The topmost layer of pavement is known as the wearing course. The wearing course is the layer of pavement that directly comes in contact with vehicles and is designed to withstand the traffic loads and provide a smooth and safe riding surface. It is the final layer of the pavement structure and plays a crucial role in the overall performance and durability of the pavement.

The wearing course is typically made of high-quality materials that are resistant to wear and tear, skid resistance, and weathering. It acts as a protective layer for the underlying layers of the pavement and provides a smooth and comfortable surface for vehicles to travel on. The wearing course also helps in reducing noise and improving visibility during wet conditions.

Key Point: The wearing course is the topmost layer of pavement that directly comes in contact with vehicles and provides a smooth riding surface.

The wearing course is designed to meet specific requirements such as:

1. Skid resistance: The wearing course should have adequate skid resistance to ensure safe vehicle maneuverability, especially during wet conditions. This is achieved by using aggregates with good frictional properties and incorporating additives or surface treatments to improve the skid resistance.

2. Durability: The wearing course should be durable enough to withstand the repetitive traffic loads and resist the effects of weathering and aging. It should be resistant to cracking, rutting, and other distresses that can lead to premature failure of the pavement.

3. Smoothness: The wearing course should provide a smooth and even riding surface to ensure driver comfort and reduce vehicle vibrations. This is achieved by using materials with good shape and gradation, as well as employing proper construction techniques to achieve a uniform thickness and smooth finish.

4. Drainage: The wearing course should have adequate drainage properties to prevent the accumulation of water on the pavement surface. This is important to avoid hydroplaning and maintain skid resistance during wet conditions.

5. Reflectivity: The wearing course can also be designed to have specific reflectivity properties, especially in urban areas or regions with low visibility conditions. This can be achieved by using materials with high reflectance or incorporating reflective additives in the surface treatment.

In conclusion, the wearing course is the topmost layer of pavement that directly comes in contact with vehicles. It is designed to provide a smooth and safe riding surface, withstand traffic loads, and protect the underlying layers of the pavement. It plays a crucial role in the overall performance and durability of the pavement structure.