Brick strength classification: According to common building materials standards, what is the minimum compressive strength specified for second-class (II class) burnt clay bricks?
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A75 kg/cm²
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B90 kg/cm²
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C100 kg/cm²
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D120 kg/cm²
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E150 kg/cm²
Answer
Correct Answer: 75 kg/cm²
Explanation
Introduction / Context:Bricks are graded by compressive strength, dimensional tolerances, and appearance. Knowing the minimum strength helps designers specify appropriate classes for load-bearing or non-load-bearing masonry.
Given Data / Assumptions:
- Question refers to typical textbook/MCQ values for second-class bricks.
- Units are in kg/cm² (1 MPa ≈ 10.197 kg/cm²).
Concept / Approach:Common exam references state that first-class bricks have a compressive strength around 100–105 kg/cm² or higher, while second-class bricks are typically specified at about 70–75 kg/cm² minimum. Hence among the given choices, 75 kg/cm² is the accepted minimum for II class bricks.
Step-by-Step Solution:
Recall standard values: I class ≈ 100 kg/cm²+, II class ≈ 70–75 kg/cm².Match options to the conventional minimum → 75 kg/cm².Select 75 kg/cm² as the minimum for II class bricks.Verification / Alternative check:Many handbooks and solved question banks align II class bricks near 7 MPa (≈ 71–75 kg/cm²), confirming the choice.
Why Other Options Are Wrong:
- 90/100/120/150 kg/cm²: these values correspond to first-class or special bricks; too high for the minimum of II class.
Common Pitfalls:
- Mixing up MPa and kg/cm² leading to numerical mis-selection.
- Assuming the same minimum for both I and II class bricks.
Final Answer:75 kg/cm²