MCQs on Physical Quality of Concrete
Questions 12–22 — Tap an option to check your answer.
Q12: Ultimate creep coefficient of concrete:
Difficulty: Hard
Correct Answer: B. Decreases with age at loadingSolution:The ultimate creep coefficient (ratio of final creep strain to elastic strain) decreases as the age at loading increases. Concrete loaded at an early age has less hydration, is weaker, and experiences more creep. As concrete matures, more hydration products form, the paste becomes stiffer and denser, and creep decreases.
Q13: Shrinkage of concrete:
Difficulty: Hard
Correct Answer: A. Increases bond strengthSolution:Drying shrinkage causes the concrete to contract around the steel reinforcement bars. This contraction grips the steel more tightly, creating a mechanical interlock and friction that actually increases the bond strength between concrete and steel. This is why ribbed/deformed bars perform even better — shrinkage forces concrete into the deformations.
Q14: The ratio of 7-day strength to 28-day strength of ordinary Portland cement concrete is approximately:
Difficulty: Medium
Correct Answer: A. 0.65Solution:For ordinary Portland cement (OPC), the 7-day compressive strength is approximately 65% of the 28-day strength, giving a ratio of 0.65. This reflects the hydration kinetics of OPC: C₃S (the primary strength-giving compound) hydrates rapidly in the first 7 days, contributing about 65% of the 28-day strength, after which C₂S takes over for slower long-term strength gain.
Q15: To get 28-day strength from 7-day strength of OPC concrete, multiply by:
Difficulty: Easy
Correct Answer: C. 1.5Solution:Since f₇/f₂₈ ≈ 0.65, we have f₂₈ = f₇ / 0.65 = f₇ × 1.538 ≈ f₇ × 1.5. This approximation (multiply 7-day strength by 1.5) is the standard site practice to get a quick estimate of the expected 28-day strength. If the estimate is satisfactory, continue with the pour; if not, investigate the mix.
Q16: Match List I (concrete property) with List II (definition): P-Mobility, Q-Bleeding, R-Segregation, S-Consistency
Difficulty: Hard
Correct Answer: B. P-3, Q-4, R-2, S-1Solution:List II: 1-Firmness of concrete, 2-Separation of coarse aggregates, 3-Ability to be moulded, 4-Gain of water on surface. Match: P(Mobility)=3(ability to be moulded); Q(Bleeding)=4(gain of water on surface); R(Segregation)=2(separation of coarse aggregates); S(Consistency)=1(firmness of concrete).
Q17: Drying shrinkage in concrete is affected by:
Difficulty: Medium
Correct Answer: D. All options are correctSolution:Drying shrinkage is affected by all three: (A) Low relative humidity accelerates evaporation and increases shrinkage; (B) Shrinkage increases with time as concrete dries, reaching its ultimate value over months; (C) Higher w/c ratio means more evaporable free water, hence more shrinkage. IS 456 assumes a total drying shrinkage strain of 0.0003 in the absence of specific data.
Q18: Drying shrinkage of concrete can be reduced by:
Difficulty: Medium
Correct Answer: D. All options are correctSolution:All three methods reduce drying shrinkage: (A) Low w/c reduces free water, hence less water to evaporate; (B) Less cement means less paste volume (paste shrinks; aggregate does not); (C) Proper mix design with correct aggregate gradation and proportions minimises excess paste and voids. Using harder, stiffer aggregates also restrains paste shrinkage.
Q19: Too wet a concrete may cause:
Difficulty: Medium
Correct Answer: D. All of theseSolution:Too wet a mix causes all three defects: (A) Segregation — lower viscosity paste cannot hold heavy aggregates in suspension; (B) Lower density — excess water creates large capillary voids when it evaporates; (C) Lower strength — water-cement ratio is the primary factor governing concrete strength (Abrams’ Law). All three consequences reinforce each other.
Q20: Maximum shrinkage in concrete occurs after drying of:
Difficulty: Medium
Correct Answer: A. 28 daysSolution:The maximum rate of drying shrinkage occurs during the first 28 days after initial drying begins. This is when most of the free capillary water evaporates. Shrinkage continues beyond 28 days but at a much reduced rate, eventually approaching an asymptotic long-term value over months and years.
Q21: The density of concrete:
Difficulty: Medium
Correct Answer: C. Increases with increase in size of aggregatesSolution:Larger aggregate particles have relatively less surface area per unit volume, which means less cement paste is needed to coat them. This results in a denser concrete with more aggregate mass per unit volume. Also, large aggregates have a higher particle density (less internal voids) than the cement paste they replace, so the overall concrete density increases with larger aggregate.
Q22: Properties of concrete can be divided into:
Difficulty: Easy
Correct Answer: C. 2 (two)Solution:The properties of concrete are divided into two broad categories: (1) Properties of FRESH concrete — workability, consistency, bleeding, segregation; and (2) Properties of HARDENED concrete — compressive strength, durability, impermeability, creep, shrinkage, and modulus of elasticity.