Question

If the characteristic strength of concrete $f_{ck}$ is defined as the strength below which not more than 50% of the test results are expected to fail, the expression for $f_{ck}$ in terms of mean strength $f_m$ and standard deviation $\overline{\sigma }$ would be

• A. $f_m-0.1645\overline{\sigma }$
• B. $f_m-1.645\overline{\sigma }$
• C. $f_m$
• D. $f_m+1.645\overline{\sigma }$

Answer 1

The correct option is C $f_m$

$f_{ck}$ is defined as the strength below which 50% of test results are expected to fail from curve.

For curve


$f_{ck}=f_m$