What impact does air exposure have on asphalt binder over time?

Air exposure has a significant impact on asphalt binder over time, leading to degradation and stiffening. When asphalt binder is exposed to air, it undergoes a process known as oxidation. This process involves the chemical reaction between the asphalt components and oxygen, resulting in the formation of new compounds that alter the physical properties of the binder.

As oxidation progresses, the binder's viscosity increases, making it stiffer and reducing its flexibility. This change is critical because it can greatly affect the performance of the asphalt mixture, leading to problems such as cracking and reduced durability. Understanding the implications of air exposure is essential for maintaining the quality of asphalt mixtures and ensuring they can withstand environmental stresses over their service life.

Consequently, the impact of air exposure on asphalt binder is primarily characterized by degradation and stiffening, aligning with the choice that highlights these effects.