Crushed Stone (Mechanically Produced): Overview and Process
Crushed stone is a construction aggregate produced by mechanically breaking down larger rocks into smaller, angular fragments. The mechanical production process ensures uniformity in size and shape, making it suitable for various applications like concrete, road base, drainage, and landscaping.
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Mechanical Production Process:
1. Blasting & Quarrying:
– Large rocks are extracted from quarries using controlled explosions or heavy machinery (e.g., excavators).
– Raw material (limestone, granite, trap rock, etc.) is selected based on intended use.
2. Primary Crushing:
– Rocks are fed into a jaw crusher or gyratory crusher to reduce them to coarse fragments (~6–12 inches).
3. Secondary Crushing:
– Smaller crushers (e.g., cone crushers or impact crushers) further break down the material into finer grades (e.g., 1–3 inches).
4. Screening:
– Vibrating screens separate crushed stone into specific sizes (e.g., #57, #3, or #411 stone).
– Oversized material is recycled back into the crusher.
5. Tertiary Crushing (Optional):
– For very fine aggregates (e.g., manufactured sand), vertical shaft impactors (VSIs) may be used.
6. Washing & Sorting (Optional):
– Some operations use log washers to remove clay or dust for cleaner stone.
Key Properties of Mechanically Crushed Stone:
– Angularity: Mechanically crushed edges improve interlocking for stability.
– Gradation: Sized for specific uses (e.g., base layers require well-graded stone).
– Durability: High compressive strength depending on parent rock type.
Common Uses:
– Road construction (sub-base or asphalt mix)
– Concrete aggregate
– Drainage systems (French drains)
– Railroad ballast
– Landscaping and erosion control
Advantages of Mechanical Production:
✔ Consistent size and shape for engineering specifications.
✔ Scalable output to meet demand.
✔ Recyclability of waste rock back into the process.
Would you like details on specific standards (e.g., ASTM or AASHTO gradations) or equipment types?
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