Comprehensive 100-question multiple-choice bank on Concrete Technology, complete with answer keys
Section 1: Cement & Hydration (Questions 1–20)
1. Which Bogue’s compound is responsible for the initial setting time of cement?
A) Tricalcium silicate (C₃S)
B) Dicalcium silicate (C₂S)
C) Tricalcium aluminate (C₃A)
D) Tetracalcium aluminoferrite (C₄AF)
Answer: C
2. Which compound contributes to the long-term progressive strength of concrete?
A) C₃S
B) C₂S
C) C₃A
D) C₄AF
Answer: B
3. Gypsum is added during cement manufacturing to:
A) Increase strength
B) Retard the setting time
C) Accelerate the setting time
D) Reduce heat of hydration
Answer: B
4. The normal consistency of ordinary Portland cement is generally around:
A) 10% to 15%
B) 20% to 30%
C) 40% to 50%
D) 60% to 70%
Answer: B
5. Soundness of cement is tested to detect the presence of excess:
A) Alumina
B) Iron oxide
C) Free lime and magnesia
D) Silica
Answer: C
6. Which apparatus is used to perform the soundness test of cement?
A) Vicat apparatus
B) Le Chatelier apparatus
C) Blaine’s air permeability apparatus
D) Slump cone
Answer: B
7. The initial setting time for ordinary Portland cement should not be less than:
A) 10 minutes
B) 30 minutes
C) 60 minutes
D) 600 minutes
Answer: B
8. The final setting time of Ordinary Portland Cement should not exceed:
A) 1 hour
B) 5 hours
C) 10 hours
D) 24 hours
Answer: C
9. Blaine’s air permeability apparatus is used to measure:
A) Consistency
B) Fineness
C) Soundness
D) Compressive strength
Answer: B
10. White cement contains a very low percentage of:
A) Silica
B) Alumina
C) Iron oxide
D) Magnesium oxide
Answer: C
11. Hydrophobic cement is produced by grinding OPC clinker with:
A) Oleic acid
B) Calcium chloride
C) Gypsum
D) Fly ash
Answer: A
12. For marine structures, which type of cement is most preferable?
A) Low heat cement
B) Blast furnace slag cement
C) Rapid hardening cement
D) High alumina cement
Answer: B
13. Rapid hardening cement attains early strength due to an increased content of:
A) C₂S
B) C₃S
C) Gypsum
D) Fly ash
Answer: B
14. The specific gravity of Ordinary Portland Cement is generally around:
A) 2.65
B) 3.15
C) 1.50
D) 4.20
Answer: B
15. Heat of hydration is highest for which Bogue’s compound?
A) C₃A
B) C₃S
C) C₂S
D) C₄AF
Answer: A
16. Calcium chloride (CaCl₂) acts in concrete as an:
A) Retarder
B) Air-entraining agent
C) Accelerator
D) Plasticizer
Answer: C
17. Flash set of cement paste is caused by the premium presence of:
A) C₃S
B) C₂S
C) C₃A
D) C₄AF
Answer: C
18. Which cement is recommended for mass concrete dams?
A) Rapid hardening cement
B) Low heat cement
C) High alumina cement
D) Sulphate resisting cement
Answer: B
19. One bag of Portland cement weighing 50 kg has a volume of approximately:
A) 25 liters
B) 34.5 liters
C) 50 liters
D) 42.5 liters
Answer: B
20. The main constituent of cement is:
A) Silica
B) Lime
C) Alumina
D) Iron oxide
Answer: B
Section 2: Aggregates (Questions 21–40)
21. Aggregates that pass through a 4.75 mm sieve are classified as:
A) Coarse aggregate
B) Fine aggregate
C) Flaky aggregate
D) Elongated aggregate
Answer: B
22. Bulking of sand is maximum when the moisture content is around:
A) 1% to 2%
B) 4% to 6%
C) 10% to 12%
D) 15% to 20%
Answer: B
23. Bulking of sand occurs due to:
A) Surface tension of water film
B) Capillary action
C) Viscosity of water
D) Chemical reaction
Answer: A
24. Which aggregate shape provides the best workability with minimum water?
A) Angular
B) Flaky
C) Rounded
D) Elongated
Answer: C
25. Which aggregate shape offers the highest bond strength with cement paste?
A) Rounded
B) Angular
C) Irregular
D) Flaky
Answer: B
26. An aggregate is classified as flaky if its minimum dimension is less than:
A) 0.6 times mean dimension
B) 1.8 times mean dimension
C) 0.8 times mean dimension
D) 0.5 times mean dimension
Answer: A
27. An aggregate is classified as elongated if its maximum dimension is greater than:
A) 0.6 times mean dimension
B) 1.2 times mean dimension
C) 1.8 times mean dimension
D) 2.0 times mean dimension
Answer: C
28. Los Angeles machine is used to test aggregates for:
A) Crushing value
B) Impact value
C) Abrasion resistance
D) Soundness
Answer: C
29. Aggregate impact value measures which property?
A) Toughness
B) Hardness
C) Crushing strength
D) Durability
Answer: A
30. Aggregate crushing value measures which property?
A) Resistance to wear
B) Resistance to impact
C) Resistance to compressive forces
D) Resistance to weathering
Answer: C [1, 2]
31. For heavy-duty concrete floors, the aggregate abrasion value should not exceed:
A) 30%
B) 45%
C) 50%
D) 60%
Answer: A
32. Fineness modulus of sand tells us about its:
A) Average particle size
B) Shape
C) Specific gravity
D) Grading curve gap
Answer: A
33. Fine sand has a fineness modulus in the range of:
A) 2.2 – 2.6
B) 2.6 – 2.9
C) 2.9 – 3.2
D) 3.2 – 4.0
Answer: A
34. Coarse sand has a fineness modulus in the range of:
A) 1.5 – 2.1
B) 2.2 – 2.6
C) 2.6 – 2.9
D) 2.9 – 3.2
Answer: D
35. If the fineness modulus of an aggregate is 7.0, it can be classified as:
A) Fine sand
B) Coarse sand
C) Coarse aggregate
D) All-in aggregate
Answer: C
36. Alkaline-aggregate reaction occurs due to the presence of reactive silica in:
A) Water
B) Admixtures
C) Cement matrix
D) Aggregates
Answer: D [3]
37. Sea sand should not be used in reinforced concrete because it causes:
A) Slow setting
B) Corrosion of steel reinforcement
C) Excess shrinkage
D) High workability
Answer: B
38. Moisture content trapped in the pores of an aggregate is called:
A) Free moisture
B) Absorbed moisture
C) Surface moisture
D) Effective water
Answer: B
39. Light-weight aggregates are used to manufacture concrete with:
A) Ultra-high strength
B) Thermal insulation properties
C) High abrasion resistance
D) Low shrinkage
Answer: B
40. Soundness test of aggregates evaluates their resistance to:
A) Mechanical impact
B) Gradual loading
C) Weathering and volume change
D) Continuous scraping
Answer: C
Section 3: Fresh Concrete & Workability (Questions 41–60)
41. Workability of concrete is directly proportional to:
A) Aggregate-cement ratio
B) Time of transit
C) Grading of aggregate
D) Flakiness index
Answer: C
42. The slump test of concrete is a measure of its:
A) Compressive strength
B) Tensile strength
C) Consistency and workability
D) Durability
Answer: C
43. For high-rise pumping concrete, which type of slump is desirable?
A) Collapse slump
B) Shear slump
C) True slump
D) Zero slump
Answer: C
44. If the slump of a concrete mix is 0–25 mm, its workability is:
A) Very low
B) Low
C) Medium
D) High
Answer: A
45. For heavily reinforced sections without vibration, the workability should be:
A) Low
B) Medium
C) High
D) Very high
Answer: C
46. Compacting factor test is more accurate than slump test for mixes with:
A) Very high workability
B) Low to very low workability
C) High water cement ratio
D) Large size aggregate
Answer: B
47. A compacting factor of 0.92 indicates a workability level of:
A) Low
B) Medium
C) High
D) Very high
Answer: B
48. Vee-Bee consistometer test measures workability in terms of:
A) Millimeters
B) Percentage
C) Seconds
D) Kilograms
Answer: C
49. Separation of coarse aggregates from the mortar matrix in fresh concrete is called:
A) Bleeding
B) Segregation
C) Creep
D) Shrinkage
Answer: B
50. Separation of water from a freshly mixed concrete mass is known as:
A) Segregation
B) Bleeding
C) Hydration
D) Laitance
Answer: B
51. Laitance is defined as:
A) Coarse aggregate settling at the bottom
B) A milky, slimy layer of cement and water at the top
C) Evaporation of water during curing
D) Void formation inside concrete
Answer: B
52. Workability can be safely increased without altering the water-cement ratio by adding:
A) More cement
B) Plasticizers or superplasticizers
C) Calcium chloride
D) Fine sand
Answer: B
53. Internal friction between concrete components can be minimized by using:
A) Elongated aggregates
B) Angular aggregates
C) Well-graded rounded aggregates
D) Crushed stone dust
Answer: C
54. Harshness in concrete mixes can be caused due to:
A) Excess of fine sand
B) Insufficient quantity of cement paste
C) High water-cement ratio
D) Use of plasticizers
Answer: B
55. Hand mixing of concrete requires an extra cement addition of:
A) 5%
B) 10%
C) 15%
D) 20%
Answer: B
56. Ready Mix Concrete (RMC) is preferred over site-mix concrete because of:
A) Lower cost
B) Higher quality control and uniformity
C) Faster manual placement
D) No need for transit mixers
Answer: B
57. The maximum time limit to discharge concrete from a transit mixer without retarding agents is:
A) 30 minutes
B) 60 minutes
C) 90 minutes
D) 120 minutes
Answer: C
58. Segregation is highly likely to happen if concrete is dropped from a height exceeding:
A) 0.5 meter
B) 1.0 meter
C) 1.5 meters
D) 3.0 meters
Answer: C [4]
59. Over-vibration of fresh concrete leads directly to:
A) Honeycombing
B) High porosity
C) Segregation and bleeding
D) Accelerated setting
Answer: C
60. The primary purpose of compacting fresh concrete is to:
A) Remove entrapped air
B) Add water to dry patches
C) Separate the aggregates
D) Increase setting speed
Answer: A
Section 4: Admixtures & Mix Design (Questions 61–80)
61. Which type of admixture is used to entrain microscopic air bubbles in concrete?
A) Plasticizers
B) Accelerators
C) Air-entraining agents
D) Mineral admixtures
Answer: C
62. Air entrainment in concrete increases its resistance to:
A) Abrasion
B) Freezing and thawing cycles
C) High temperatures
D) Creep
Answer: B
63. Sugar acts as a concrete:
A) Accelerator
B) Retarder
C) Air-entraining agent
D) Coloring agent
Answer: B
64. Superplasticizers can reduce water requirements in a concrete mix by up to:
A) 5%
B) 10%
C) 30%
D) 50%
Answer: C
65. Silica fume is a pozzolanic material that consists primarily of:
A) Amorphous silicon dioxide
B) Calcium oxide
C) Alumina oxide
D) Iron oxide
Answer: A
66. Fly ash is a byproduct obtained from:
A) Blast furnaces
B) Coal-fired power plants
C) Volcanic eruptions
D) Cement kilns
Answer: B
67. Adding fly ash to concrete generally leads to:
A) Higher early strength
B) Increased heat of hydration
C) Improved long-term strength and durability
D) Decreased workability
Answer: C
68. In concrete mix design, the target mean strength ($f_{cm}$) is calculated as:
A) $f_{ck} + 1.65\sigma$
B) $f_{ck} – 1.65\sigma$
C) $f_{ck} + \sigma$
D) $1.65 f_{ck}$
Answer: A
69. The term “$f_{ck}$” in mix design standard formulas refers to:
A) Mean strength
B) Target strength
C) Characteristic compressive strength
D) Flexural strength
Answer: C
70. Characteristic strength is defined as that value below which not more than ____ of test results are expected to fall:
A) 1%
B) 5%
C) 10%
D) 50%
Answer: B
71. Lowering the water-cement ratio in a concrete mix results in:
A) Decreased strength and increased permeability
B) Increased strength and decreased permeability
C) High workability
D) Increased bleeding
Answer: B
72. Abram’s law establishes a mathematical relationship between strength and:
A) Aggregate size
B) Water-cement ratio
C) Curing period
D) Sand content
Answer: B
73. In concrete mix designations like M25, the letter “M” stands for Mix and “25” represents:
A) 28-day characteristic cube compressive strength in N/mm²
B) 7-day tensile strength in N/mm²
C) 28-day flexural strength in MPa
D) Nominal volume ratio
Answer: A
74. Ordinary concrete grades according to standard structural classifications include:
A) M10 to M20
B) M25 to M55
C) M60 to M80
D) M100+
Answer: A
75. Standard concrete grades range from:
A) M10 to M20
B) M25 to M60
C) M65 to M100
D) Above M100
Answer: B
76. Nominal mix concrete is generally permitted for grades up to:
A) M20
B) M35
C) M50
D) M75
Answer: A
77. The nominal volume ratio of an M15 concrete mix is approximately:
A) 1:1:2
B) 1:1.5:3
C) 1:2:4
D) 1:3:6
Answer: C
78. The nominal volume ratio of an M20 concrete mix is:
A) 1:1:2
B) 1:1.5:3
C) 1:2:4
D) 1:3:6
Answer: B
79. Rice husk ash is classified as a:
A) Chemical admixture
B) Accelerating agent
C) Mineral pozzolanic admixture
D) Air-entraining agent
Answer: C
80. Which of the following reduces plastic shrinkage cracks in fresh concrete surfaces?
A) Retarders
B) Polypropylene fibers
C) Heavy vibrations
D) Extra water spraying
Answer: B [5]
Section 5: Hardened Properties, Testing & Durability (Questions 81–100)
81. Standard size of a concrete cube specimen used for compressive testing is:
A) 50 × 50 × 50 mm
B) 100 × 100 × 100 mm
C) 150 × 150 × 150 mm
D) 200 × 200 × 200 mm
Answer: C
82. Cylinder strength of concrete is usually assumed to be about _____ of cube strength:
A) 50%
B) 80%
C) 100%
D) 125%
Answer: B
83. Concrete compressive strength tests are universally performed after a curing period of:
A) 3 days
B) 7 days
C) 14 days
D) 28 days
Answer: D
84. Flexural strength of concrete is determined using which standard test?
A) Split cylinder test
B) Third-point loading test on a prism beam
C) Compression test machine
D) Core cutter method
Answer: B
85. The modulus of elasticity of concrete ($E_c$) can be estimated as:
A) $5000 \sqrt{f_{ck}}$
B) $5700 \sqrt{f_{ck}}$
C) $7000 \sqrt{f_{ck}}$
D) $0.7 \sqrt{f_{ck}}$
Answer: A
86. Continuous gradual deformation of concrete under a sustained constant load is known as:
A) Plastic shrinkage
B) Elastic strain
C) Creep
D) Fatigue
Answer: C
87. Modulus of rupture of concrete gives a direct indication of its:
A) Direct tensile strength
B) Flexural tensile strength
C) Direct compressive strength
D) Shear strength
Answer: B
88. Split tensile strength of concrete is evaluated using a specimen shaped as a:
A) Cube
B) Prism
C) Cylinder
D) Sphere
Answer: C [6]
89. Non-Destructive Testing (NDT) includes which of the following tools?
A) Universal testing machine
B) Rebound hammer test
C) Split cylinder rig
D) Core testing barrel
Answer: B [7]
90. Rebound hammer test measures which specific property of hardened concrete?
A) Internal tensile stress
B) Surface hardness
C) Modulus of elasticity
D) Depth of voids
Answer: B
91. Ultrasonic Pulse Velocity (UPV) testing evaluates concrete quality based on:
A) Electrical resistance
B) Sound wave velocity through the concrete mass
C) Color changes
D) Chemical leaching
Answer: B
92. If UPV test results show a pulse velocity above 4.5 km/s, the concrete quality is:
A) Excellent
B) Good
C) Medium
D) Poor
Answer: A
93. Carbonation of concrete happens due to its reaction with:
A) Carbon monoxide
B) Atmospheric carbon dioxide (CO₂)
C) Carbonic acid in groundwater
D) Hydrocarbons
Answer: B
94. Carbonation causes a drop in concrete pH, which primarily leads to:
A) Increased sulfate attack
B) Corrosion of embedded steel reinforcement
C) Discoloration of surfaces
D) Aggregate dissolving
Answer: B
95. Curing of concrete is done to:
A) Prevent evaporation of water needed for hydration
B) Bleed out excess water
C) Reduce overall volume
D) Darken the color
Answer: A
96. Minimum period of curing for concrete using OPC under normal weather conditions is:
A) 3 days
B) 7 days
C) 14 days
D) 28 days
Answer: B
97. Sulfate attack on concrete chemically damages the structure by forming:
A) Calcium silicate hydrate
B) Ettringite
C) Calcium hydroxide
D) Sodium chloride
Answer: B
98. Pop-outs on concrete surfaces are generally caused by:
A) Alkali-silica gel expansion or unsound aggregates
B) Lack of initial slump
C) Excessive water-cement ratio
D) Under-vibration
Answer: A
99. Honeycombing in concrete structures is a defect caused due to:
A) Excess water in the mix
B) Poor compaction or narrow spacing between rebars
C) Use of rapid hardening cement
D) Extended curing periods
Answer: B
100. The phenomenon of structural cracking due to repetitive cyclic loading is called:
A) Creep
B) Fatigue
C) Elasticity
D) Carbonation
Answer: B
