I have concrete cube test results with 24.3 MPa average which should has been 25 MPa But the Standard deviation of the results is 3.39. Is this acceptable with reference to BS Code.
As far as I know, the deviation specified in the standard is for the resistance of each sample, and the mean resistance of all samples should not be less than 25 MPa. For example, you can have one sample with a resistance of 21.61 MPa provided that the average resistance of all samples is not less than 25 MPa.
Malshan Nallaperuma ... Both according to ACI and BS... that was not acceptable ... need to add 10% to the required... i.e. need at least 28MPa
Regards..
A minimum of 30 test results are required.For general construction testing standard deviation below 2.8 is excellent. 2.8-3.4 is coming under very good category.
The standard deviation depends on the quality control has to be exercised at site. For fair and very good quality control the values shall be changing.
Moreover you will need 30 samples as early as possible to find out the standard deviation in the particular activity.
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