Optical characterization of temperature- and composition-dependent microstructure in asphalt binders

Area of Science:

• Materials Science
• Chemical Engineering
• Physical Chemistry

Background:

• Asphalt binder microstructure significantly influences its performance and aging characteristics.
• Understanding the dynamic behavior of these microstructures under thermal stress is crucial for predicting asphalt durability.

Purpose of the Study:

• To characterize asphalt binder microstructure using noncontact optical methods.
• To correlate microstructural changes with bulk rheological properties over a wide temperature range (15°C to 85°C).

Main Methods:

• Noncontact optical microscopy and optical scattering techniques were employed.
• Measurements were benchmarked against rheometric measurements of the complex shear modulus |G*(T)|.
• Two compositionally different asphalt binders were analyzed across thermal cycles.

Main Results:

• Elongated 'bees' microstructures were resolved optically at the surface, disappearing after thermal cycling.
• Smaller, bulk-residing 'ants' microstructures persisted through thermal cycles and scattered light strongly.
• Optical scattering from 'ants' exhibited hysteresis with temperature, mirroring rheometric |G*(T)| hysteresis, suggesting microstructural volume fraction changes.

Conclusions:

• Optical methods can effectively characterize asphalt binder microstructures and their thermal responses.
• The observed hysteresis in optical scattering and rheology indicates thermally driven microstructural changes impact bulk binder properties.
• These findings provide a new optical approach to assess asphalt binder behavior and potential for performance prediction.