Topics covered: Brick, Cement, Concrete: Easy to moderate level
Construction Materials Topic-wise Questions for PWD JE Exam
Topic: Bricks
1. The standard size of modular brick as per IS is —
Answer: A
The standard size of modular brick as per Indian Standards (IS) is 190 mm × 90 mm × 90 mm. This size includes mortar thickness (10mm) in each dimension, making the actual brick size 190 mm × 90 mm × 90 mm.
2. The compressive strength of first-class bricks should not be less than —
Answer: C
First-class bricks must have a minimum compressive strength of 7 N/mm² (70 kg/cm²) as per Indian standards. These high-quality bricks are used for permanent structures and have uniform color and shape.
3. Efflorescence in bricks is caused due to —
Answer: A
Efflorescence is the white powdery deposit on brick surfaces caused by soluble alkalies (mainly sodium and potassium salts) present in bricks. When water evaporates from the brick surface, these salts crystallize and appear as white patches.
4. The minimum water absorption for first-class bricks after 24 hours immersion should not exceed —
Answer: C
First-class bricks should have water absorption between 12-15% of their dry weight when immersed in cold water for 24 hours. Higher absorption indicates poor quality bricks that may lead to dampness issues.
5. The process of kneading brick earth with water to make it plastic is called —
Answer: B
Tempering is the process of thoroughly mixing clay with water to make it homogeneous and plastic. Proper tempering ensures uniform quality and strength in bricks. It's typically done for 3-4 days.
6. Which of the following is NOT a type of brick bond?
Answer: D
Mortar bond is not a type of brick bond. Common brick bonds include English bond (alternate headers and stretchers), Flemish bond (alternate headers and stretchers in each course), and Rat-trap bond (creating cavity within wall).
7. The percentage of alumina in good brick earth should be —
Answer: B
Good brick earth should contain 20-30% alumina. Alumina provides plasticity to the clay for molding but excess alumina (over 30%) causes cracks during drying and burning.
8. Which of the following tests is used to check the soundness of bricks?
Answer: D
Brick soundness is checked by multiple tests: Efflorescence test (for salts), Hardness test (scratch resistance), and Soundness test (metallic ringing sound when struck). Good bricks should pass all these tests.
9. The temperature range for burning bricks in kilns is —
Answer: C
Bricks are typically burnt at 900-1200°C in kilns. At this temperature, clay particles fuse together giving bricks their strength. Under-burnt bricks are soft while over-burnt bricks become brittle.
10. Which of the following is NOT a advantage of brick masonry?
Answer: C
Bricks have poor tensile strength (only about 10-20% of their compressive strength). This is why reinforced concrete is used where tensile strength is required. Bricks excel in compression, fire resistance, and thermal properties.
Topic: Cement
11. The main ingredient responsible for early strength of cement is —
Answer: A
Tricalcium Silicate (C3S) is the compound that hydrates quickly and provides early strength (1-7 days) to cement. It constitutes about 45-60% of ordinary Portland cement and generates more heat during hydration.
12. Fineness of cement is tested by —
Answer: C
Fineness of cement is tested by sieve test (using 90 micron sieve) or by air permeability method (Blaine's apparatus). Finer cement provides better workability and early strength but requires more water and may shrink more.
13. The setting time of ordinary Portland cement is tested using —
Answer: B
The Vicat apparatus is used to determine initial and final setting times of cement. Initial setting time is when the needle penetrates 33-35mm from top, and final setting time is when the needle makes an impression but doesn't penetrate.
14. The compound responsible for flash set in cement is —
Answer: C
Tricalcium Aluminate (C3A) causes flash set (rapid hardening immediately after mixing). Gypsum is added to cement to control C3A's rapid reaction. C3A constitutes 8-12% of OPC and contributes to early strength but reduces sulfate resistance.
15. The standard consistency of ordinary Portland cement is about —
Answer: B
Standard consistency of OPC is typically 25-30% water by weight of cement. This is the water content required to allow the Vicat plunger to penetrate to 5-7mm from the bottom in consistency test.
16. Which cement type is most suitable for marine structures?
Answer: D
Sulfate Resisting Cement (SRC) is most suitable for marine structures as it resists sulfate attack from seawater. It has reduced C3A content (<5%) and is also used in foundations where sulfate salts are present in soil/water.
17. The initial setting time of OPC as per IS code should not be less than —
Answer: B
As per IS 269, the initial setting time of OPC should not be less than 30 minutes to allow sufficient time for mixing and placing. The final setting time should not exceed 600 minutes (10 hours).
18. The main function of gypsum in cement is to —
Answer: B
Gypsum (3-5%) is added during cement manufacturing to retard the setting time by controlling the rapid hydration of C3A. Without gypsum, cement would set almost immediately after mixing with water.
19. Which test determines the soundness of cement?
Answer: B
Le Chatelier apparatus test determines cement soundness (ability to resist volume change). Unsound cement expands significantly when tested. Autoclave test is also used for soundness testing.
20. The approximate percentage of lime in ordinary Portland cement is —
Answer: D
OPC contains about 60-67% lime (CaO) by weight. Lime is the principal constituent that forms calcium silicates and aluminates during clinker formation. Excess lime causes unsoundness while deficiency reduces strength.
Topic: Concrete
21. The ratio of water to cement for complete hydration of cement is approximately —
Answer: A
The water-cement ratio needed for complete hydration is about 0.25 by weight (25% of cement weight). However, practical mixes use higher ratios (0.4-0.6) for workability, with excess water evaporating and leaving pores.
22. In concrete, the function of water is to —
Answer: C
Water in concrete primarily facilitates the chemical reaction (hydration) between cement and water that binds the mixture. While it affects strength and workability, its primary role is enabling the hydration process.
23. The initial setting time of Ordinary Portland Cement should not be less than —
Answer: B
As per IS codes, OPC must have initial setting time ≥ 30 minutes to allow sufficient time for mixing, transporting, and placing concrete. Final setting time should be ≤ 600 minutes (10 hours).
24. The maximum size of coarse aggregate used in RCC work is —
Answer: B
For RCC work, maximum aggregate size is limited to 20mm (or 1/4th of minimum member dimension). Larger aggregates (40mm) are used in mass concrete. Smaller aggregates improve workability but require more cement.
25. The concrete mix ratio of M20 grade is —
Answer: A
M20 concrete has a mix ratio of 1:1.5:3 (Cement:FineAggregate:CoarseAggregate) by volume. M20 denotes characteristic compressive strength of 20 N/mm² at 28 days. The actual mix design considers w/c ratio, workability, and aggregate grading.
26. Slump test is conducted to measure —
Answer: C
Slump test measures workability (consistency) of fresh concrete. Standard slump values: 25-50mm (low workability), 50-100mm (medium), 100-175mm (high). Not suitable for very dry or very wet mixes.
27. Creep in concrete is —
Answer: B
Creep is time-dependent deformation under sustained load. It continues for years (mostly in first year) and is influenced by w/c ratio, aggregate properties, humidity, and stress level. Higher creep occurs with higher cement content and stress.
28. The minimum grade of concrete for RCC as per IS 456:2000 is —
Answer: C
As per IS 456:2000, minimum grade for RCC is M20 (for mild exposure). For severe exposure conditions (marine, corrosive), minimum grade increases to M30. M20 has characteristic strength of 20 N/mm² at 28 days.
29. The admixture used to retard the setting time of concrete is —
Answer: C
Retarders (like gypsum, sugar) delay setting time, useful in hot weather or long transportation. Common retarders include calcium sulfate, lignosulfonates. They slow C3A hydration without affecting long-term strength.
30. The strength of concrete increases —
Answer: A
Concrete gains about 60-65% of 28-day strength in first 7 days, then rate slows. Strength continues increasing beyond 28 days (about 10-15% more at 3 months) due to ongoing hydration, though design uses 28-day strength.