Answer:- Standard deviation is evaluated to know the quality of measurements or results.
According to IS 456-2000 Assumed standard deviation of M25 is 4 N/mm2
The value of comprehensive strength to be achieved at 28 days for M25 grade of concrete is 25 N/mm2
Above is perfect answer but we must remember when we check street of cubes SD must be added to its grade that is if M 25 concrete cubes is being tested it’s strength should be around 29 N/mm2 and if you are testing actual elements strength through UPV , rebound hammer or Core samples them it should be equal to 25 N / mm2
Again there is criteria of 15 % variation in sample of 3cubes average strength. Variation in individual cube should not be more or less than 15 % with average of three samples.
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