Compressive strength test results

[tttooktook]

If the 28 days compressive strength test result of 3nos cylinders of same set varies , for how much deviation the avg result cannot be formed??

 

[Ron]

Depends on your code. Generally the strength is the average of two tests at 28 days. If they vary from the design strength by more than 10 percent low, I would investigate.

 

[BigH]

In India it is 15% variation on the average - they do three tests per each date.

 

[DETstru]

I'm not sure where you're located but here in the US we abide by ASTM C39 Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens.

FYI- It's a great document to own and I reference it frequently.

It indicates that the average of 3 consecutive tests must equal or exceed the specified f'c. Also, no single test should fall below the specified f'c by more than 500 psi (3.45 MPa), or, for 5,000 psi (35 MPa) concrete or stronger, no more than 10% of f'c.