In road construction, sand and gravel serve as the main aggregate materials. Their quality directly affects the strength, stability, and durability of the pavement. To ensure engineering quality, sand and gravel must meet several key technical requirements and be produced through a standardized process.
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I. Technical Requirements for Road Aggregates
1. Particle Size and Gradation
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Coarse aggregate (crushed stone): Typically ranges from 5 to 31.5 mm, with common specifications including 5–10 mm, 10–20 mm, and 16–31.5 mm.
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Fine aggregate (manufactured sand): Ranges from 0.075 to 4.75 mm.
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Well-graded: Ensures the mixture is dense and stable, reducing the risk of settlement or cracking.
2. Clay and Fines Content
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Manufactured sand: Clay content ≤ 3%, stone powder content ≤ 10%.
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Crushed stone: Clay content ≤ 1%.
Excessive clay content can affect bonding with cement or asphalt, reducing the structural strength of the pavement.
3. Strength and Crushing Value
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Crushing value: For expressways and highways, it should be ≤ 12%; for general roads, ≤ 15%.
Hard rocks such as granite, basalt, and diabase are recommended as raw materials due to their high strength.
4. Flaky and Elongated Particles
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Should be controlled within 15%, with stricter limits for higher-grade roads.
Excessive flaky particles reduce the packing density and structural stability of the mixture.
5. Cleanliness and Impurities
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Sand and gravel should be free from organic matter, mud, roots, and other impurities.
Pre-use processing such as dust removal and screening should be done to ensure cleanliness.
6. Other Properties
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Abrasion resistance: Generally required to be ≤30%.
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Water absorption: Should not be too high to avoid affecting the water-cement ratio in construction.
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Weather resistance: Aggregates should maintain strength under sunlight, rain, and other environmental conditions.
II. Production Process of Sand for Road Construction
To ensure aggregate quality, a scientific and reasonable sand-making process should be followed, including the following steps:
1. Raw Material Selection
Choose hard and durable stones such as granite, basalt, or limestone as raw materials.
2. Primary Crushing
Use a jaw crusher to break large stones into smaller sizes for further processing.
3. Secondary and Tertiary Crushing
Use cone crushers or impact crushers to further reduce the material size and improve particle shape.
4. Sand Making and Shaping
Use a sand-making machine (e.g., VSI impact crusher) to produce manufactured sand with uniform size and proper gradation.
5. Screening and Classification
Use vibrating screens to divide the finished material into different size ranges, ensuring they meet road engineering design standards.
6. Washing and Cleaning
Use sand washing machines to remove stone powder, mud, and other impurities, improving cleanliness and performance.
7. Storage and Transportation
Finished aggregates should be stockpiled, sealed, or transported by size category to avoid contamination or mixing.
Conclusion
High-quality sand and gravel are the foundation of road engineering. By following a standardized sand production process and strict quality control, it is possible to produce high-performance aggregates that meet road construction standards and provide strong support for infrastructure development.
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