Bricks are extensively used as building material in most of the construction work. The quality of a structure or building is therefore dependent upon the quality of bricks used there in.
We cannot test each and every brick to inspect its quality as it is impractical. That is why a sampling method or procedure must be adopted for proper and objective evaluation of the quality of bricks.
What the term ‘sample’ means?
A sample of bricks means, collection of bricks selected for inspection and/or testing from a lot to reach the decision regarding the acceptance or rejection of the lot.
What is ‘Sampling’?
It is a procedure adopted to collect bricks in such a way that it represents the whole mass.
How sampling is done for bricks?
Sampling of bricks can be done
- At the time of loading or unloading
- From the stack of bricks
- From brick loaded trucks
Whatever the situation may be, the idea is, to divide the whole lot or stack or truck into 10 number of real or imaginary sections and to draw the required number of bricks from each section
Note: While Sampling from stack, remove the bricks from upper layer, so as to sample from places within the stack.
Inspections done on brick samples is two types
- Inspection of visual and dimensional characteristics
- Inspection for physical characteristic
Inspection for Visual and Dimensional Characteristics
The no of bricks to be selected for visual and dimensional characteristics is as per the table-1 given below.
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Table-1 |
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No of bricks in the lot |
For characteristics specified for individual brick |
For dimensional characteristics specified for group of 20 bricks |
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|
No of bricks to be selected |
Permissible no of defectives in the sample |
No of bricks to be selected |
No group of 20 bricks should fail in dimension characteristics |
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|
2001-10000 |
20 |
1 |
40 |
|
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10001-35000 |
32 |
2 |
60 |
|
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35001-50000 |
50 |
3 |
80 |
|
Criteria for acceptance of lot for visual and dimensional 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-1, the lot shall be considered as satisfying the requirements of the visual characteristics.
Note: Remember this criteria is applicable where characteristic is specified for individual bricks.
In case the dimensions and tolerances for bricks are specified for a group of 20 bricks, then number of bricks to be sampled and permissible no of defectives(i.e. criteria for acceptance) is as per specified in col 4 and 5, respectively.
Inspection for Physical Characteristics
If the lot qualifies for visual and dimensional characteristics as stated above, then the next step is to check for the physical characteristics. For this purpose the bricks shall be taken at random from those already selected in as Table-1. Number of bricks to be selected is as per table shown below.
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Table-2 |
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Lot Size |
Sample to be taken for testing of physical characteristics |
Permissible number of defectives for efflorescence |
Warpage |
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Sample Size |
Permissible number of defectives |
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2001-10000 |
5 |
0 |
10 |
0 |
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10001-35000 |
10 |
0 |
20 |
1 |
|
35001-50000 |
15 |
1 |
30 |
2 |
Note: Physical characteristics of bricks means, its compressive strength, breaking load, transverse strength, bulk density, water absorption and efflorescence etc.
Criteria for acceptance of lot for Physical Characteristics
A lot is considered to satisfy the requirements of physical characteristics if
- The average value of all the strength tests (i.e. compressive strength, breaking load and transverse strength) satisfy the requirement specified as per respective standards for various bricks. (Note: if the test result for compressive strength exceeds the upper limit for the class of brick, then the same shall be limited to upper of the class, for the purpose of averaging)
- If compressive strength test is done on individual bricks, then the minimum value should not fall below 20% of the upper limit for the class of brick.
- For water absorption and bulk density, calculate the average value and compare it with specified value as per respective standards for various bricks.
- For efflorescence the permissible number of defectives should not be more than as stated in Table-2.
- For warpage the permissible no of defectives should not be more than as stated in Table-2.