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GATE 2023 CE (CE2) – Question 15

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

M20 concrete as per IS 456: 2000 refers to concrete with a design mix having _________________.

  1. an average cube strength of 20 MPa
  2. an average cylinder strength of 20 MPa
  3. a 5-percentile cube strength of 20 MPa
  4. a 5-percentile cylinder strength of 20 MPa

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Correct answer: (C) a 5-percentile cube strength of 20 MPa

Explanation

In IS 456:2000 the grade letter M stands for mix, and the number is the **characteristic compressive strength** of a **150 mm cube** at 28 days in MPa.

**Characteristic strength** is defined statistically: the value below which not more than **5%** of the test results are expected to fall (the 5-percentile value).

So M20 means a 5-percentile **cube** strength of 20 MPa. It is not an average strength and it is not a cylinder strength.

Answer **C**.