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GATE 2025 CE (CE2) – Question 23

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

In the context of construction materials, which of the following statements is/are CORRECT?

  1. If the characteristic strength is defined as that value below which not more than 50% results are expected to fall, the target mean strength in mix design will be taken same as the characteristic strength irrespective of the degree of quality control expected at the site.
  2. Ten percent fines value is a non-dimensional quantity.
  3. The stress-strain curve of concrete for 1-day duration of loading is associated with a smaller secant modulus of elasticity compared to the stress-strain curve of the same concrete for 10-minutes duration of loading.
  4. The increase of carbon in steel usually leads to an increase in its 0.2% proof stress.

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Show answer and explanation

Correct answer: (A) If the characteristic strength is defined as that value below which not more than 50% results are expected to fall, the target mean strength in mix design will be taken same as the characteristic strength irrespective of the degree of quality control expected at the site.; (C) The stress-strain curve of concrete for 1-day duration of loading is associated with a smaller secant modulus of elasticity compared to the stress-strain curve of the same concrete for 10-minutes duration of loading.; (D) The increase of carbon in steel usually leads to an increase in its 0.2% proof stress.

Explanation

A: the target mean strength is $f_{ck} + k s$ and for 50% of results below the characteristic value, $k = 0$, so the target mean equals $f_{ck}$ whatever the standard deviation. B is false because the ten percent fines value is a load (in kN). C: creep under a long duration of loading increases the strain at the same stress, so the secant modulus is smaller. D: more carbon makes steel stronger and increases its proof stress.