Necessity of Directional Cross-Linking of SBS in Asphalt Using Sulfur

For highway maintenance projects, styrene-butadiene-styrene (SBS) modified asphalt (SBSMA) often requires long-term high-temperature storage (typically 10–15 days at temperatures exceeding 150°C), which imposes stringent demands on its thermal storage stability. The limitations of current improvement strategies necessitate the exploration of new approaches to enhance the compatibility of SBS with asphalt. In this study, molecular dynamics simulations were employed for the first time to investigate the influence of SBS cross-linking patterns on compatibility under high-temperature storage conditions. The study emphasizes the critical role of SBS directional cross-linking, with difference in solubility parameters ranging from –12.4% to 33.8% and interaction energy ranging from –10.2% to 23.7%. Second, this study elucidates the compatibility mechanism through a systematic evaluation of nonbonded energy in asphalt, combined with molecular morphological dynamics and the spatial distribution characteristics of directional cross-linked SBS. Self-cross-linked SBS concentrated in the asphaltene region, increasing the agglomeration of SBS, while SBS cross-linked with asphalt localized in the aggregation region of the aromatic, leading to better stretching of SBS within the asphalt and, consequently, improved compatibility. Among these, SBS cross-linked with the aromatic achieves optimal compatibility, making it a key component for future SBS directional cross-linking. Finally, the validity of the simulation indices and results was assessed using Pearson correlation analysis. This study, for the first time to our best knowledge, reveals the compatibility mechanism between SBS and asphalt under multiple cross-linking modes during high-temperature storage, providing a new direction for the directional regulation of SBS cross-linking modes and the improvement of high-temperature storage stability.