Test required for Brick /Brick Masonry
A- TEST FOR DIMENSIONAL TOLERANCE
A -1. Sampling
Sampling: For carrying out compressive strength, water absorption, efflorescence and dimensional tests, the samples of bricks shall be taken at random according to the size of lot as given in Table -A.
The sample thus taken shall be stored in a dry place until tests are made. For the purpose of sampling, the following definition shall apply.
(a) Lot: A collection of bricks of same class and size, manufactured under relatively similar conditions of production. For the purpose of sampling a lot shall contain a maximum, of 50,000 bricks.
In case a consignment has bricks more than 50,000 of the same classification and size and manufactured under relatively similar conditions of production, it shall be divided into lots of 50,000 bricks or part thereof.
(b) Sample: A collection of bricks selected for inspection and/or testing from a lot to reach the decision regarding the acceptance or rejection of the lot.
(c) Defective: A brick failing to meet one or more of the specified requirements.
The samples shall be taken as below:
(i) Sampling from a Stack: When it is necessary to take a sample from a stack, the stack shall be divided into a number of real or imaginary sections and the required number of bricks drawn from each section. For this purpose bricks in the upper layers of the stack shall be removed to enable
units to be sampled from places within the stack.
Note: For other methods of sampling i.e. sampling in motion and sampling from lorries or trucks, IS :5454 may be referred.
Scale of sampling and criteria for conformity for visual and dimensional characteristics:—
Visual characteristics: The bricks shall be selected and inspected for ascertaining their conformity to the requirements of the relevant specification.
The number of bricks to be selected from a lot shall depend on the size of lot and shall be in accordance of Col. 1 and 2 of Table - A for visual characteristics in all cases and dimensional characteristics if specified for individual bricks.
(ii) Visual Characteristics: All the bricks selected above in accordance with Col. 1 and 2 of Table -A shall be examined for visual characteristics. If the number of defective bricks found in the sample is
less than or equal to the corresponding number as specified in Col. 3 of Table - A the lot shall be considered as satisfying the requirements of visual characteristics, otherwise the lot shall be deemed as not having met the visual requirements.
(iii) Dimensional Characteristics: The number of bricks to be selected for inspecting the dimensions and tolerance shall be in accordance with Col. 1 and 4 of Table -below . These bricks will be divided into groups of 20 bricks at random and each of the group of 20 bricks thus formed will be tested for all the dimensions and tolerances. A lot shall be considered having found meeting the requirements of dimensions and tolerance if none of the groups of bricks inspected fails to meet the specified requirements
Table - A
Table -B
A -2. ProcedureTable - A
Note: In case the lot contains 2000 or less bricks the sampling shall be as per decision of the Engineer-in-Charge.
(iv) Scale of Sampling and Criteria for Physical Characteristics: The lot which has been found satisfactory in respect of visual and dimensional requirements shall be next tested for physical characteristics like compressive strength, water absorption, efflorescence as specified in relevant material specification. The bricks for this purpose shall be taken at random from those already selected above. The number of bricks to be selected for each of these characteristics shall be in accordance with relevant columns of Table -B.
Table -B
Note: In case the lot contains 2000 or less bricks, the sampling shall be as per decision of Engineer-in-Charge.
(v) A lot shall be considered having satisfied the requirements of physical characteristics if the condition stipulated here in are all satisfied.
(a) From the test results for compressive strength, the average shall be calculated and shall satisfy the requirements specified in relevant material specification.
Note: In case any of the test results for compressive strength exceeds the upper limit for the class of bricks, the same shall be limited to the upper limit of the class for the purpose of averaging.
(b) Wherever specified in the material specification, the compressive strength of any individual bricks tested in the sample shall not fall below the minimum average compressive strength specified for the corresponding class of brick by more than 20 percent.
(c) From the test results for water absorption, the average for the bricks in the sample shall be calculated and shall satisfy the relevant requirements specification in material specification.
(d) The number of bricks failing to satisfy the requirements of the efflorescence specified in the relevant specification should not be more than the permissible no. of defectives given in Col.3 of Table-B.
All the blisters, loose particles of clay and small projections shall be removed from the surface of bricks. Each specimen of 20 bricks shall then be arranged upon a level surface successively as indicated in Fig. A, B and C of para A-4 below in contact with each other and in straight line. The overall length of the assembled bricks (20 Nos) shall be measured with a steel tape sufficiently long to measure the whole row at one stretch.
A-3. Tolerance
The actual dimensions of bricks when tested as described in A-2 shall be within the following limits
per 20 bricks.
A lot shall be considered conforming to the requirements of dimensions and tolerances if all the groups of bricks are tested to meet the specified requirements.
B - TEST FOR COMPRESSIVE STRENGTH
B-1. Specimen
Five whole bricks shall be taken from the samples as specimens for this test. Length and width of each specimen shall be measured correct to 1 mm.
B-2. Apparatus
The apparatus consists of compression testing machine, the compression plate of which shall have a ball seating in the form of portion of a sphere the centre of which shall coincide with the centre
of the plate.
B-3. Procedure
After removal from water, the bricks shall be wiped out of any traces of moisture.
(b) Actual Testing: Specimen shall be placed with flat faces horizontal and mortar filled face upward between three 3 ply plywood sheets each of thickness 3 mm and carefully centred between plates of the testing machine. Plaster of Paris can also be used in place of plywood sheets to ensure a uniform surface.
Load shall be applied carefully axially at uniform rate of 14 N/mm2 per minute till the failure of the specimen occurs.
B-4. Reporting the Test Results
The compressive strength of each specimen shall be calculated in N/mm2 as under :
Compressive Strength ={Maximum load at failure (in N) / Area of Specimen (in sq mm)}
In case the compressive strength of any individual brick tested exceeds the upper limit of the average compressive strength specified for the corresponding class of brick, the same shall be limited to the upper limit of the class specified in table below for the purpose of calculating the average compressive strength. Compressive strength of all the individual bricks comprising the sample shall be averaged and reported.
B-5. Criteria for Conformity
A lot shall be considered having satisfied the requirements of average compressive strength if the average compressive strength specified in Table above for the corresponding class of brick tested is not below the minimum average compressive strength specified for the corresponding class of bricks by more than 20 percent.
C - TEST FOR WATER ABSORPTION
C-1. No. of Specimen
Five whole bricks shall be taken from samples as specimen for this test.
C-2. Apparatus
A balance required for this test shall be sensitive to weigh 0.1 percent of the weight of the specimen.
C-3.Procedure
(a) Pre-conditioning: The specimen shall be allowed to dry in a ventilated oven at a 110°C to 115°C till it attains a substantially constant weight. If the specimen is known to be relatively dry, this would be accomplished in 48 hours, if the specimen is wet, several additional hours may be required to attain a constant weight. It shall be allowed to cool at room temperature. In a ventilated room, properly separated bricks will require four hours for cooling, unless electric fan passes air over them continuously in which case two hours may suffice.
The cooled specimen shall be weigh (W1) a warm specimen shall not be used for this purpose.
(b) Actual Testing: Specimen shall be completely dried before immersion in the water. It shall be kept in clean water at a temperature of 27°C ± 2°C for 24 hours. Specimen shall be wiped out of the traces of water with a damp cloth after removing from the water and then shall be weighed
within three minutes after removing from water (W2).
C-4. Reporting the Test Results
The water absorption of each specimen shall be calculated as follows and the average of five tests shall be reported.
Water Absorption ={ (W2– W1) / W1 } * 100
C-5. Criteria for Conformity
A lot shall be considered having satisfied the requirements of water absorption if the average water absorption is not more than 20% by weight.
D - TEST FOR EFFLORESCENCE
D-1. No. of Specimen
Five whole bricks shall be taken as specimen for this test.
D-2. Apparatus
Apparatus required for this test shall be a shallow flat bottom dish containing distilled water.
D-3. Procedure (actual testing)
The brick shall be placed vertically in the dish with 2.5 cm immersed in the water. The room shall be warm (18ºC to 30ºC) and well ventilated. The bricks should not be removed until it absorbs whole water.
When the whole water is absorbed and the brick appears to be dry, place a similar quantity of water in that dish and allow it to evaporate as before. The brick shall be examined after the second evaporation.
D-4. Reporting the Test Results
The rating to efflorescence in ascending order shall be reported as ‘NIL’, ‘SLIGHT’, ‘MODERATE’,‘HEAVY’ or ‘SERIOUS’ in accordance with the following :
(a) NIL: When there is no perceptible deposit of efflorescence.
(b) SLIGHT: When not more than 10 per cent of the area of the brick is covered with a thin deposit of salts.
(c) MODERATE: When there is heavier deposit and covering upto 50% of the area of the brick surface but unaccompanied by powdering or flaking of the surface.
(d) HEAVY: When there is a heavy deposit of salts covering 50% or more of the brick surface but unaccompanied by powdering or flaking of the surface.
(e) SERIOUS: When there is heavy deposit of salts, accompanied powdering and/or flaking of the surface and tending to increase in the repeated wetting of the specimen.
D-5. Criteria for Conformity
A lot be considered having satisfied the requirements of efflorescence if for 4 out of the specimen of 5 bricks, the rating of efflorescence is not beyond “Moderate”.
Thanks a lot
Mukesh Kumar
Gyan of engineering
Source of Content : CPWD SPECIFICATIONS 2019
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