SOME SIMPLE LABORATORY TESTS OF BRICKS FOR QUALITY CHECK FOR CONSTRUCTION USES

 (a) Water absorption test (as per IS: 3495, Part-2, 1992):

Water absorption value of bricks largely influences the bond between brick and mortar. If water absorption in bricks is more and bricks are not soaked before the masonry work, the water from freshly laid mortar is likely to be absorbed by bricks. This results into poor mortar strength as the sufficient quantity of water will not be available for hydration process. This article describes the details procedure for water absorption test for bricks as per IS 3495 – Part 2.

Apparatus:

1. Sensitive weigh balance

2. Ventilated oven

Procedure:

1. The specimen is dried in a ventilated oven at a temperature of 105 to 115°C; till it attains substantially constant mass. The specimen is cooled to room temperature and its weight is recorded as M1

2. The dried test specimen is immersed completely in clean water at a room temperature of 27±2°C for 24 hours.

3. The specimen is then removed and any traces of water are wiped out with a damp cloth and the specimen is weighed. The weighing is completed 3 min after the specimen has removed from water. Record the weight as M2

Result & Report:

Water absorption, percent by mass, after 24-hour immersion in cold water is given by the following formula:

% water absorption = [(M2-M1) / M1] x 100

Normally, Water absorption shall not be more than 20% by weight up to Brick Class: 12.5 and 15% by weight for higher classes of brick (refer clause: 7.2 of I.S. 1077, 1992)

(b) Determination of efflorescence test of bricks (as per IS: 3495 part 3, 1992)

Efflorescence is a crystalline, salty deposition that occurs on the surfaces of bricks

Apparatus and Materials required

1. Sample of bricks to be tested for efflorescence

2. Distilled water

3. Flat bottom shallow dish made up of glass, porcelain or glazed stoneware having following

details

For square dish : Width = 180 mm , Length = 180 mm , Depth = 40 mm

For circular dish : Dia = 200 mm, Depth = 40 mm

4. Glass cylinder

Procedure

1. Fill distilled water in shallow dish and place the end of the bricks in the dish. Water shall be filled such that bricks should be immersion in water up to 25 mm depth.

2. Place the whole arrangement in a warm well ventilated room until all the water in the dish is absorbed by the specimens and the surplus water evaporates.

3. To avoid excessive evaporation from the dish, cover the dish containing the brick with suitable glass cylinder.

4. When the water has been absorbed and bricks appear to be dry, place a similar quantity of water in the dish and allow it to evaporate as before. Examine the bricks for efflorescence after the second evaporation and report the results.

Result and Report

The results of efflorescence test shall be reported as ‘nil’, ‘slight’, ‘moderate’, ‘heavy’ or

‘serious’:

Nil – When there is no noticeable deposit of efflorescence.

Slight – When thin deposit of salts is covered over exposed area of the brick is less than 10 %

Moderate – When there is a greater deposit than under ‘slight’ and covering up to 50 % of the exposed area of the brick surface but unaccompanied by powdering or flaking of the surface.

Heavy – When there is a heavy deposit of salts covering 50 percent or more of the exposed area of the brick surface but unaccompanied by powdering or flaking of the surface.

Serious – When there is a heavy deposit of salts accompanied by powdering and /or flaking of the exposed surfaces.

But as per Clause 7.3 of IS 1077:1992, the rating of efflorescence shall not be more than “moderate “up to brick class: 12.5 & “Slight” for higher classes.

(C) Compressive strength test of bricks (as per IS: 3495-Part-1-1992)

Objective

For determination of compressive strength of bricks

Apparatus

• Compression Testing Machine

• Steel scale for measuring dimension of brick

Procedure

1. Unevenness observed in the bed faces of bricks is removed to provide two smooth and parallel faces by grinding. It is immersed in water at room temperature for 24h.

2. The specimen is then removed and any surplus moisture is drained out at room temperature. The frog and all voids in the bed face is filled with cement & sand mortar (1 cement: 1 coarse sand of 3 mm down). It is stored under the damp jute bags for 24 h followed by immersion in clean water for 3 days.

3. The specimen is placed with flat faces horizontal, and mortar filled face facing upwards between two 3 ply plywood sheets each of 3 mm thickness and carefully centred between plates of testing machine.

4. Load is applied axially at a uniform rate of 140 kg/cm2 or 14 N/mm2 per minute till failure occurs. The maximum load at failure is noted down. The load at failure is considered the maximum load at which the specimen fails to produce any further increase in the indicator reading on the testing machine.

Calculation

Compressive strength in N/mm2 = (Maximum load at failure in kg or N) / Avg. contact area of the brick in cm2 or mm2.

Reports

Five number of bricks should be tested and the average value is reported.

Minimum compressive strength of bricks are as below:

For 1st Class bricks: 105 kg/cm2

2nd Class bricks: 70 kg/cm2

In any case, common building bricks: Minimum 35 kg/cm2