Road construction utilizes varying stone sizes depending on the layer.
Sub-base layer (40 – 80 mm): Larger aggregates (like #1 or #3 grade) provide a robust, structural foundation and reliable sub-surface drainage.
Base Course (20 – 40 mm): This layer distributes traffic loads. Commonly, a graded mix like #411 (Crusher Run) is used, which combines coarse stones and fine dust for superior interlocking and compaction.
Surface / Wearing Course (5 – 20 mm): Finer aggregates (such as #57 or #67 stone, roughly 10 – 20 mm) are chosen. These tightly lock together to create a smooth, dense, water-resistant driving surface.
Bedding/Dust (Under 5 mm): Crusher dust or screenings are used as a final filler and binder.
Crusher Selection Plan (Based on Material Hardness)
High-Hardness Materials (granite, basalt, river pebbles)
Configuration: Jaw crusher (primary crushing) + Cone crusher (secondary and fine crushing) + Impact crusher (shaping / sand making, optional).
Reason: Cone crushers have strong wear resistance and low operating costs, making them suitable for rocks with high compressive strength. Impact crushers consume too many wear parts on such materials.
Medium-to-Low Hardness Materials (limestone, bluestone, shale)
Configuration: Jaw crusher (primary crushing) + Impact crusher (secondary and fine crushing) – or a heavy hammer crusher (one-stage forming).
Reason: Impact crushers produce a good particle shape (more cubical particles, fewer flaky and elongated ones), and their operating cost for medium-hard materials is lower than that of cone crushers. Hammer crushers are suitable for small-scale production lines that aim for a simplified process.
Special Condition (space-constrained sites, construction waste recycling)
Configuration: Track-mounted or tyre-mounted mobile crushing plants (which can flexibly combine the above main crushers).
Reason: They require no foundation piles and can be driven directly to the job site, making them ideal for scattered operations along highway routes.
Key Selection Recommendations
Primary crushing stage: Regardless of the material, a jaw crusher is the first choice for processing large blocks of raw stone.
Particle shape requirements: High-grade highway asphalt surfaces demand very high aggregate shape quality. Therefore, an impact crusher or vertical shaft impact crusher must be added in the secondary/fine crushing stage for shaping, in order to reduce the content of flaky and elongated particles.
Process combination: A standard production line typically follows: feeder → jaw crusher → screening → cone/impact crusher → re-screening → finished products. A closed-circuit loop ensures precise gradation control.
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