Contd. from Part-A …..
b) Efflorescence test : Conventional clay bricks may contain some amount of alkaline substance in them. However, the greater the presence of such content the greater the risk of efflorescence which appear in the surfaces of bricks as fine whitish layers (deposits). These are hard to control and can lead to other perpetual problems, especially esthetic ones, in a structure.
It is always better to ascertain the quality of bricks beforehand with regard to the efflorescence matter. A simple test as described below can serve the purpose easily.
Five randomly picked clean bricks are placed together on their ends in a pan so that there are gaps among the bricks as well as between the bricks and the outer edges of the pan. Cold distilled water is then poured in the pan such that the depth of water is at least one inch. That is, at least one inch of the bricks must be under water. The pan is then kept under observation in an well-ventilated room at room temperature (27¤C or so). As soon as the entire water in the pan gets exhausted distilled water is poured again exactly as described above and kept as it was until the whole water disappears again due to evaporation and suction by the bricks. The bricks are then examined for efflorescence and appraised as described below:
If no or negligible whitish salty formation is observed, efflorescence is considered as “nil”. Similarly, efflorescence is considered as “slight” if 10% or less of the brick surface only is covered with the salty substance. The same is regarded as “moderate” if 50% of the surface is affected by the whitish salty diposit but without formation of flakes. Efflorescence is considered as “heavy” in case 50% of the surface is affected by whitish powdery diposit simultaneously with flaking of the surface.
For any quality brickwork bricks of “nil” or, at the most, “slight” efflorescence only are adviced. Anything more than that may be used only in low quality work where efflorescence won’t pose as a major issue.
c) Test of compressive strength : Five randomly picked clean & smooth bricks are kept immersed in water for 24 hours at room temp. Thereafter these saturated bricks are taken out and any excess surface water is wiped off. The frogs are then filled with 1 : 1 mortar and smoothened flat with trowel. The frogless bricks are now kept under wet fabric for 24 hrs. Thereafter, they are kept immersed in water for 72 hrs. These are then taken out of water. A thin ply-board is placed on the lower plate of a compressive strength testing machine. One brick is placed on the ply-board with it’s filled frog upwards. Another similar sheet is placed on the top of the brick. Load is now applied on the brick at an uniform rate of 1.4 kg/sq.mm per minute. When the brick fails the reading shown by the needle in the dial is noted down. This is repeated for all of the five bricks. The average of the five readings is calculated and is considered as the compressive strength for the bricks. For any brickwork of good quality the compressive strength should not be less than 50 kg/sq.cm.
d) Dimension test : Detail like tolerances in the dimensions of bricks for this test will depend on the type of brick to be used in a particular work. There are conventional (commonly used) bricks and modular bricks in use for various work. Both have different dimensions. The conventional clay bricks too come in several sizes. Hence, corresponding (specific) requirements may be referred to while conducting dimension test for a particular variety of brick. This is the simplest and the quickest of all the four tests mentioned above.
Did you know : Wienerberger AG of Vienna, Austria is the world’s largest producer of clay bricks. The company has more than 200 plants spread across some 30 countries.