Crushing strength of first class bricks should not be less than
🧱 Understanding Brick Classification
Bricks are classified into different classes (First, Second, Third, etc.) based on their physical properties like strength, water absorption, shape, and appearance. Crushing strength is one of the most important properties, as it determines the brick's ability to withstand loads, making it suitable for different types of construction work.
🔬 Detailed Analysis of Crushing Strength Values
C. 100 kg/cm²
This is the correct answer. For a brick to be classified as a First Class Brick, its crushing strength must not be less than 100 kg/cm². In modern SI units, this is equivalent to approximately 10 N/mm² or 10 MPa. First-class bricks are used for high-quality, permanent, and load-bearing structures.
B. 70 kg/cm²
This is the minimum requirement for a Second Class Brick (approximately 7 N/mm²). These bricks are used for less important works or for the inner parts of walls that are plastered.
A. 35 kg/cm²
This is the minimum requirement for a Third Class Brick (approximately 3.5 N/mm²). These bricks are of low quality and are only used for temporary structures or in places where they are not subjected to significant loads or harsh weather.
D. 150 kg/cm²
While some high-quality bricks can exceed this strength, 150 kg/cm² (15 N/mm²) is not the minimum standard for first-class bricks. It represents a very high strength, often found in engineering bricks or heavy-duty bricks.
📊 Summary: Classification of Bricks (As per Indian Standards)
| Property | First Class | Second Class | Third Class |
|---|---|---|---|
| Crushing Strength | ≥ 100 kg/cm² (10 N/mm²) | ≥ 70 kg/cm² (7 N/mm²) | ≥ 35 kg/cm² (3.5 N/mm²) |
| Water Absorption (24hr) | ≤ 20% of its dry weight | ≤ 22% of its dry weight | ≤ 25% of its dry weight |
| Shape & Appearance | Uniform size, sharp edges, smooth surface | Slight irregularities allowed | Irregular shape, distorted |
| Soundness | Clear metallic ringing sound | Clear ringing sound | Dull sound |
💡 Study Tips
- The 100 Mark: Think of 100 as the "passing mark" to get into the First Class.
- Remember the 35, 70, 100 Sequence: The minimum strengths for Third, Second, and First class bricks follow a rough doubling pattern (35 -> 70 -> ~100), making it easier to remember the different levels.
- Units Matter: Be comfortable with both kg/cm² and N/mm². Remember that 10 kg/cm² is approximately 1 N/mm² (or 1 MPa).