Building Materials – Bricks & Clay Products | Complete JE Exam Guide

(For SSC JE, RRB JE, OSSC JE – Civil Engineering)

🔶 1. Concept Explanation (Exam-Focused)

1. Composition of Brick Earth

Good brick earth should contain the following constituents in proper proportion:

• Alumina (20–30%)
  Provides plasticity for molding bricks.
  👉 Excess → high shrinkage & cracking

• Silica (50–60%)
  Prevents shrinkage and warping.
  👉 Excess → brittle bricks

• Lime (5–10%)
  Helps fusion during burning and improves strength.
  👉 Excess → lime blowing

• Iron Oxide (5–7%)
  Imparts red color and hardness.

• Magnesia (≤1%)
  Reduces shrinkage, excess gives yellow tint.

📌 Key Theory: Alumina + Silica balance decides brick quality (very common JE question).

2. Manufacturing Process of Bricks

1. Preparation of Clay – Unsoiling, digging, weathering, blending

2. Moulding – Hand moulding / Machine moulding

3. Drying – 7–14 days, removes free moisture

4. Burning – 900°C–1100°C in clamp or kiln

📌 Exam Note:

• Clamp → irregular, cheaper

• Kiln → uniform, better quality bricks

3. Classification of Bricks

• First Class Bricks – Table moulded, kiln burnt, high strength

• Second Class Bricks – Ground moulded, slight defects

• Third Class Bricks – Under-burnt, temporary works

• Fourth Class Bricks – Over-burnt, used as aggregates

4. Tests on Bricks

• Compressive Strength Test

• Water Absorption Test

• Efflorescence Test

• Dimensional Tolerance Test

📌 Water absorption ≤ 20% (first-class bricks)

5. Clay Products

• Tiles – Roofing, flooring

• Stoneware Pipes – Sewer lines

• Fire Clay Bricks – Refractory use

• Terracotta – Architectural works

🔶 2. Important Formulas (JE Repeated)

Compressive Strength of Brick

$$f_c = \frac{P}{A}$$

Where:

• $P$ = Load at failure (N)

• $A$ = Loaded area (mm²)

• $f_c$ = Compressive strength (N/mm²)

📌 JE Trick: “P/A = Power of Brick”

Water Absorption

$$\text{Water Absorption (\%)} = \frac{W_2 – W_1}{W_1} \times 100$$

🔶 3. Short Notes / One-Liners

• Standard brick size (India): 190 × 90 × 90 mm

• Nominal size with mortar: 200 × 100 × 100 mm

• Frog improves bond & strength

• Efflorescence caused due to alkaline salts

• Ideal burning temperature: 1000°C

🔶 4. PYQ Patterns (JE Exams)

✔ Repeated focus on:

• Composition percentages

• Water absorption limits

• Brick dimensions

• First vs Second class bricks
  ✔ Trap: Mixing lime defects with iron oxide effects

🔶 5. Solved Examples

Example 1 (Numerical – SSC JE)

A brick fails at 180 kN. Area = 19,000 mm².
Find compressive strength.

$$f_c = \frac{180000}{19000} = 9.47 \text{ N/mm}^2$$

✅ Answer: 9.47 N/mm²

Example 2 (Conceptual)

Which ingredient gives plasticity to brick earth?
👉 Alumina

🔶 30. MCQs (Exam Level – All in One)

1. Maximum water absorption for first-class bricks is:
A) 15% B) 20% C) 25% D) 30%
✅ Ans: B – IS code limit

2. Red color of brick is due to:
A) Lime B) Silica C) Iron Oxide D) Alumina
✅ Ans: C

3. Over-burnt bricks are used as:
A) Facing bricks B) Aggregate C) Flooring D) Roofing
✅ Ans: B

4. Frog in brick is provided to:
A) Reduce weight
B) Increase strength
C) Improve bond
D) Decorative purpose
✅ Ans: C

5. The plasticity of brick earth is mainly due to

A) Silica
B) Alumina
C) Lime
D) Iron oxide
✅ Answer: B
📝 Alumina provides plasticity required for moulding bricks.

6. Excess of lime in brick earth causes

A) Cracking
B) Warping
C) Lime blowing
D) Loss of strength
✅ Answer: C
📝 Free lime expands after burning, causing disintegration.

7. Which constituent gives hardness and durability to bricks?

A) Alumina
B) Silica
C) Magnesia
D) Lime
✅ Answer: B
📝 Silica prevents shrinkage and adds strength.

8. Standard compressive strength of first-class bricks should not be less than

A) 3.5 N/mm²
B) 7.0 N/mm²
C) 10.5 N/mm²
D) 14.0 N/mm²
✅ Answer: B
📝 IS standard minimum value for first-class bricks.

9. Which brick is used only for temporary structures?

A) First class
B) Second class
C) Third class
D) Fourth class
✅ Answer: C
📝 Third-class bricks are under-burnt and weak.

10. Efflorescence in bricks is caused by

A) Iron oxide
B) Silica
C) Alkali salts
D) Lime
✅ Answer: C
📝 White patches appear due to soluble salts.

11. Water absorption of a good brick should be

A) <10%
B) <15%
C) <20%
D) <25%
✅ Answer: C
📝 As per IS code for first-class bricks.

12. Frog in a brick helps in

A) Reducing cost
B) Increasing strength
C) Improving bond
D) Decoration
✅ Answer: C
📝 Frog improves mortar grip.

13. Which is NOT a clay product?

A) Roofing tiles
B) Stoneware pipes
C) Fire clay bricks
D) Fly ash bricks
✅ Answer: D
📝 Fly ash bricks are not clay-based.

14. The burning temperature of bricks ranges between

A) 400–600°C
B) 600–800°C
C) 900–1100°C
D) 1200–1400°C
✅ Answer: C
📝 Ideal range for proper vitrification.

15. Which kiln gives uniform quality bricks?

A) Clamp
B) Bull’s trench kiln
C) Open fire
D) Temporary kiln
✅ Answer: B
📝 Continuous kilns ensure uniform burning.

16. Over-burnt bricks are generally used for

A) Masonry
B) Flooring
C) Aggregate
D) Facing work
✅ Answer: C
📝 They are brittle and unsuitable for masonry.

17. The nominal size of a brick is

A) 190 × 90 × 90 mm
B) 200 × 100 × 100 mm
C) 230 × 110 × 75 mm
D) 210 × 100 × 100 mm
✅ Answer: B
📝 Includes mortar thickness.

18. Which test checks soluble salts in bricks?

A) Crushing test
B) Water absorption test
C) Efflorescence test
D) Hardness test
✅ Answer: C

19. A brick absorbs 18% water. It is classified as

A) First class
B) Second class
C) Third class
D) Rejected
✅ Answer: A
📝 Water absorption ≤ 20%.

20. Iron oxide in brick earth provides

A) Strength
B) Plasticity
C) Color
D) Durability
✅ Answer: C

21. Excess silica in brick earth makes bricks

A) Weak
B) Brittle
C) Soft
D) Plastic
✅ Answer: B

22. Which defect is caused due to excess alumina?

A) Lime blowing
B) Warping
C) Cracking
D) Efflorescence
✅ Answer: C

23. Stoneware pipes are mainly used for

A) Water supply
B) Sewer lines
C) Gas lines
D) Electrical conduits
✅ Answer: B

24. Fire clay bricks are used for

A) Flooring
B) Roofing
C) Furnace lining
D) Masonry walls
✅ Answer: C

25. Which brick gives maximum strength?

A) Hand-moulded
B) Ground-moulded
C) Table-moulded
D) Sun-dried
✅ Answer: C

26. Dimensional tolerance test checks

A) Strength
B) Shape
C) Size accuracy
D) Durability
✅ Answer: C

27. Under-burnt bricks are

A) Hard and strong
B) Brittle
C) Soft and weak
D) Glassy
✅ Answer: C

28. Magnesia content in brick earth should not exceed

A) 1%
B) 5%
C) 10%
D) 15%
✅ Answer: A

29. Which brick defect shows white patches on surface?

A) Cracking
B) Warping
C) Efflorescence
D) Bloating
✅ Answer: C

30. The test conducted to determine load-carrying capacity of brick is

A) Water absorption
B) Efflorescence
C) Compression test
D) Shape test
✅ Answer: C

✅ Exam Tip (JE Short Trick)

“ASP-LIM” for Brick Earth
Alumina – Plasticity
Silica – Strength
Proportion – Balance
Lime – Fusion
Iron oxide – Color
Magnesia – Shrinkage control

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