During which stage does the most oxidation occur in an asphalt binder?

The stage during which the most oxidation occurs in an asphalt binder is when the hot mix asphalt (HMA) is being mixed, placed, and compacted. This is a critical time for the binder, as high temperatures and exposure to air can significantly elevate the rate of oxidation.

When asphalt binder is heated during mixing, it is often in a state that allows for chemical reactions such as oxidation to take place more readily. The presence of oxygen at elevated temperatures promotes oxidation, leading to increased viscosity and hardening of the binder. This brings about changes that can affect the overall quality and performance of the asphalt mix, including its durability and resistance to distresses such as cracking.

Furthermore, during the placement and compaction phases, the binder remains exposed to atmospheric conditions, which can contribute additional exposure to oxygen. The compaction process also generates shear forces, which can enhance the interaction between the binder and air, thus further increasing oxidation.

Understanding that this oxidation during the mixing, placing, and compacting stages is crucial for quality control and achieving the desired performance characteristics of the finished pavement.