What is asphalt binder primarily made up of?

Asphalt binder is primarily made up of bitumen, which is a viscous, black, sticky substance derived from crude oil. This material serves as the glue in asphalt mixtures, binding together aggregates to create a durable and flexible road surface. The properties of bitumen, such as its ability to resist moisture and its strong adhesive qualities, make it an essential component in road construction and maintenance. It also plays a crucial role in providing resistance to deformation and cracking under various loads and temperature changes.

In contrast, water, sand, and clay do not constitute the primary materials in asphalt binder. Water is used in different forms within construction but does not make up asphalt binder itself. Sand and clay can be considered aggregates and may contribute to the overall mix in asphalt concrete but are not the binding agent in the same way that bitumen is. Therefore, bitumen's unique characteristics and its role in enhancing the performance of asphalt mixtures validate its designation as the primary component of asphalt binder.