MCQs on Physical Quality of Concrete
Questions 23–31 — Tap an option to check your answer.
Q23: Bleeding is defined as:
Difficulty: Easy
Correct Answer: A. Separation of water, sand, and cement from fresh concrete mixSolution:Bleeding is the upward migration of water (accompanied by fine particles of sand and cement) from freshly placed concrete. The heavier coarse aggregate and cement particles settle downward, displacing the lighter water and fines upward to the surface. This leaves a water-rich layer on the surface called laitance.
Q24: Segregation can be defined as the tendency of:
Difficulty: Easy
Correct Answer: B. Coarse aggregate to separate from the mortarSolution:Segregation is specifically defined as the tendency of coarse aggregate to separate from the cement-sand mortar in a concrete mix. This occurs when the cohesion of the mix is insufficient to keep the heavy aggregate in suspension, causing it to settle or roll away from the mortar phase.
Q25: Permanent dimensional changes of concrete under loading is known as:
Difficulty: Medium
Correct Answer: C. CreepSolution:Creep is the time-dependent, permanent (irreversible) deformation of concrete under sustained (constant) loading. Unlike elastic deformation (which is immediate and recoverable), creep continues to accumulate over time as long as the load is applied, and does not fully recover upon unloading. Shrinkage occurs even without loading (due to drying).
Q26: Concrete on drying after casting:
Difficulty: Easy
Correct Answer: C. ShrinksSolution:Concrete shrinks (reduces in volume) on drying after casting. This is drying shrinkage — as the free water and gel water evaporate from the capillary pores and gel pores of the hardened cement paste, surface tension forces and loss of water cause the paste to contract. IS 456 allows for a design shrinkage strain of 0.0003.
Q27: Increased cohesiveness of concrete makes it:
Difficulty: Medium
Correct Answer: A. Less liable to segregationSolution:Cohesiveness is the ability of concrete to remain as a single, stable mass without the constituents separating. Higher cohesiveness means the paste has a higher yield stress and viscosity, which better holds the aggregate particles in suspension and prevents them from settling or separating. Therefore, increased cohesiveness directly reduces segregation risk.
Q28: Efflorescence of concrete is manifested as:
Difficulty: Medium
Correct Answer: B. White fluffy layers on the concrete surfaceSolution:Efflorescence is the appearance of white fluffy, powdery, or crystalline deposits on the surface of concrete or masonry. It is caused by water dissolving soluble calcium salts (primarily Ca(OH)₂) from within the concrete and transporting them to the surface, where they react with CO₂ in the air to form insoluble calcium carbonate (CaCO₃) — a white precipitate.
Q29: The condition for no shrinkage is when relative humidity is:
Difficulty: Hard
Correct Answer: A. 1 (100%)Solution:Drying shrinkage is driven by the evaporation of water from the concrete’s pore system. If the relative humidity (RH) of the surrounding environment is 100% (RH = 1.0), there is no vapour pressure gradient between the concrete’s pore water and the environment — evaporation cannot occur. Therefore, with RH = 1.0 (fully saturated environment), drying shrinkage is zero.
Q30: The factors that influence the durability of concrete include:
Difficulty: Medium
Correct Answer: D. All options are correctSolution:Concrete durability is governed by all three factors: (A) Abrasion wears the surface mechanically; (B) Chemical action by acids, sulfates, chlorides, and other aggressive agents degrades the cement matrix; (C) Weathering — freeze-thaw cycles, thermal expansion/contraction, and carbonation — physically and chemically degrade the concrete over time. IS 456:2000 addresses all these aspects in exposure classification.
Q31: Shrinkage of concrete is directly proportional to:
Difficulty: Medium
Correct Answer: A. Cement contentSolution:Drying shrinkage is directly proportional to the cement content because shrinkage is primarily a property of the cement paste (not the aggregate). More cement means more paste, which shrinks on drying. Aggregate actually restrains shrinkage. While w/c ratio also influences shrinkage, the direct proportionality stated in the question refers to cement content as the key variable.