Q31: In a slump test, each layer of concrete is compacted by a steel rod 60 cm long and of 16 mm diameter for:
Difficulty: Easy
A. 20 times
B. 25 times
C. 30 times
D. 40 times
Correct Answer: B. 25 timesSolution:As per IS 1199, each of the three layers of concrete in the slump cone is rodded (tamped) 25 times with the standard tamping rod (16 mm diameter, 600 mm long, bullet-nosed end). This ensures uniform compaction of each layer.
Q32: What is the range of slump (mm) of the concrete which is used as the mass concrete?
Difficulty: Easy
A. 10 to 15
B. 20 to 50
C. 50 to 75
D. 75 to 110
Correct Answer: B. 20 to 50Solution:Mass concrete (large unreinforced or lightly reinforced pours such as dam bodies, foundations, retaining walls) uses a low slump of 20-50 mm. Low workability is possible because the large cross-section is easy to vibrate and lower w/c reduces heat of hydration.
Q33: The main object of compaction of concrete is:
Difficulty: Easy
A. to eliminate air holes
B. to achieve maximum density
C. to provide intimate contact between the concrete and embedded materials
D. All options are correct
Correct Answer: D. All options are correctSolution:All three objectives are equally valid. Compaction serves to: (a) eliminate entrapped air voids; (b) achieve maximum density by expelling air and water pockets; (c) ensure the concrete fills all spaces around reinforcement bars, formwork corners, and embedded items.
Q34: Which of the following statements is false?
Difficulty: Medium
A. Workability of the concrete mix decreases with an increase in the moisture content
B. Concrete for which preliminary tests are conducted, is called controlled concrete
C. Bulking of sand depends upon the fineness of grains
D. All options are correct
Correct Answer: A. Workability decreases with increase in moisture contentSolution:Statement (a) is FALSE. Workability INCREASES with an increase in moisture (water) content, not decreases. More water in the mix increases fluidity and lubrication, reducing inter-particle friction. Statements (b) and (c) are correct.
Q35: How many hoppers are in compaction factor test of concrete?
Difficulty: Easy
Correct Answer: C. 2Solution:The Compacting Factor Apparatus (IS 5515) has 2 hoppers (one upper and one lower) stacked above a cylinder. The concrete falls from the upper hopper through the lower hopper into the cylinder, achieving partial compaction by gravity.
Q36: The slump test is performed to check the –
Difficulty: Easy
A. Presence of water in cement
B. Ratio of concrete ingredients
C. Temperature resistance
D. Workability of concrete
Correct Answer: D. Workability of concreteSolution:The slump test (IS 1199) is a field test performed on fresh concrete specifically to assess its workability (consistency). It measures the degree of fluidity of the mix.
Q37: Pick up the correct statement from the following.
Difficulty: Easy
A. Higher workability indicates unexpected increase in the moisture content
B. Higher workability indicates deficiency of sand
C. If the concrete mix is dry, the slump is zero
D. All options are correct
Correct Answer: D. All options are correctSolution:All three statements are correct. Unexpectedly high workability on site may indicate excess water or moisture (A). It may also indicate insufficient sand (B) as a rich cement-paste mix will flow more easily. A completely dry (earth-moist) mix will show zero slump (C).
Q38: The entrained air in concrete ………………
Difficulty: Easy
A. Increases workability
B. Decreases workability
C. Increases strength
D. None of these
Correct Answer: A. Increases workabilitySolution:Entrained air (intentionally introduced tiny air bubbles via air-entraining agents) increases workability because the microscopic spherical air bubbles act as a ball-bearing lubricant between aggregate particles, reducing internal friction.
Q39: The workability of concrete can be improved by:
Difficulty: Medium
A. More sand
B. More cement
C. More fine aggregate
D. Fineness of coarse aggregate
Correct Answer: B. More cementSolution:Increasing cement content (while maintaining the same w/c ratio) increases the total paste volume, which provides better lubrication of aggregate particles and improves workability. More fine aggregate or sand increases surface area and reduces workability. Finer coarse aggregate also increases surface area.
Q40: The top diameter, bottom diameter and the height of a slump mould are ……….
Difficulty: Easy
A. 10 cm, 20 cm, 30 cm
B. 10 cm, 30 cm, 20 cm
C. 20 cm, 10 cm, 30 cm
D. 20 cm, 30 cm, 10 cm
Correct Answer: A. 10 cm, 20 cm, 30 cmSolution:The slump cone dimensions per IS 1199 are: Top diameter = 10 cm (100 mm), Bottom diameter = 20 cm (200 mm), Height = 30 cm (300 mm). The top is the smaller opening and the bottom is the larger base.
Q41: Pick up the incorrect statement from the following.
Difficulty: Hard
A. A rich mix of concrete possesses higher strength than that a lean mix of desired workability with excessive quantity of water
B. The strength of concrete decreases as the water cement ratio increases
C. If the water cement ratio is less than 0.45, the concrete is not workable and causes honey combed structure
D. Good compaction by mechanical vibration, increases the strength of concrete
Correct Answer: A. A rich mix possesses higher strength than a lean mix with excessive waterSolution:Statement (a) is incorrect because strength depends solely on the water-cement ratio (Abrams’ Law), not on whether the mix is rich or lean. A lean mix with a properly controlled (low) w/c ratio can have equal or higher strength than a rich mix. Richness alone does not guarantee superior strength.
Q42: Pick up the correct statement from the following.
Difficulty: Medium
A. Segregation is necessary for a workable concrete
B. Consistency does not affect the workability of concrete
C. If the slump increases, workability decreases
D. None of these
Correct Answer: D. None of theseSolution:All three statements (a), (b), (c) are false. Segregation is HARMFUL (not necessary) for workable concrete. Consistency directly affects workability. Higher slump means higher workability (not lower). Therefore the correct choice is ‘None of these’.
Q43: For given water content, workability decreases if the concrete aggregates contain an excess of
Difficulty: Medium
A. Thin particles
B. Flat particles
C. Elongated particles
D. All options are correct
Correct Answer: D. All options are correctSolution:Thin, flat, and elongated particles all decrease workability because they have a high surface-area-to-volume ratio (more water needed to coat them) and they interlock and bridge, creating more mechanical resistance to flow.
Q44: The test most suitable for concrete of very low workability is ……………..
Difficulty: Medium
A. Slump test
B. Compaction factor test
C. Vee-Bee test
D. All options are correct
Correct Answer: C. Vee-Bee testSolution:The Vee-Bee consistometer test is most suitable for very low workability concrete (VB time > 10 seconds). At very low workability, the slump is zero (slump test fails) and the compaction factor difference is too small for reliable discrimination.
Q45: A concrete having a slump of 6.5 cm is said to be ………..
Difficulty: Easy
A. dry
B. earth moist
C. semi-plastic
D. plastic
Correct Answer: D. plasticSolution:A slump of 6.5 cm = 65 mm falls in the 50-100 mm range, which corresponds to medium workability — described as ‘plastic’ consistency in IS terminology. Plastic concrete flows and compacts readily.
