TESTS FOR BRICKS

TESTS FOR BRICKS

The tests to be made on bricks are as follows:

1.  Compressive strength

2.  Water absorption

3.  Efflorescence

4.  Dimensional tolerance

5.  Hardness

6.  Soundness.

7.  Structure

We will now deal with the above -mentioned tests.

1.  Compressive strength. Five bricks are taken at random and their dimensions are measured to 1 mm accuracy. They are, then, immersed in water of 25°C to 29°C for 24 hours. The surplus moisture is allowed to drain and the frog. if any. is filled with mortar 1:3 (1 cement, 3 clean coarse sand 3 mm and down). It is kept under a jute bag for another 24 hours after which it is immersed in clean water for three days. At the time of testing, these bricks are removed from water, wiped dry of any trace of moisture and placed with the flat surface horizontal and mortar- filled face up between three plywood sheets each of 3 mm thickness (plaster of Paris may also be used to ensure uniform surface).

The load is applied at the rate of 140 kg/cm 2 per minute till the failure of the specimen takes place as indicated by the needle of the testing machine turning back. Average of the five test values is reported. While finding the average, any single value obtained as compressive strength which is higher than the upper value of the class of the bricks tested, should be taken only as the upper limit of the class. Values less than 20% below the average value should be discarded. The average value should not be less than the specified value.

2.Water absorption. Five bricks are taken for test. They are allowed to dry in an oven at 110' to 115° C till they attain a constant weight which usually takes place in 48 hours. They are then allowed to cool at room temperature, which generally takes 4 to 6 hours without a fan and 2 to 3 hours with a fan blowing on it and weight W1 is measured.

They are then kept in clear water at 27 + 2°C for 24 hours and then wiped dry with a damp cloth and weight W) is measured. The average percentage of water absorbed as percentage of dry weight is reported. Average of the five tests is reported. 

3.   Efflorescence. This test should he conducted in a well -ventilated room at 18-30°C. Average value on five samples taken at random is to he reported. The brick is placed vertically in a dish 30 cm x 20 cm approximately in size with 2.5 cm immersed in distilled water. The whole water is allowed to be absorbed by the brick and evaporated through it. After the bricks appear dry, a similar quantity of water is placed in the dish, and the water is allowed to evaporate as before. The brick is to be examined after the second evaporation and reported as follows:

 a)       Nil. When there is no perceptible deposit of salt.

 b)      Slight. When not more than 10 per cent of the area of brick is covered with salt.

c)    Moderate. When there is heavy deposit covering up to 50% of the area of the brick but unaccompanied by powdering or flaking of the surface.

d)    Heavy. When there is heavy deposit covering more than 50% of the area of the brick accompanied by powdering or flaking of the surface.

e)    Serious. When there is a heavy deposit of salts accompanied by powdering and/or flaking of the surface and this deposition tends to increase in the repeated wetting of the specimen.

Bricks for general construction should not have more than slight -to –moderate efflorescence.

4.      Dimensional tolerance. Twenty whole bricks are selected at random to check measurement of length, width, height, etc. These dimensions are to be measured in one or two lots of ten each as shown in Fig. 2.2. Variations in dimensions are allowed only within narrow limits, ±3 % for class one and ±8% for other classes.

5.Hardness. A scratch is made on the surface of the brick with the finger nail. In a good brick, no impression will be left on the surface.