C and low-duty fireclays can resist temperatures up to 870°C only.
Defects of Bricks
(i) Over Burning of Bricks
- If the bricks are overburnt, a soft molten mass is produced and the bricks loose their shape. Such bricks are not used for construction works.
(ii) Under-Burning of Bricks
- When bricks are not burnt properly, the clay is not softened because of insufficient heat, and the pores are not closed.
- This results in a higher degree of water absorption and less compressive strength.
- Such bricks are not recommended for construction work.
- This defect is observed as a spongy swollen mass over the surface of burnt bricks.
- It is caused due to the presence of excess carbonaceous meter and sulphur in brick clay
(iv) Black Core
- When brick-clay contains bituminous matter or carbon and they are not completely removed by oxidation, the bricks result in a black core mainly because of improper burning.
- This is caused because of alkalis present in bricks.
- When bricks come in contact with moisture, water is obtained and the alkalis crystallize.
- After drying, spots of brown or white powder appear on the surface of the brick. This can be mitigated by selecting the proper clay material for brick construction, preventing moisture from coming into contact with the masonry, providing waterproof coping and using water-repellent materials in the mortar, and providing a damp-proof course.
- .Deformation of the shape of the bricks caused by the rainwater falling on hot bricks is known as chuffs
(vii) Checks or Cracks
- This is because of lumps of lime or excess water.
- In the case of lime, when bricks come in contact with water, the absorbed water reacts with lime nodules causing expansion and consequent disintegration of bricks, whereas shrinkage and burning cracks result when an excess of water is added during brick manufacturing.
- it sulphide, is present in the brick clay and causes dark surface spots on the brick surfaces. Such bricks are not only harmful but also unsuitable for exposed masonry work.
- Broken busters are generally caused on the surface of sewer pipes and drain tiles due to air imprisoned during their moulding.
- It is by the entrapped air in the voids of clay.
- Lamination produces thin lamina on the brick faces which weathers out on exposure.
- Such bricks are weak in structure.