Q1: Which of the following methods is NOT used for measuring air content in fresh concrete?
Difficulty: Medium
A. Blaine air permeability method
B. Gravimetric method
C. Pressure method
D. Volumetric method
Correct Answer: A. Blaine air permeability methodSolution:The Blaine air permeability apparatus measures the fineness (specific surface area) of dry cement — not air content. The three standard methods for measuring air content in fresh concrete are: Gravimetric method, Pressure method, and Volumetric method (all per IS 1199).
Q2: Separation of coarse aggregates from mortar during transportation is known as:
Difficulty: Easy
A. Bleeding
B. Creeping
C. Segregation
D. Shrinkage
Correct Answer: C. SegregationSolution:Segregation is the separation of the constituent materials of concrete — specifically the coarse aggregate from the cement-sand mortar. It commonly occurs during transportation when concrete is jolted or dropped, causing heavy aggregates to settle and separate. IS 456 limits the drop height to 1.5 m to prevent segregation.
Q3: Bleeding is good to an extent if it occurs when concrete is:
Difficulty: Medium
A. Transported
B. Mixed
C. Plastic
D. Placed
Correct Answer: C. PlasticSolution:Minor bleeding while concrete is still in the plastic state (freshly placed and workable) is tolerable. It helps lubricate the surface for finishing operations. However, excessive bleeding at any stage reduces impermeability, weakens the top surface layer (laitance), and creates capillary channels that make the concrete porous.
Q4: Excess vibration during compacting of concrete can lead to:
Difficulty: Medium
A. Bleeding
B. Segregation
C. High strength
D. Air bubbles
Correct Answer: B. Segregation (Note: Commission revised answer key considered this question incorrect)Solution:Note: The commission’s revised answer key considered this question incorrect/invalidated. In standard texts, the primary result of over-vibration is segregation — heavy aggregates sink while cement paste and water rise. Bleeding is a closely related secondary effect. The standard accepted answer for this question is (b) Segregation.
Q5: The risk of segregation is more for:
Difficulty: Medium
A. Wetter mix
B. Larger proportion of maximum size aggregate
C. Coarser grinding of cement
D. All options are correct
Correct Answer: D. All options are correctSolution:All three factors increase segregation risk: (A) Wetter mixes have lower cohesion; (B) Larger maximum aggregate size means heavier particles that settle faster; (C) Coarser cement grinding produces a less cohesive paste that cannot suspend aggregates as effectively. Additionally, segregation increases voids — 2% voids reduces strength by 10%, 5% voids by over 30%.
Q6: Which of the following statements is true? A. Impermeability is a property of fresh concrete. B. Impermeability is NOT a property of fresh concrete. C. Impermeability has nothing to do with concrete at all.
Difficulty: Medium
A. Only A (Impermeability is a property of fresh concrete)
B. Only B (Impermeability is NOT a property of fresh concrete)
C. Both A and B
D. None of these
Correct Answer: B. Only B (Impermeability is NOT a property of fresh concrete)Solution:Impermeability is a property of hardened concrete, not fresh concrete. Fresh concrete is plastic and fluid — impermeability is irrelevant at this stage. Once concrete hardens, its resistance to water permeation (impermeability) becomes a critical durability property.
Q7: The accumulation of water on outer surface of concrete is:
Difficulty: Easy
A. Transpiration
B. Bleeding
C. Guttation
D. Ponding
Correct Answer: B. BleedingSolution:Bleeding is the phenomenon where free mix water rises to the surface of freshly placed concrete due to the settlement of heavier solid particles (cement, aggregate). The water on the surface also carries fine particles of cement and sand. Bleeding makes concrete porous by creating upward capillary channels.
Q8: To prevent segregation, the maximum height of placing concrete is:
Difficulty: Easy
A. 100 cm
B. 125 cm
C. 150 cm
D. 200 cm
Correct Answer: C. 150 cmSolution:IS 456:2000 specifies that to prevent segregation, concrete should not be dropped/placed from a height greater than 150 cm (1.5 m). When dropped from greater heights, the kinetic energy of impact causes coarse aggregates to bounce and roll away from the cement-sand mortar.
Q9: Which is the most important factor that affects the shrinkage of cement concrete?
Difficulty: Medium
A. Quantity of cement
B. Size of coarse aggregates
C. Size of fine aggregate
D. Amount of water added during mixing
Correct Answer: D. Amount of water added during mixingSolution:The amount of mixing water is the most important factor affecting concrete shrinkage. Water that is not consumed by cement hydration must eventually evaporate, and this loss of volume causes drying shrinkage. A higher water-cement ratio means more free water, more evaporation, and more shrinkage. Aggregate (fine and coarse) actually restrains shrinkage.
Q10: Durability of concrete is proportional to:
Difficulty: Medium
A. Sand content
B. Water-cement ratio
C. Aggregate ratio
D. Cement-aggregate ratio
Correct Answer: D. Cement-aggregate ratioSolution:Durability of concrete is directly proportional to the cement-aggregate ratio. More cement relative to aggregate means a richer mix with better binder content, denser paste, and lower permeability — all of which extend the service life. However, durability is also heavily influenced by permeability, which is inversely related to w/c ratio.
Q11: The durability of concrete is affected by:
Difficulty: Medium
A. Cider
B. Vinegar
C. Alcohol
D. Both cider and vinegar
Correct Answer: D. Both cider and vinegarSolution:Cider (apple-based acidic drink) and vinegar (acetic acid solution) are both acidic substances that react with calcium hydroxide (Ca(OH)₂) in hardened concrete, degrading the cement matrix and reducing durability. Alcohol (option C) does not significantly attack concrete under normal conditions.
