Microevolution of Polymer–Bitumen Phase Interaction in High-Viscosity Modified Bitumen during the Aging of Reactive Oxygen Species

The objective of this study is to investigate the microevolution of the bitumen microstructure, polymer phase, and polymer–bitumen interaction of high-viscosity modified bitumen (HVMB) in reactive oxygen species (ROS) aging using the Viennese binder aging (VBA) method. First, the VBA system was utilized to age HVMB with different ROS concentrations. Then, an optical inverse bright-field, dark-field, and fluorescence microscope (OIM) was used to observe the bitumen microstructure, its evolution, and polymer structure degradation of HVMB during ROS aging. Afterward, ImageJ software was applied to quantitatively assess the bee structure size characteristics of bitumen and the distribution characteristics of the polymer. Finally, the differences in the distribution features of bee structures in the polymer zone (PZ) and non-polymer zone (NPZ) were counted to understand the polymer–bitumen interaction during ROS aging. The results show that the existence of polymers affects the distribution state of bee structures in bitumen significantly. The area ratio of bee structures and the average area of bee structures in HVMB both progressively rise with an increase in ROS concentration, although both are much less than those in base bitumen (BB). The destruction of the polymer phase starts from the inside of polymers during ROS aging. As the ROS concentration increases, the polymer degrades from the intact network structure to isolated small molecules. Polymer–bitumen interactions are widespread in HVMB. A large number of bitumen bee structures are also present in the PZ of HVMB. Moreover, the bee structures considerably grow in the PZ as opposed to the NPZ during ROS aging. The clarification of these microstructural characteristics lays the foundation for a deeper comprehension of the aging mechanism of HVMB induced by ROS.