Q16: For batching 1:3:6 concrete mix by volume, which of the following are the ingredients required per bag of 50 kg cement?
Difficulty: Hard
A. 70 litres of sand and 120 litres of aggregates
B. 70 kg of sand and 140 litres of aggregates
C. 105 litres of sand and 140 litres of aggregates
D. None of these
Correct Answer: D. None of theseSolution:Per bag (35 L cement): Sand = 3 × 35 = 105 L. Coarse aggregate = 6 × 35 = 210 L. Option (c) has correct sand (105 L) but wrong CA (140 L instead of 210 L). No option matches both correct values, so the answer is ‘None of these.’
Q17: Batching error means inaccuracy in the quantity of:
Difficulty: Easy
A. Aggregates
B. Cement
C. Water
D. All options are correct
Correct Answer: D. All options are correctSolution:Batching error refers to any inaccuracy in measuring the quantities of concrete ingredients during batching. This includes all three — cement, aggregates, and water. Even a small error in any one ingredient alters the water-cement ratio, workability, and strength.
Q18: If X, Y and Z are fineness modulus of coarse, fine and combined aggregates respectively, the percentage (P) of fine aggregates to combined aggregates is:
Difficulty: Hard
A. P = ((Z – X) / (Z – Y)) × 100
B. P = ((X – Z) / (X – Y)) × 100
C. P = ((X – Z) / (Z + Y)) × 100
D. P = ((X + Z) / (Z – Y)) × 100
Correct Answer: B. P = ((X – Z) / (X – Y)) × 100Solution:The aggregate blending formula: P × FM_fine + (100-P) × FM_coarse = 100 × FM_combined. Rearranging with X = FM_coarse, Y = FM_fine, Z = FM_combined gives P = ((X – Z) / (X – Y)) × 100.
Q19: Pick up the correct statement from the following: A. The free water is the amount of water added while mixing and the amount of water held on the surface of the aggregates prior to mixing. B. The total water is the free water and the amount actually absorbed by the aggregates.
Difficulty: Medium
A. Only A
B. Only B
C. Neither A nor B
D. Both A and B
Correct Answer: D. Both A and BSolution:Both statements correctly define the water terminology used in concrete mix design. Free water (effective water) = mixing water added + surface (adsorbed) water on aggregate particles. Total water = free water + water absorbed into the aggregate pores (absorption water). IS 10262 uses these definitions in water content calculations.
Q20: If the effective working time is 7 hours and per batch time of concrete is 3 minutes, the output of a concrete mixer (in litres) of 150-litre capacity is:
Difficulty: Hard
A. 15900
B. 16900
C. 17900
D. 18900
Correct Answer: D. 18900Solution:Applying 90% efficiency for a concrete mixer: effective time = 7 h × 0.90 = 6.3 h = 378 min. Batches = 378 ÷ 3 = 126. Output = 126 × 150 = 18,900 litres.
Q21: Proper proportioning of concrete, ensures:
Difficulty: Easy
A. Desired strength and workability
B. Desired durability
C. Water tightness of the structure
D. All options are correct
Correct Answer: D. All options are correctSolution:Proper mix proportioning ensures all three simultaneously: (a) desired strength and workability by correctly balancing w/c ratio and aggregate content; (b) desired durability by limiting maximum w/c and ensuring adequate cover; (c) water tightness by achieving a dense, well-compacted matrix with minimum permeable porosity.
Q22: On which of the following does the correct proportion of ingredients of concrete depend upon?
Difficulty: Easy
A. Bulking of sand
B. Water content
C. Absorption and workability
D. All options are correct
Correct Answer: D. All options are correctSolution:The correct proportion of concrete ingredients depends on all three: (a) bulking of sand affects the actual volume of fine aggregate in a volume-batched mix; (b) water content is the most critical parameter controlling w/c ratio, strength and workability; (c) aggregate absorption and required workability both influence the free water demand of the mix.
Q23: The ratio of various ingredients (cement, sand, aggregates) in concrete of grade M 20 is:
Difficulty: Easy
A. 1:2:4
B. 1:3:6
C. 1:1.5:3
D. 1:1:2
Correct Answer: C. 1:1.5:3Solution:The nominal mix ratios per IS 456 are: M10 = 1:3:6, M15 = 1:2:4, M20 = 1:1.5:3, M25 = 1:1:2. M20 (28-day characteristic strength 20 N/mm²) corresponds to 1:1.5:3.
Q24: For which of the following grades ordinary concrete is not used?
Difficulty: Medium
A. M10
B. M40
C. M20
D. M25
Correct Answer: B. M40Solution:IS 456 classifies concrete as: Ordinary (M10, M15), Standard (M20–M55), and High Performance (M60–M80). M40 falls in the ‘Standard’ category, not ‘Ordinary.’ Ordinary concrete is only M10 and M15, which use nominal mixes without detailed design.
Q25: The 28 day’s cube strength of mass concrete using aggregates of maximum size 5cm for gravity dams should be:
Difficulty: Hard
A. Between 150 to 300 kg/sq.cm
B. Between 350 to 600 kg/sq.cm
C. Between 150 to 500 kg/sq.cm
D. Below 200 kg/sq.cm
Correct Answer: D. Below 200 kg/sq.cmSolution:Mass concrete for gravity dams uses large aggregates (up to 150 mm), low cement content, and low w/c to minimise heat of hydration. The design strength is intentionally low (below 200 kg/cm² = ~20 N/mm²) because gravity dams rely primarily on self-weight, not high material strength, for stability.
Q26: Pick up the INCORRECT statement from the following. While performing preliminary test on concrete:
Difficulty: Medium
A. Proportions of the material and water should be the same as to be used at the work site
B. Cement should be mixed by hand in order to maintain uniformity
C. Concrete mix should be stored in air-tight containers
D. Concrete ingredients should be kept at a temperature of 37° ± 2° C
Correct Answer: D. Ingredients at 37° ± 2° CSolution:Statement D is INCORRECT. Concrete ingredients should be maintained at 27°C ± 2°C (room temperature per IS 516), not 37°C. Testing at elevated 37°C temperature would artificially accelerate hydration, reduce workability, and give lower-than-actual compressive strength results, making the test results non-representative of site conditions.
Q27: If the various concrete ingredients i.e. cement, sand, aggregates are in the ratio of 1 : 3 : 6, the grade of concrete is:
Difficulty: Easy
A. M10
B. M15
C. M20
D. M30
Correct Answer: A. M10Solution:The nominal mix ratio 1:3:6 corresponds to M10 grade concrete (characteristic compressive strength = 10 N/mm² at 28 days). This is the leanest ordinary concrete mix per IS 456.
Q28: For the construction of the retaining structures, the type of concrete mix to be used is:
Difficulty: Medium
A. 1:3:6
B. 1:2:4
C. 1:1.5:3
D. 1:1:2
Correct Answer: C. 1:1.5:3Solution:Retaining structures (retaining walls, abutments) must withstand active earth pressure, often in contact with soil moisture and aggressive environments. M20 (1:1.5:3) is the minimum grade recommended per IS 456 for reinforced retaining structures, providing adequate strength and impermeability.
Q29: M15 concrete is used for:
Difficulty: Easy
A. Dams
B. Foundation
C. R.C.C.
D. Mass concreting works
Correct Answer: B. FoundationSolution:M15 (1:2:4 nominal mix, 15 N/mm² strength) is used for foundations (plain concrete footings, column pad foundations, retaining wall bases). It is too weak for structural RCC members (min M20) but suitable for foundations and plain concrete works.
Q30: In the symbol used to represent the concrete mix, MX. M stands for mix and numeric X represents the:
Difficulty: Easy
A. 7 days compressive strength
B. 14 days compressive strength
C. 28 days compressive strength
D. 28 days tensile strength
Correct Answer: C. 28 days compressive strengthSolution:In the designation MX, M = Mix and X = characteristic compressive strength in N/mm² (or MPa) at 28 days, measured on standard 150 mm cubes. For example, M20 means concrete with 28-day characteristic cube compressive strength of 20 N/mm².
