The GATE Grind

GATE 2024 CE (CE1) – Question 15

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

Concrete of characteristic strength 30 MPa is required. If 40 specimens of concrete cubes are to be tested, the minimum number of specimens having at least 30 MPa strength should be

  1. 35
  2. 37
  3. 38
  4. 39

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Correct answer: (C) 38

Explanation

The characteristic strength is the value below which not more than 5% of the test results are expected to fall. So at least 95% of the 40 specimens must reach 30 MPa: $0.95 \times 40 = 38$.