What type of aggregate is specifically used in friction course mixes?

The use of polish-resistant aggregate in friction course mixes is critical due to its enhanced durability and performance in providing adequate skid resistance. Friction courses are asphalt layers specifically designed to improve the surface texture of the pavement, which helps in maintaining traction between vehicle tires and the roadway, especially in wet conditions.

Polish-resistant aggregates are characterized by their ability to retain their texture and surface roughness even under high traffic volumes, where other types of aggregates may become smooth and polished. This trait is essential for ensuring safety and preventing slip accidents, particularly in areas with high-speed traffic or challenging weather conditions.

While other aggregates like granite aggregate can provide strength and stability, and recycled aggregate can be a sustainable option, they may not possess the same level of resistance to polishing as specifically labeled polish-resistant aggregates. Sand aggregates, on the other hand, typically do not offer the structural integrity or the coarse texture needed for friction courses. Thus, the correct choice focuses on materials that ensure optimal performance of the pavement surface.