Various properties of bricks as detailed in the previous article are tested and evaluated according to a set of practice. These tests ( compressive strength of bricks, absorption, efflorescence & size) have been described in detail in relevant codes prepared and published by Bureau of Indian Standards.
In this article, we give only an outline of most important points of these tests.
(1) Compressive Strength of Bricks. (ISS: 1077-1970)
Table of Contents
(i) Take five random bricks samples and immerse them in water for 24 hours at room temperature.
(ii) After 24 hours, take them out, allow them to drain and then clean the surplus water. ‘
(iii) Now, fill their frogs (and any other voids) by a layer of standard 1:1 mortar (1 part cement and 1 part sand). Store these bricks under damp sacks for 24 hours (to allow setting of mortar).
(iv) Place the bricks in water for seven days. (This is to allow the mortar to harden).
(v) Take the bricks out of the water, allow the water to drain and remove the surplus water. When surface dry, each brick is tested for compressive strength individually.
(vi) Place the brick flat-wise, with frog end facing upward, between two plywood sheets.
(vii) Brick so adjusted between the plywood sheets is placed on the bed of compressive strength of bricks testing machine and load is applied axially and at a uniform rate of 140 kg/cm2/minute. (This is very important).
(viii) Note the load at which the brick fails (gets broken). This load (P) is divided by cross-sectional area (A) of the brick gives the compressive strength (Co).
(ix) The arithmetic mean of the compressive strength of bricks values of all the five bricks shall be taken as the compressive strength of that lot of bricks represented by the test samples, (and not for all the bricks of a kiln).
(x) The brick shall be classified accordingly on the basis of the (Co) obtained as above.
Compressive Strength of Bricks.
(i) Compressive Strength of first class brick is 105 kg/cm2.
(ii) Compressive Strength of 2nd class brick is 70 kg/cm2.
(iii) Compressive Strength of common building brick is 35 kg/cm2.
(iv) Compressive Strength of sun dried brick is 15 to 25 kg/cm2.
(2) WATER ABSORPTION TEST (ISS 1077-1970)
(i) Take five whole bricks randomly.
(ii) Dry these samples to a constant weight by placing them in a ventilated oven at 110° C +- 5°C. This may take 48 hours or more time.
(iii) The specimens are weighed individually after cooling.
(iv) The dry, weighed samples are then immersed in water, at room temperature, for 24 hours.
(v) After 24 hours the samples are taken out. Each sample is wiped dry and weighed individually within three minutes after it is taken out from the water.
(vi) Absorption value is calculated by the simple relationship.
Absorption % = w2-w1/w1 x 100
where W1 is dry weight, and W2 is weight after immersion for 24 hours.
(vii) The average of five values for the five samples shall be taken as the water absorption of the brick.
(viii) It shall be within the specified limits for the classification of the bricks.
(3) Efflorescence Test (ISS 1077-1970)
(i) Take five bricks at randomly.
(ii) Place each brick on end in a separate shallow flat bottom dish containing distilled water.
Note that depth of immersion of bricks should not be less than 2.5 cm in each case.
(iii) Keep the above dishes (containing water and bricks) in a warm (18°C to 30°C) room which has adequate Ventilation.
(The water from the dishes will be lost due to absorption by bricks and subsequent evaporation).
(iv) Add fresh quantity of distilled water when the bricks appear having dried.
(v) At the end of the second drying, each brick is observed for efflorescence; that is an appearance of any white patch of salt on the surface of the brick.
The efflorescence is reported only by qualitative words as follows:
Serious. Salt deposition is all round and quite heavy and increases with repeated wetting and drying. Powdering of salt is prominent.
Heavy. Salt deposits cover more than 50 percent of the surface area. The tendency to powder is absent.
Moderate. Salt deposits cover 10-50 percent surface area. The salt forms thin layers without showing any tendency to peal off in flakes or become powdery.
Slight. Salt covers the surface area of less than 10 percent and forms only a very thin sticky layer.
Nil. There is seen no deposit of any salt even after repeated wetting.
It is required that efflorescence should not exceed than the specified degree in various classes of bricks.
For example, in Heavy Duty bricks, it is required to be nil, and for first class bricks, it shall be only slight.
(4) Dimensions Tolerance Test ( ISS 1077-1970).
Objective. The test is performed to check whether the bricks are of required dimensions or not. It is completed in the following manner :
(i) Take twenty bricks at random.
(ii) Remove any loose particles of clay and projecting blisters etc. from the bricks.
(iii) Arrange the bricks on a smooth level surface in a straight series in such a way that the adjoining surfaces are in contact with each other. The arrangement will be done in accordance with the dimension of bricks that is being checked.
Thus, for length, bricks will be laid lengthwise.
For width, bricks are laid on width faces.
For height, bricks are laid on the side.
(iv) The overall length, of the brick rows, is then measured in each case. These shall be within the specified limits for different classes of bricks.
Thus, when the bricks are of standard size (19 x 9 x 9 cm), following limits are specified.
|Class of Bricks||Length (cm)||Width (cm)||Height (cm)|