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GATE 2017 CE (CE2) – Question 25

Construction Materials · Concrete: constituents, mix design, short-term and long-term properties · 1 mark · Multiple choice

Characteristic strength is defined here as the strength below which not more than 50% of test results are expected to fall. With standard deviation 4 MPa, the target mean strength of M25 concrete is ______ MPa.

  1. 18.42
  2. 21.00
  3. 25.00
  4. 31.58

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Show answer and explanation

Correct answer: (C) 25.00

Explanation

The source explicitly states a 50% threshold. For a symmetric normal distribution, the 50th percentile is the mean, so the target mean is 25 MPa (C). The usual 5% criterion would instead yield $25+1.645(4)=31.58$ MPa, but that answers a different threshold.