The distinctive microstructures in bitumen and their indication of bitumen’s phase stability

Bitumen, similar to some amorphous polymeric systems, display diverse microstructures that are related to bitumen’s bulk physical and rheological properties; yet the chemical-microstructural-mechanical relationships for bitumen have been very challenging to establish due to bitumen’s complicated molecular interactions. To tackle this challenge, we chose two pristine bitumen (i.e., ABD and AAD), separated them into their asphaltene and maltene fractions, and prepared derivative bitumen by remixing their corresponding asphaltenes and maltenes at different ratios. We studied the microstructures of the two pristine bitumen and their derivatives using atomic force microscopy (AFM), and their phase stability using differential scanning calorimetry and their rheology using dynamic shear rheometry. Our results suggest that AAD-based derivatives had phase separation; in contrast, ABD-based samples were phase stable. The difference in phase stability between the two groups of bitumen is largely relevant to the aggregation behavior of their respective asphaltene fraction that was measured via NMR.