1. Surface Layer (Wearing Course)
• Description: The topmost layer of the pavement, directly exposed to traffic.
• Function: Provides a smooth, skid-resistant surface for vehicles, protects underlying layers from weather and traffic, and ensures water runoff.
• Materials: Asphalt concrete or Portland cement concrete (PCC), often with additives for improved durability and resistance.
2. Binder Course
• Description: A layer beneath the surface that distributes traffic loads to the base and sub-base layers.
• Function: Reduces the load transmitted to the lower layers, providing additional support to the surface layer.
• Materials: Often a bituminous mix (in asphalt pavements) with coarser aggregates for stability.
3. Base Course
• Description: A thick layer that lies beneath the binder course (or surface layer, in some designs).
• Function: Distributes load pressures evenly to prevent deformation and adds structural strength to the pavement.
• Materials: Crushed stone, crushed gravel, or stabilized materials like bitumen or cement-treated bases.
4. Sub-base Layer
• Description: The layer beneath the base course, often thicker in flexible pavements.
• Function: Provides additional load distribution, aids drainage, and prevents fine materials from the subgrade from moving into upper layers.
• Materials: Coarse aggregates, recycled materials, or treated soils.
5. Subgrade
• Description: The natural soil layer or prepared soil that serves as the foundation for the pavement.
• Function: Supports the entire pavement structure, distributes traffic loads to the ground, and impacts pavement longevity.
• Materials: Compacted native soil or imported fill material; often stabilized with additives to increase strength.
Each layer plays a critical role in ensuring the pavement can withstand heavy loads, resist wear, and maintain a smooth driving surface over time. The design and thickness of each layer depend on factors like expected traffic volume, environmental conditions, and soil characteristics.
