Building Materials – Bricks & Clay Products for JE Exam | Concepts, MCQs & PYQs

🔹 1. Concept Explanation (Exam-Focused)

Composition of Brick Earth

Good brick earth is not pure clay. Questions often ask ideal percentage ranges.

• Alumina (20–30%) – Provides plasticity.
  Excess → shrinkage & cracks
• Silica (50–60%) – Prevents shrinkage & warping.
  Excess → brittle bricks
• Lime (5–10%) – Helps fusion at burning stage.
  Excess → lime blowing
• Iron Oxide (5–6%) – Gives red color & strength
• Magnesia (≤1%) – Yellow tint; excess reduces strength

👉 Exam framing: Match-the-following, assertion–reason, % based MCQs.

Manufacturing Process of Bricks

Usually asked in correct sequence.

1. Preparation of clay – Unsoiling → Digging → Weathering → Blending → Tempering
2. Moulding
   • Hand moulded (ground / table moulded)
   • Machine moulded (wire cut) – more uniform
3. Drying – 7–14 days, shrinkage ≈ 8–10%
4. Burning – 900–1100°C in kilns

Kilns: Clamp (temporary), Bull’s Trench Kiln (BTK – most common in India), Hoffmann Kiln

Classification of Bricks

• First Class: Table moulded, kiln burnt, smooth surface
• Second Class: Ground moulded, slight irregularities
• Third Class: Under-burnt, low strength (temporary works)
• Fourth Class: Over-burnt, vitrified (used as aggregate)

👉 SSC JE favorite: Identify use based on class.

Tests on Bricks (IS 3495)

1. Compressive Strength Test
2. Water Absorption Test – ≤20% (1st class)
3. Efflorescence Test – White patches due to soluble salts
4. Dimension Test

Clay Products

• Tiles: Roofing, flooring, wall tiles
• Stoneware pipes: Sewer lines
• Terracotta: Decorative work
• Fire clay products: Refractory bricks

🔹 2. Important Formulas (Highly Repeated)

Compressive Strength of Brick

 

Where:
= Compressive strength (N/mm²)
= Load at failure (N)
= Loaded area (mm²)

⭐ Most repeated formula in SSC JE

Water Absorption

 

= Dry weight
= Wet weight

🔹 3. Short Notes / One-Liners (Last-Day Revision)

• Standard brick size (India): 190 × 90 × 90 mm
• Nominal size with mortar: 200 × 100 × 100 mm
• Frog depth ≈ 10–20 mm
• Bricks are strong in compression, weak in tension
• Efflorescence is not a structural defect

Mnemonic (Composition):
A–S–L–I–M → Alumina, Silica, Lime, Iron oxide, Magnesia

🔹 4. PYQ Patterns (SSC JE / RRB JE)

• % composition of brick earth (very frequent)
• Max water absorption limit
• Identify kiln type
• Wrong statement on efflorescence
• Numerical on compressive strength

⚠️ Trap: Confusing nominal size with actual size

🔹 5. Solved Examples

Numerical Example

A brick fails at 180 kN. Area = 190 × 90 mm².

 

✔ Suitable for First Class Brick

Conceptual Example

Q: Why silica is necessary in brick earth?
Ans: To prevent excessive shrinkage and cracking during drying.

🔹 6. MCQs (Exam Level – 30 Questions)

1. Maximum water absorption for first class bricks is:
   A. 15% B. 20% C. 25% D. 30%
   ✅ Ans: B – IS limit
2. Color of brick is mainly due to:
   A. Alumina B. Lime C. Iron oxide D. Silica
   ✅ Ans: C
3. Frog in brick is provided to:
   A. Reduce weight
   B. Increase bond with mortar
   C. Decoration
   D. Reduce cost
   ✅ Ans: B
4. Over-burnt bricks are used as:
   A. Facing bricks
   B. Load bearing
   C. Aggregate
   D. Flooring
   ✅ Ans: C
5. The main function of lime in brick earth is to
6. Provide plasticity
   B. Prevent shrinkage
   C. Help fusion of particles
   D. Impart color

✅ Answer: C
📝 Explanation: Lime acts as a flux, helping silica to fuse during burning.

6. Excess alumina in brick earth causes
7. Brittleness
   B. Warping
   C. Cracks on drying
   D. Yellow color

✅ Answer: C
📝 Explanation: Alumina increases plasticity; excess leads to shrinkage & cracks.

7. Standard depth of frog in brick is
8. 5 mm
   B. 10–20 mm
   C. 25 mm
   D. 30 mm

✅ Answer: B
📝 Explanation: Frog depth generally ranges between 10–20 mm.

8. Which kiln is most commonly used in India?
9. Clamp kiln
   B. Hoffmann kiln
   C. Bull’s trench kiln
   D. Down-draught kiln

✅ Answer: C
📝 Explanation: BTK is widely used due to continuous operation and fuel economy.

9. Nominal size of brick with mortar is
10. 190 × 90 × 90 mm
    B. 200 × 100 × 100 mm
    C. 230 × 110 × 75 mm
    D. 210 × 100 × 100 mm

✅ Answer: B
📝 Explanation: Nominal size includes 10 mm mortar thickness.

10. First-class bricks are generally
11. Under-burnt
    B. Over-burnt
    C. Table moulded and kiln burnt
    D. Sun dried

✅ Answer: C
📝 Explanation: First-class bricks are uniform, strong, and well-burnt.

11. Efflorescence in bricks is caused by
12. Alumina
    B. Iron oxide
    C. Soluble salts
    D. Excess silica

✅ Answer: C
📝 Explanation: White patches are due to soluble salts migrating to the surface.

12. Maximum permissible water absorption for first-class bricks is
13. 15%
    B. 18%
    C. 20%
    D. 25%

✅ Answer: C
📝 Explanation: As per IS code, it should not exceed 20%.

13. Bricks are strong in
14. Tension
    B. Compression
    C. Bending
    D. Shear

✅ Answer: B
📝 Explanation: Bricks have high compressive strength, negligible tensile strength.

14. Drying of bricks is done to
15. Increase strength
    B. Reduce moisture before burning
    C. Improve color
    D. Increase density

✅ Answer: B
📝 Explanation: Drying prevents cracks during burning.

15. Temperature range for burning bricks is
16. 500–700°C
    B. 700–900°C
    C. 900–1100°C
    D. 1100–1300°C

✅ Answer: C
📝 Explanation: Proper vitrification occurs between 900–1100°C.

16. Over-burnt bricks are generally
17. Soft and weak
    B. Used for load-bearing work
    C. Brittle and vitrified
    D. Under-strength

✅ Answer: C
📝 Explanation: Over-burning causes vitrification, making bricks brittle.

17. Which test determines crushing strength of bricks?
18. Water absorption test
    B. Efflorescence test
    C. Compression test
    D. Dimension test

✅ Answer: C
📝 Explanation: Crushing strength is obtained from compressive strength test.

18. Shrinkage during drying of bricks is approximately
19. 2–3%
    B. 4–5%
    C. 8–10%
    D. 12–15%

✅ Answer: C
📝 Explanation: Drying shrinkage is typically 8–10%.

19. Which clay product is used for sewer lines?
20. Terracotta
    B. Fire clay
    C. Stoneware pipes
    D. Roofing tiles

✅ Answer: C
📝 Explanation: Stoneware pipes are dense and impervious.

20. Iron oxide in brick earth mainly
21. Improves plasticity
    B. Reduces shrinkage
    C. Gives red color & strength
    D. Prevents efflorescence

✅ Answer: C
📝 Explanation: Iron oxide contributes to color and hardness.

21. Fourth-class bricks are suitable for
22. Face work
    B. Load-bearing walls
    C. Aggregates in concrete
    D. Flooring

✅ Answer: C
📝 Explanation: Over-burnt bricks are crushed and used as aggregate.

22. Which brick moulding method gives uniform size?
23. Ground moulding
    B. Table moulding
    C. Hand moulding
    D. Machine moulding

✅ Answer: D
📝 Explanation: Machine moulding (wire-cut) ensures uniformity.

23. The presence of magnesia in excess causes
24. Cracks
    B. Loss of strength
    C. Yellow tint
    D. Black core

✅ Answer: C
📝 Explanation: Magnesia imparts yellowish color.

24. Bricks used for refractory lining are made of
25. Silica clay
    B. Fire clay
    C. Ordinary clay
    D. Lime clay

✅ Answer: B
📝 Explanation: Fire clay bricks resist high temperatures.

25. Which is NOT a test on bricks?
26. Hardness test
    B. Compression test
    C. Water absorption test
    D. Efflorescence test

✅ Answer: A
📝 Explanation: Hardness test is not standard as per IS 3495.

26. Under-burnt bricks are classified as
27. First class
    B. Second class
    C. Third class
    D. Fourth class

✅ Answer: C
📝 Explanation: Third-class bricks are under-burnt and weak.

27. Clay used for tiles should be
28. Highly plastic
    B. Low plastic
    C. Non-plastic
    D. Sandy

✅ Answer: A
📝 Explanation: High plasticity ensures proper shaping of tiles.

28. Efflorescence mainly affects
29. Strength
    B. Durability
    C. Appearance
    D. Bond strength

✅ Answer: C
📝 Explanation: It is not a structural defect, only aesthetic.

29. Black core in bricks is due to
30. Excess lime
    B. Incomplete oxidation
    C. Excess alumina
    D. Rapid cooling

✅ Answer: B
📝 Explanation: Inadequate oxygen during burning causes black core.

30. Which is a temporary type of brick kiln?
31. Hoffmann kiln
    B. BTK
    C. Clamp kiln
    D. Tunnel kiln

✅ Answer: C
📝 Explanation: Clamp kiln is temporary and inefficient.