15.1 General
Samples from fresh concrete shall be taken as per IS 1199 and cubes shall be made, cured and tested at 28 days in accordance with IS 516.
15.1.1
In order to get a relatively quicker idea of the quality of concrete, optional tests on beams for modulus of rupture at 72 ± 2 h or at 7 days, or compressive strength tests at 7 days may be carried out in addition to 28 days compressive strength test. For this purpose the values should be arrived at based on actual testing. In all cases, the 28 days compressive strength specified in Table 2 shall alone be the criterion for acceptance or rejection of the concrete.
15.2 Frequency of Sampling
15.2.1 Sampling Procedure
A random sampling procedure shall be adopted to ensure that each concrete batch shall have a reasonable chance of being tested that is, the sampling should be spread over the entire period of concreting and cover all mixing units.
15.2.2 Frequency
The minimum frequency of sampling of concrete of each grade shall be in accordance with the following:
| Quantity of Concrete in the Work, m³ | Number of Samples |
|---|---|
| 1 - 5 | 1 |
| 6 - 15 | 2 |
| 16 - 30 | 3 |
| 31 - 50 | 4 |
| 51 and above | 4 plus one additional sample for each additional 50 m³ or part thereof |
| NOTE—At least one sample shall be taken from each shift. Where concrete is produced at continuous production unit, such as ready-mixed concrete plant, frequency of sampling may be agreed upon mutually by suppliers and purchasers. | |
15.3 Test Specimen
Three test specimens shall be made for each sample
for testing at 28 days. Additional samples may be required for various purposes such as to determine the strength of concrete at 7 days or at the time of striking the formwork, or to determine the duration of curing, or to check the testing error. Additional samples may also be required for testing samples cured by accelerated methods as described in IS 9103. The specimen shall be tested as described in IS 516.
15.4 Test Results of Sample
The test results of the sample shall be the average of the strength of three specimens. The individual variation should not be more than ±15 percent of the average. If more, the test results of the sample are invalid.