The minimum compressive strength of 2nd class bricks should be
💪 Understanding Compressive Strength Classification
The compressive strength of a brick is its ability to resist crushing loads and is a primary indicator of its quality. Indian Standard IS 1077 classifies bricks into different grades or classes based on their minimum average compressive strength. This classification helps engineers select the appropriate brick for different structural applications.
🔬 Detailed Analysis of the Options
A. 70 kg/cm²
This is the correct answer. According to IS 1077, the minimum average compressive strength for a second-class brick should not be less than 70 kg/cm² (which is approximately 7.0 N/mm²). These bricks are considered suitable for most general construction, especially for internal walls that will be plastered.
B. 90 kg/cm²
This is incorrect. A strength of 90 kg/cm² (~9 N/mm²) is well above the minimum for second-class bricks and falls into the range of first-class bricks.
C. 100 kg/cm² & D. 120 kg/cm²
These are incorrect. These values, approximately 10 N/mm² and 12 N/mm² respectively, are the minimum requirements for first-class bricks. First-class bricks are used for high-quality, load-bearing, and exposed masonry work.
📊 Summary: Compressive Strength by Brick Class (IS 1077)
| Brick Class | Minimum Compressive Strength (kg/cm²) | Minimum Compressive Strength (N/mm²) |
|---|---|---|
| First Class | 105 | 10.5 |
| Second Class | 70 | 7.0 |
| Third Class | 35 | 3.5 |
💡 Study Tips
- Memorize the "105-70-35" Rule: These are the key strength values in kg/cm² for 1st, 2nd, and 3rd class bricks, respectively.
- Know the N/mm² Equivalents: Remember the values 10.5, 7.0 (or 7.5), and 3.5 N/mm² as they are also commonly used in exams. The conversion is roughly 1 N/mm² ≈ 10 kg/cm².
- Strength Follows Class: The strength hierarchy is simple: 1st class is the strongest, followed by 2nd, and then 3rd.