Asphalt binder increasing in stiffness over time when exposed to air is an example of what property?

• A. Flexibility
• B. Durability
• C. Viscosity
• D. Oxidation

Answer: (D)

The phenomenon of asphalt binder increasing in stiffness over time when exposed to air is primarily attributed to oxidation. When asphalt is exposed to oxygen in the atmosphere, chemical reactions occur that lead to the formation of oxidized compounds. This process increases the viscosity and stiffness of the binder, affecting its performance in various temperature and loading conditions. Understanding oxidation is crucial for asphalt paving because it directly influences the longevity and durability of the asphalt pavement. Over time, the increased stiffness can lead to issues like cracking and reduced flexibility, which are undesirable in a paving material. Thus, oxidation is the correct answer as it specifically describes the chemical changes that result in the observed increase in stiffness due to air exposure.