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TESTING OF BRICKS

Brick is generally subjected to the following tests to find out its suitability for the construction work.

compressive strength, hardness test of brick
Testing of Bricks


1. Compressive Strength test

  • Bricks are often subjected to large compressive stresses. 
  • Compressive stresses of bricks provide basics of comparison of quality of bricks, but it is of little value in determining the strength of the wall, as strength of wall mainly depends on the strength of mortar.
  • Any unevenness observed on the bed faces of brick is removed by grinding to provide two smooth parallel faces.
  • It is then immersed in water at room temperature for 24 hours.
  • The frog and all voids in the bed faces of brick are filled flush with cement mortar (1 cement, 1 clean coarse sand of grade 3mm and down).
  • It is then stored under the damp jute bags for 24 hours followed by immersion in clean water for 3 days.
  •  The specimen is then placed with flat faces horizontal and mortar-filled face facing upwards between plates of the testing machine.
  • Load is then applied axially at a uniform rate of 14 MPa per minute till failure occurs and maximum at failure is noted.
  • Compressive strength is given by 

           Compressive strength=(Maximum load at failure/ loaded area of brick)

  • An average of five results is noted.

2. Water Absorption Test

  • Water absorption of bricks depends on their porosity. Almost all bricks absorb water by capillary action. 
  • But porosity and water absorption do not give a proper indication as to whether brickwork can keep away the rainwater and protect the interior from dampness traveling from outside.
  • Permeability measures the travel of moisture through a brick.
  • Percentage of water absorption gives an indication of compactness which is obtained from burning. (Vitrification in the real sense).
  • Absorption can be broken into two categories (a) Absorption (b) Initial rate of absorption (IRA) 
  • Both are important in selecting the appropriate brick.

a) Absorption

(i) 24 Hour Immersion Coldwater Test 

  • Dry bricks are kept in the oven (110土5°C) till it attains constant mass.
  • After cooling the bricks to room temperature its weight is recorded as W1
  • Now bricks are immersed in water at a temperature of 27° 土 2°C for 24 hours. 
  • Bricks are then taken out of the water and wiped with a damp cloth and weighted as W2

                      Water absorption for 24 hrs (W24)% = \frac{{W2 - W1}}{{W1}} \times 100\%

(ii) 5 Hours Boiling Water Test

  • The weight of the oven-dried bricks (W) is recorded as above. Then the specimen is immersed in the water and heated to boiling in one hour and boiled continuously for five hours, followed by cooling down to 27°±1 2°C by a natural loss of heat within 16–19 hours. Then bricks are taken out of the water and wiped with a damp cloth and the weight is recorded as W3.

                           The water absorption in % = \frac{{W3 - W1}}{{W1}} \times 100\%

  • These two are used to calculate the saturation coefficient by dividing the 24-hour cold-water absorption (W24) by the 5-hour boiling water absorption (W5). The saturation coefficient is used to help predict durability.


b) Initial rate of absorption
  • The initial rate of absorption or suction is the rate of how much water a brick draws in during the first minute after contact with water.
  • The suction has a direct bearing on the bond between brick and mortar.
  • When a brick has high suction, a strong, watertight joint may not be achieved. High suction brick surface to dry should be wetted for three to 24 hours prior to laying to reduce the suction and allow the brick's surface to dry.
  • Very low suction brick should be covered and kept dry on the Jobsite.

Note:
  • Generally, bricks are soaked in water before use in masonry work so that they do not absorb water from cement.
  • Average water absorption shall not be more than 20% by weight up to class 12.5 and 15% by weight for higher classes. 
  • For water absorption less than 5%, the danger of frost action is negligible.

3. Efflorescence Test
  • The ends of the brick are kept in a standard porcelain or glass dish (180 mm * 180mm x 40 mm for square-shaped) depth containing 25 mm depth of water at room temperature (20°~30°C) till the entire water is absorbed or evaporated. The room should be well ventilated.
  • Water is again filled to 25 mm depth in the dish and allowed to be absorbed by the brick or evaporated. Cover the dish with a suitable glass cylinder to avoid excessive evaporation.
  • Bricks are examined after second evaporation and the area of white patches is measured on the brick. 
  • The presence of efflorescence is classified as
  1. Nil Deposit of efflorescence is imperceptible. 
  2. A slight Deposit of efflorescence does not cover more than 10 percent of the exposed area of the brick.
  3. Moderate Deposit of efflorescence is more than 10 percent but less than 50% of the exposed area of the brick.
  4. Heavy Deposit of efflorescence is more than 50 percent but the deposits do not powder or flake away from the brick surface.
  5. Serious Deposits are heavy with powdering or flaking the surface.

Note: The specifications limit the efflorescence to be not more than moderate (10-50%) up to class 12.5 and not more than slight (<10%) for higher classes.


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