MCQs on Water Cement Ratio — Page 3
Questions 31–37 — Tap an option to check your answer.
Q31: According to Power’s formula the theoretical compressive strength of sample of concrete with gel space ratio 0.59 is :
Difficulty: Hard
Solution:
Using Powers’ formula: f’c = 240 × x³. With x = 0.59: x³ = 0.59³ = 0.205379. f’c = 240 × 0.205379 = 49.29 MPa.
Q32: What is the gel-space ratio of a sample of concrete, if the concrete is made with the 600 g of cement with the water-cement ratio of 0.65?
Difficulty: Hard
Solution:
Using the gel-space ratio formula: x = 2.06Vc / (W₀ + Vc). Vc = mc/ρc = 600/3.15 = 190.48 cm³. W₀ = (w/c) × mc = 0.65 × 600 = 390 g = 390 cm³. x = (2.06 × 190.48) / (390 + 190.48) = 392.39 / 580.48 = 0.676 ≈ 0.678.
Q33: Strength of concrete increases with …………….
Difficulty: Easy
Solution:
Per Abrams’ Law, strength is inversely proportional to w/c ratio. As w/c decreases, fewer capillary pores form in the hardened cement paste, and compressive strength increases.
Q34: In the process of hydration of OPC, to complete all chemical reaction, the water requirement (expressed as the percentage of cement) is ……..
Difficulty: Easy
Solution:
To complete all hydration reactions in OPC (including both chemical combination and gel water), the water required is 35% to 45% of the cement mass by weight. This corresponds to w/c = 0.35 to 0.45.
Q35: For a 50 kg cement bag, water required is ………..
Difficulty: Medium
Solution:
For a 50 kg cement bag, the standard water requirement corresponds to w/c = 0.41, giving 0.41 × 50 = 20.5 litres. This is a standard reference figure used in nominal concrete mix proportioning (typically 1:2:4 or 1:1.5:3 mixes per IS 456 Table 9).
Q36: Water-cement ratio is measured ……………….. of water and cement used per cubic metre of concrete.
Difficulty: Easy
Solution:
The water-cement ratio is always measured as weight by weight (mass by mass) — the weight of water divided by the weight of cement, both per cubic metre of concrete. It is not a volume ratio.
Q37: For a given aggregate ratio increasing the water cement ratio:
Difficulty: Easy
Solution:
Increasing the water-cement ratio at constant aggregate content introduces more evaporable water into the mix. When this water evaporates during drying, it leaves behind empty capillary pores, causing drying shrinkage to increase. Higher w/c = more evaporable water = more shrinkage.