Guidelines to follow for acceptance criteria for concrete
As per IS 456 : 2000 (C1 15.1), it is known that 28 days compressive strength shall individually be the standard for approval and disapproval of concrete.
But as per IS 456 : 2000 (C1 16), there exist two criterion for acceptance of concrete that range from compressive strength and flexural strength.
Prior to arrange test results for acceptance criteria, it is necessary to examine validation i.e. whether the sample is proper or improper for acceptance criteria.
The test results should be as follow :-
Test results are average of three specimens.
Individual deviation should be under ± 15% of the average.
Suppose M25 grade of concrete is applied in the construction. Let strength of specimen for first one should be 28.5 MPa (Mega Pascal). For the second one, it should be at 26 mega pascal and for third one, it should be 29 mega pascal.
By summing up, we get the average as 27.83 MPa (mega pascal).
If the individual deviation is computed from the average for first specimen, it shall be 2.4%.
For second, it shall be -6.57%
For third, it shall be 4.20%
From the test result, it can be said that the specimens are legitimate for acceptance criteria as the deviation of individual sample does not surpass 15%.
To get more details, go through the following video tutorial.