The stones obtained by blasting are used as
💥 Understanding Quarrying by Blasting
The method used to extract stone from a quarry determines its initial shape and suitability for different applications. This question focuses on stone obtained by blasting.
Blasting: A quarrying method that uses explosives to break large masses of hard rock away from the quarry face. This process shatters the rock into smaller, irregular, and angular fragments of various sizes.
Stones obtained this way are not suitable for work that requires large, regular blocks (like ashlar masonry), but their properties are ideal for other applications.
🔬 Detailed Analysis of the Uses
Let's examine why the irregular, angular fragments from blasting are perfect for each of the options listed.
A. Ballast in Railways
Railway ballast is the layer of crushed stone that forms the trackbed. Its purpose is to hold the track in place and provide drainage. The sharp, angular shape of blasted stone is essential because the pieces interlock with each other, creating a stable, load-bearing matrix that resists movement under the heavy, dynamic loads of passing trains.
B. Aggregates for Concrete
Aggregates (crushed stone and sand) are a key ingredient in concrete. For the concrete to be strong, there must be a powerful bond between the cement paste and the aggregate. The rough, angular surface of blasted stone provides a much larger surface area and better mechanical grip for the cement paste to adhere to, resulting in stronger concrete compared to using smooth, rounded gravel.
C. Road Metal
"Road metal" is the term for the crushed stone used in the construction of road pavements, especially in the base and sub-base layers (e.g., Water Bound Macadam or WBM). Just like with railway ballast, the angular, interlocking nature of these stones is crucial for creating a strong, stable foundation that can distribute traffic loads effectively without shifting.
D. All the above
This is the correct answer. The key property of blasted stone—being broken into irregular, angular fragments—is exactly what is required for ballast, concrete aggregate, and road metal. Therefore, it is used for all these purposes.
📊 Summary: Why Angular Stone is Needed
| Application | Required Property | Why Blasted Stone is Ideal |
|---|---|---|
| Railway Ballast | Interlocking & Stability | Angular pieces lock together to resist train loads. |
| Concrete Aggregate | Strong Bond & Grip | Rough, angular surfaces provide excellent adhesion for cement paste. |
| Road Metal | Interlocking & Strength | Forms a strong, stable base layer for roads. |
💡 Study Tips
- Blasting = Broken & Angular: This is the core concept. Blasting doesn't produce neat blocks; it produces shattered, sharp pieces.
- Angular = Interlock: Remember that angular, irregular shapes are excellent at locking together. Smooth, round shapes (like river gravel) easily slide past each other.
- Think "Foundation": All three applications (ballast, aggregate, road metal) are essentially foundation or "filler" materials that need to be strong and stable. Angular stones provide this stability.