Bitumen’s microstructures are correlated with its bulk thermal and rheological properties

Abstract

Understanding of how the chemistry of asphalt binders (i.e., bitumens) affects their bulk properties is critical for development of structure-related mechanical models and performance-based specifications for asphalt binders and asphalt-related applications. However, establishing the chemical-mechanical relationships that govern asphalt binders’ properties remains a challenge due to binders’ complex chemical makeup and the intriguing molecular interactions among binders’ various chemical constituents. Here, we investigate the effect of chemical composition on binders’ microstructure, thermal, and rheological behavior. Two virgin binders (i.e., ABD and AAD) from different crude oil origins were chosen and a series of derivative binders was made by remixing different weight ratios of the asphaltenes and the maltenes obtained from the two source binders. Thermal and rheological properties of all binders were measured using modulated differential scanning calorimetry and dynamic shear rheometry, respectively. Binders’ microscopic characteristics (e.g., microstructures and their contrast in phase images) were evaluated using atomic force microscopy. Our results show that bitumens’ characteristic microstructures, as a result of the complex molecular interactions among their various chemical components, are correlated with their bulk thermal and mechanical properties. Notably, the asphaltene/maltene ratio alone cannot predict a bitumen’s bulk properties. Instead, a bitumen’s distinctive microstructures along with its colloidal index, provide meaningful insights into effect of chemical composition on glass transition, phase stability, and rheological properties of the bitumen.