For a concrete mix with a characteristic strength of M40, if the standard deviation of compressive strength is 5 MPa, then what should be the target mean strength of the mix?
- A40 MPa
- B45 MPa
- C48.25 MPaCorrect
- D52 MPa
Solution
Concept
Target strength
Formula
ft = fck + 1.65 s
Step-by-step solution
1. 40 + 1.65 × 5 = 48.25 MPa.
Explanation
The mix must be designed for a higher mean strength than the characteristic strength.
Why the other options are wrong
40 and 45 are too low; 52 is too high.
Shortcut
fck + 1.65 s.
Correct answer: C) 48.25 MPa