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The target mean strength f_cm for concrete mix design obtained from the characteristic strength f_ck and standard deviation σ, as defined in IS:456-2000, is

1. f_ck + 1.35σ
2. f_ck + 1.45σ
3. f_ck + 1.5σ
4. f_ck + 1.65σ

Correct answer: f_ck + 1.65σ

Solution

The correct option, f_ck + 1.65σ, is derived from the need to ensure that the target mean strength accounts for variability in concrete strength, providing a higher safety margin to achieve the desired performance in structural applications.

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