Explain the concept of "reaction of the asphalt binder with oxygen."

The reaction of asphalt binder with oxygen primarily results in oxidation, which is a chemical process that occurs when the asphalt is exposed to air over time. This oxidation leads to changes in the properties of the asphalt, specifically causing it to harden and become more brittle. The process involves the asphalt binder reacting with oxygen molecules, which modifies its structure and reduces its workability and flexibility.

As the binder ages, oxidation contributes to the formation of new compounds within the asphalt, which can impede its ability to effectively bond with aggregates and perform under varying temperature conditions. This hardening effect is often detrimental to the long-term performance of asphalt pavements, as it can lead to cracking and other forms of distress in the surface.

While factors like the adhesive properties of asphalt can be influenced by various conditions, the predominant outcome of the interaction between asphalt binder and oxygen is indeed the hardening effect due to oxidation. This understanding is crucial for managing the performance and longevity of asphalt mixtures in road construction and maintenance.