Theory:
Brick is a very common construction material obtained by moulding clay in rectangular blocks of uniform size and then by drying and burning them at a required temperature. Due to high strength and durability, easy availability and low cost; they are nowadays widely usedfor building construction.
On the basis of their size, IS 1077:1992 classifies bricks into two categories, i.e. modular and non-modular type. The sizes of modular brick are selected in conformity with the metric system considering 100 mm module as the basis of all dimensional standardization. The standard modular sizes of Indian bricks are:
Without mortar : 190 mm × 90 mm × 90 mm
With mortar: 200 mm × 100 mm × 100 mm
However, bricks of non-modular sizes are also available in India, which satisfies other requirements of the code, but not the requirements regarding dimension. The standard sizes of non-modular bricks varies region to region basis. In Odisha the standard size of nonmodular bricks available is 225 mm × 125 mm × 75 mm (without mortar). This size may vary slightly due to drying shrinkage.
To assess the size of the brick, at least twenty numbers of whole bricks is taken at random from the stock. All blisters, loose particles of clay and small projections shall be removed. Then they shall be arranged upon a level surface successively as shown in Figure
10 in contact with each other and in a straight line. The overall length of the assembled bricks shall be measured with a steel tape or other suitable inextensible measure sufficiently long to measure the whole row at one stretch. Measurement by repeated application of short rule or measure shall not be permitted. For a good quality of brick, tolerances in dimensions are allowed within ± 3.0 %.
Bricks used in construction work should have adequate compressive strength to resist lateral and vertical loads. Ordinary bricks are designated on the basis of average compressive strength as follows:
The compressive strength of any individual brick tested shall not fall below the minimum compressive strength specified for the corresponding class of brick. To access the compressive strength of the bricks, load is applied over the flat side keeping mortar filled face facing upwards.
Water absorption of a brick is defined as the ratio of weight of water absorbed to the dry weight of the unit under a given method of treatment in a standard period of time. Water absorption indicates degree of porosity in a brick. Strength, stiffness, unit weight and other properties decrease with porosity. For good quality of bricks, after immersion in cold water for 24 hours, the water absorption should not be more than 20% by weight efflorescence of bricks is usually seen as a white powder (salts of crystallization) caused by water soluble salts as Sulphates of Calcium, Magnesium, Sodium, Potassium etc. and Sodium Chloride. These salts are deposited on the surface of the bricks on the evaporation of water. Efflorescence decreases strength and stiffness of bricks. The liability to efflorescence is reported as ‘nil’, ‘slight’, ‘moderate’, ‘heavy’ or ‘serious’ in accordance with the following definitions:
Objective:
To estimate dimension, tolerance, compressive strength, water absorption, and efflorescence of bricks.
Reference:
IS 3495 (Part-1 to 4):1992.
Apparatus:
(1) Dimensions and tolerance: Measuring tape, trowel and brush.
(2) Water absorption: Weighing balance, metal tray about 5 cm deep, ovens.
(3) Compressive strength: Compression testing machine
(4) Efflorescence: A shallow flat bottom dish or tray.
Material:
(1) Dimensions and tolerance: Bricks (20 nos.)
(1) Water absorption: Bricks and water.
(2) Compressive strength: Bricks, cement, sand, water and two 3 mm thick plywood sheets.
(3) Efflorescence: Bricks and water.
Procedure:
For dimension and tolerance test:
1. Collect at least twenty numbers of whole bricks at random from the stock.
2. Remove all blisters, loose particles of clay and small projections from the
surface of the brick.
3.Arrange the bricks upon a level surface successively as shown in Figure 1 in
contact with each other and in a straight line.
4. Measure the overall length of the assembled bricks with the steel tape.
Measurement by repeated application of short rule or measure shall not be
permitted. If, for any reason it is found impracticable to measure bricks in one
row, then divide the samples into rows of 10 bricks each and measure them separately to the nearest millimetre. Then, add all these dimensions together.
For water absorption test:
5. Dry the specimen in a ventilated oven at a temperature of 105 to 115o C for 24
hours. Then cool it to the room temperature and determine its weight (W1).
6. Immerse the dried specimen completely in clean water at a temperature of 27 ±2 o C for 24 hours. Then remove the specimen, wiped of any traces of water and measure its weight (W2). This weighing shall be completed within three minutes after the specimen has been removed from water. Determine percentage of water absorption.
For compressive strength test:
7. Remove the unevenness observed in the bed faces to provide two smooth and
parallel faces by grinding. Immerse in water at room temperature for 24 hours.
Remove the specimen and drain out any surplus moisture at room temperature.
8. Fill the frog and all voids in the bed face flush with cement mortar having
cement sand ratio 1:3.
9. Store under damp gunny bags for 24 hours followed by immersion in water for
3 days. Remove the bricks and wipe out traces of moisture.
10. Place the specimen with mortar filled face upward, between two 3 mm thick plywood sheets, carefully centred between platens of the testing machine.
Apply load axially at a uniform rate of 14 N/mm2/min and note the maximum
load at failure. Find compressive stress after dividing total load (in N) by loaded surface area (mm2) For efflorescence test:
11. Place the end of the brick in the disk or tray. The depth of immersion in water
shall be 25 mm.
12. Keep the whole arrangement at a temperature 20oC to 30oC until all the water in the dish is absorbed by the specimens and the surplus water evaporates.
13. When the water has been evaporated and the bricks appear to be dry, place a
similar quantity of water in the dish and allow it to dry evaporate as before.
14. Examine the bricks for efflorescence after the second evaporation and report the results as the definition given in Table 3.
Observations:
Table 1: Observations on dimension and tolerance
Nos. of bricks tested : ________
Standard sizes of bricks taken: ______ mm × ______ mm × ______ mm.
Table 4: Observations on efflorescence test
The percentage of area where efflorescence occurred is : ________ %. Thus the degree of efflorescence is ___________.
Note: Carefully observe the brick that have undergone efflorescence test. And estimate the
percentage of efflorescence area.
Calculation:
• The dimensions of given bricks are : ______ mm × ______ mm × ______ mm
• Compressive strength for the brick specimen is: __________ N/mm2
• Percentage of water absorption for the brick specimen is : ________ % by weight.
• Degree of efflorescence for the brick specimen is found: __________
Conclusions:
• The given bricks has dimensions ______ mm × ______ mm × ______ mm and the
tolerances in dimensions are bellow/ above 3.0%. Thus the bricks are of good quality/ are not of good quality.
• The lowest compressive strength observed by the bricks specimen is __________ N/mm2
. Thus, the brick belongs to _______ class.
• The percentage of water absorption for the brick specimen is less than/ more than 20% by weight. Thus, bricks are of good quality/ are not of good quality.
• The rating of efflorescence for the brick specimen is _______. This is acceptable/
not acceptable for good quality of bricks.
Precautions: (Discuss about the precautions to be taken while conducting this experiment)
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Questions:
1. What are the characteristics of good bricks?
2. What is efflorescence in bricks? What are its causes and remedies?
3. What are the limits for water absorption and compressive strength for various classes of bricks?
4. Why frog filling is necessary for testing of compressive strength?
5. Describe various field tests performed to check the quality of bricks.
