Correct Answer - Option 4 : 15%
Concept:
As per IS 456: 2000, CL 17.4, Concrete in the member represented by a core test shall be considered acceptable if the average equivalent cube strength of the cores is equal to at least 85 percent of the cube strength of the grade of concrete specified for the corresponding age i.e. maximum reduction allowed is 15 %. Also, no individual core has a compressive strength less than 75 percent.
Additional Information:
1. The core test on concrete is generally done, when result of concrete cube strength fails.
2. The minimum three nos. of cores shall be considered for testing.
3. As per IS 456:2000, codal provisions, the maximum individual variation allowed in compressive strength of concrete cube is ± 15 % of the test result. Here, test result will be the average compressive strength of the 3 cube specimens.
