Question

For a stone to be used in road work, the coefficient of hardness as worked out from the hardness test should be:

• A. more than 17
• B. 15 to 17
• C. 9 to 15
• D. less than 9

Hint:

For road works, use stones with hardness coefficient>17 to avoid rapid abrasion.

Answer 1

The Correct Option is A

To determine the required hardness coefficient for stones used in road work, we examine standard specifications for road construction materials.

1. Understanding the Hardness Test:
The coefficient of hardness is determined by the Dorry's hardness test, which measures a stone's resistance to wear - a critical property for road aggregates.

2. Standard Requirements for Road Work:
According to Indian Roads Congress (IRC) and international standards:

3. Hardness Coefficient Criteria:
- More than 17: Excellent quality for heavy traffic roads
- 15 to 17: Suitable for normal traffic roads
- 9 to 15: Marginal quality, may require binder enhancement
- Less than 9: Unsuitable for road work

4. Why >17 is Preferred:
- Ensures adequate resistance to abrasion from traffic
- Withstands weathering effects better
- Maintains surface integrity under load
- Reduces maintenance requirements

5. Field Implications:
Stones with hardness coefficient >17: - Are typically igneous rocks like granite, basalt
- Show minimal weight loss in attrition tests
- Have high quartz content
- Provide long-lasting road surfaces

6. Consequences of Lower Hardness:
- Increased rutting and surface wear
- Higher maintenance costs
- Reduced service life
- Potential safety issues

Conclusion:
For optimal performance in road work, the coefficient of hardness should be more than 17.

Final Answer:
The correct option is: more than 17.