Q46: Slump test is a measure of ………….
Difficulty: Easy
A. Tensile strength
B. Compressive strength
C. Impact value
D. Consistency
Correct Answer: D. ConsistencySolution:The slump test measures the consistency (and by extension, the workability) of fresh concrete. A higher slump indicates greater consistency and higher workability; a lower slump indicates a stiffer, drier mix.
Q47: If the compaction factor is 0.95, the workability of concrete is:
Difficulty: Easy
A. Very low
B. Low
C. Medium
D. High
Correct Answer: D. HighSolution:A compaction factor of 0.95 corresponds to high workability. The IS 7320 classification: CF < 0.75 = very low, 0.75-0.85 = low, 0.85-0.92 = medium, > 0.92 = high. CF 0.95 > 0.92, therefore high workability.
Q48: Which of the following method may be used for getting a more workable concrete?
Difficulty: Easy
A. By increasing cement content
B. By decreasing water cement ratio
C. By using angular aggregates in place of rounded ones
D. By reducing the size of aggregates
Correct Answer: A. By increasing cement contentSolution:Increasing cement content (at the same w/c ratio) increases the paste volume, which acts as lubricant and improves workability. Decreasing w/c (B) reduces workability. Angular aggregates (C) create more friction, reducing workability. Reducing aggregate size (D) increases surface area and reduces workability.
Q49: Workability of concrete is directly proportional to which of the following? (i) Time of transit (ii) Water cement ratio (iii) Grading of aggregate (iv) Strength of concrete (v) Aggregate cement ratio
Difficulty: Hard
A. (ii), (iii), (v)
B. (ii), (iii)
C. (iii), (iv), (v)
D. (i), (ii), (iv)
Correct Answer: B. (ii) and (iii)Solution:Workability is directly proportional to water-cement ratio (ii) – more water means more fluidity, and grading of aggregate (iii) – well-graded aggregate packs efficiently with less void and less surface area per m³. Time of transit (i) reduces workability (cement hydrates over time). Strength (iv) is inversely related to workability (high w/c = high workability but low strength). A/C ratio (v) generally reduces workability (more aggregate = more surface area).
Q50: In a mix if the desired slump is not obtained, the adjustment for each concrete slump difference is made by adjusting water content by:
Difficulty: Medium
A. 0.25%
B. 0.5%
C. 0.75%
D. 1%
Correct Answer: B. 0.5%Solution:Per IS 10262, for each 25 mm change in desired slump, the water content is adjusted by ±0.5%. If slump is 25 mm higher than target, reduce water by 0.5%. If slump is 25 mm lower, add 0.5% more water.
Q51: Workability of concrete is directly proportional to
Difficulty: Medium
A. Aggregate-to-cement ratio
B. Time of transit
C. Grading of aggregate
D. Water-to-cement ratio
Correct Answer: C. Grading of aggregateSolution:Among the options given, grading of aggregate is directly proportional to workability. Well-graded aggregates create a more efficient packing, reducing voids and requiring less water for the same workability. Note: though w/c is also directly proportional, the specific answer key for this question selects grading of aggregate (C), possibly because option D lists ‘Water to cement ratio’ but the answer selection is C.
Q52: Low workability of concrete conforms to a slump of:
Difficulty: Easy
A. 25-75 mm
B. 50-100 mm
C. 75-100 mm
D. 100-150 mm
Correct Answer: A. 25-75 mmSolution:Per IS 456 and standard classification, low workability corresponds to a slump of 25-75 mm. This range is suitable for lightly reinforced sections, pavements, and applications accessible by vibration. Slumps of 50-100 mm indicate medium workability; 100-150 mm indicates high workability.
Q53: Presence of oil in water for concrete:
Difficulty: Easy
A. Gives smooth surface
B. Gives more slumps
C. Improves strength
D. Reduces strength
Correct Answer: D. Reduces strengthSolution:Oil contamination in mixing water interferes with the cement hydration process. Oil coats cement particles, preventing proper bonding and reducing strength. Even small amounts of oil (petroleum, lubricating oils) can significantly reduce compressive strength of concrete.
Q54: The value of Vee-Bee time for low workability as per Indian standards is prescribed as
Difficulty: Medium
A. 2-5 seconds
B. 5-10 seconds
C. 20 seconds
D. 20-30 seconds
Correct Answer: B. 5-10 secondsSolution:Per IS 1199 / IS 7320, the Vee-Bee time for LOW workability is 5-10 seconds. Very low workability = above 10 seconds; medium = 3-5 seconds; high workability = 0-3 seconds.
Q55: For a constant water cement ratio, decrease in aggregate cement ratio causes
Difficulty: Medium
A. Increase in workability
B. Decrease in workability
C. No change in workability
D. None of these
Correct Answer: A. Increase in workabilitySolution:Decreasing the aggregate-cement (A/C) ratio at constant w/c means increasing the cement paste content relative to aggregate. More paste = better lubrication of aggregate particles = higher workability. The mix becomes richer in paste, flowing more easily.
Q56: The workability of concrete is influenced most by its
Difficulty: Easy
A. Water-cement ratio
B. Aggregate cement ratio
C. Cement ratio
D. Water content
Correct Answer: A. Water-cement ratioSolution:The water-cement (w/c) ratio is the single most influential factor on both workability and strength of concrete. A higher w/c ratio increases the free water available to lubricate aggregates, directly increasing workability.
Q57: As per IS 13311 (Part 1), in the ultrasonic test for hardened concrete, good quality of concrete is indicated if the pulse velocity is:
Difficulty: Hard
A. More than 4.5 km/s
B. Between 3.0 km/s to 3.5 km/s
C. Between 3.5 km/s to 4.5 km/s
D. Less than 3.0 km/s
Correct Answer: C. Between 3.5 km/s to 4.5 km/sSolution:Per IS 13311 Part 1 (Ultrasonic Pulse Velocity), good quality concrete has a pulse velocity of 3.5-4.5 km/s. Excellent quality is >4.5 km/s. Medium quality is 3.0-3.5 km/s. Doubtful quality is <3.0 km/s.
Q58: What is the effect on the strength of concrete on addition of pozzolanas, keeping other factors same?
Difficulty: Hard
A. The ultimate strength decreases
B. The early strength and ultimate strength both increase
C. The early strength decreases but ultimate strength remains almost same
D. There is no change in the ultimate strength
Correct Answer: C. Early strength decreases but ultimate strength remains almost sameSolution:Pozzolanas (fly ash, GGBS, silica fume) react with Ca(OH)2 released during cement hydration in a secondary ‘pozzolanic reaction’. This reaction is slow, so: early-age strength is lower (less initial C-S-H formation), but ultimate (long-term) strength is approximately equal or slightly higher than plain cement concrete.
Q59: The percentage of fly ash used in high volume fly ash concrete is:
Difficulty: Medium
A. 10-25%
B. 70-80%
C. Greater than 90%
D. 50-60%
Correct Answer: D. 50-60%Solution:High Volume Fly Ash (HVFA) concrete, developed by CANMET (Canada) and studied by Malhotra and Mehta, uses 50-60% fly ash by mass of total cementitious material. This significantly reduces OPC clinker content, heat of hydration, and CO2 emissions while maintaining adequate long-term strength.
Q60: Workability of concrete for a given water content is good if the aggregates are:
Difficulty: Easy
A. Rounded aggregate
B. Irregular aggregate
C. Angular aggregate
D. Flaky aggregate
Correct Answer: A. Rounded aggregateSolution:Rounded aggregates (river gravels, natural rounded sand) give the best workability for a given water content because their smooth, spherical shape reduces inter-particle friction. Angular and irregular aggregates have rough surfaces and interlock with each other, requiring more water to achieve the same workability.
