Which material is primarily used as a binder in asphalt?

The primary material used as a binder in asphalt is asphalt binder. This binder is a complex mixture, primarily composed of bitumen, which serves to hold the aggregate particles together in asphalt concrete. The quality and properties of asphalt binder greatly influence the performance and durability of the asphalt pavement, making it essential in the construction and maintenance of roads.

The other materials listed have different roles or applications. Concrete is a completely different construction material altogether and does not serve as a binder in asphalt. Coal tar, while it can be used in some specific applications, is not the primary binder in asphalt mixes and is less common due to environmental concerns. Gypsum is primarily used as a material in the production of drywall and does not have any significant application in asphalt mixtures. Thus, asphalt binder stands out as the most accurate and relevant answer regarding the primary binder used in asphalt.