Improvement of compatibility, thermal stability, and rheological properties of composite modified asphalt based on molecular gradient design

The variance in molecular weight stands as the principal reason behind the compromised compatibility within modified asphalt systems. In order to improve the compatibility of modified asphalt, this study integrates the concept of molecular weight gradient design, while considering a balance of performance. Composite modified asphalt samples were prepared using preferred Styrene-Butadiene-Styrene (SBS), Styrene-Butadiene Rubber (SBR), and Butyl Rubber (BR) for comprehensive assessments, including molecular weight distribution, conventional and rheological properties, thermal stability, microstructural morphology, and functional group transformations, and subsequently elucidate the underlying modification mechanisms. The results show that the molecular weight gradient-designed composite modified asphalt exhibits good performance and enhanced compatibility. On the one hand, the styrene and butadiene segments can improve the high and low-temperature performance of the asphalt, respectively. On the other hand, as the molecular weight within the system diminishes, the consistence and hardness of the asphalt decrease, the cross-linking network goes denser, improving compatibility and stability. Moreover, the addition of stabilizer can change the micro-cross-linking network structure and induce functional group transformations of the composite modified asphalt, which conforms to the characteristics of chemical modification.