Sand and Gravel Processing Overview
Sand and gravel are essential construction materials used in concrete, asphalt, road base and fill applications. Processing raw sand and gravel requires washing and classification to remove deleterious materials and produce specification-compliant products.
Understanding Sand and Gravel Deposits
Sand and gravel deposits vary significantly in their characteristics:
Alluvial Deposits:
- River-deposited materials
- Generally well-rounded particles
- Variable clay and silt content
- May contain organic materials
Glacial Deposits:
- Variable composition and gradation
- May contain wide range of rock types
- Often requires significant washing
Marine Deposits:
- Salt contamination requires washing
- Generally clean, well-graded
- May need desalination
Feed Preparation and Excavation
Excavation Methods:
- Hydraulic dredging: For below-water-table deposits
- Frontend loaders: For above-water deposits
- Draglines: For large, deep deposits
- Truck and shovel: For pit face excavation
Feed Preparation:
- Screening to remove oversize (boulders, clay balls)
- Slurry pumping for hydraulic transport
- Grit removal before washing
Sand and Gravel Processing Plant Design
Washing Equipment
Log Washers:
- Heavy-duty scrubbing for sticky materials
- Effective at removing clay coatings
- High power consumption
- Best for -50mm material
Scrubbing Trommels:
- Integrated washing and screening
- Lower power than log washers
- Good for moderately dirty material
- Compact design
Attrition Cells:
- For removing soft, friable particles
- Produces clean, sharp sand products
- Often used in combination with other equipment
Classification and Dewatering
Hydrosizers (Teetered Bed Classifiers):
- Separates sand by settling velocity
- Produces multiple sand fractions
- Excellent for concrete sand production
Sand Screws:
- Classifies and dewaters fine sand
- Simple, reliable operation
- Lower cost option
- Typical capacity: 50-500 tph
Dewatering Screens:
- Removes moisture from washed products
- Higher frequency for fine materials
- Often combined with sand screws
Product Specifications
Concrete sand specifications:
- FM (Fineness Modulus): Typically 2.3-3.2
- Clay and silt content: < 3%
- Organic impurities: Low
- Particle shape: Cubical preferred
WSHT provides complete sand and gravel processing plant design, with equipment supply and commissioning support for washing, classification and dewatering systems.
