Chapter 15Acceptance Criteria

NBC 2016 (SP 7:2016) Volume 1

2016 · PDF page 809

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15.1 Compressive Strength

The concrete shall be deemed to comply with the strength requirements when both the following conditions are met:

a) The mean strength determined from any group of four non-overlapping consecutive test results complies with the appropriate limits in col 2 of Table 11.

b) Any individual test result complies with the appropriate limits in col 3 of Table 11.

15.2 Flexural Strength

When both the following conditions are met, the concrete complies with the specified flexural strength:

a) The mean strength determined from any group of four consecutive test results exceeds the specified characteristic strength by at least $0.3 \, N/mm^{2}$ .

b) The strength determined from any test result is not less than the specified characteristic strength less by $0.3 \, N/mm^{2}$ .

15.3 Quantity of Concrete Represented by Strength Test Results

The quantity of concrete represented by a group of four consecutive test results shall include the batches from which the first and last samples were taken together with all intervening batches.

For the individual test result requirements given in col 3 of Table 11 or in 15.2(b), only the particular batch from which the sample was taken shall be at risk.

Where the mean rate of sampling is not specified the maximum quantity of concrete that four consecutive test results represent shall be limited to $60\mathrm{m}^3$ .

15.4 If the concrete is deemed not to comply pursuant to 15.1 or 15.2 as the case may be, the structural adequacy of the parts affected shall be investigated (see 16) and any consequential action as needed shall be taken.

15.5 Concrete of each grade shall be assessed separately.

15.6 Concrete is liable to be rejected if it is porous or honey-combed, its placing has been interrupted without providing a proper construction joint, the reinforcement has been displaced beyond the tolerances specified, or construction tolerances have not been met. However,

Table 11 Characteristic Compressive Strength Compliance Requirement(Clauses 15.1 and 15.3)
Specified Grade	Mean of the Group of 4 Non-Overlapping Consecutive Test Results	Individual Test Results
	$N/mm^{2}$	$N/mm^{2}$
	Min	Min
(1)	(2)	(3)
M 15 and above	$\geq f_{ck} + 0.825 \times$ established standard deviation (rounded off to nearest $0.5 \, N/mm^{2}$ )or $f_{ck} + 3$ ,whichever is greater	$\geq f_{ck} - 3$
NOTES
1 In the absence of established value of standard deviation, the values given in Table 8 may be assumed, and attempt should be made to obtain results of 30 samples as early as possible to establish the value of standard deviation.2 For concrete of quantity up to $30 \, m^{3}$ (where the number of samples to be taken is less than four as per the frequency of sampling given in 14.2.2), the mean of test results of all such samples shall be $f_{ck} + 4 \, N/mm^{2}$ , minimum and the requirement of minimum individual test results shall be $f_{ck} - 2 \, N/mm^{2}$ , minimum. However, when the number of sample is only one as per 14.2.2, the requirement shall be $f_{ck} + 4 \, N/mm^{2}$ , minimum.

the hardened concrete may be accepted after carrying out suitable remedial measures to the satisfaction of the Engineer-in-Charge.