Phase diagram analysis of SBS modified bitumen using rheological and optical techniques

A quantitative investigation of phase diagrams in polymer-modified bitumen is essential for understanding its stability, yet this area remains underexplored. This study focuses on styrene–butadiene–styrene (SBS) copolymer modified bitumen as the target material. Rheological methods were utilized to determine the binodal and spinodal lines, resulting in thermodynamic phase diagrams for varying SBS contents that exhibit characteristics of Lower Critical Solution Temperature (LCST). Additionally, optical microscopy was employed to assess the phase separation temperature through the intensity-temperature variation curve. Taking the bitumen/SBS (100/4) combination as an example, the isothermal evolution of phase separation structures at two different temperatures was analyzed. The results indicate that SBS-modified bitumen forms an SBS-rich network structure driven by viscoelastic phase separation, illustrating the dynamic asymmetry between bitumen and SBS. This research enhances our understanding of the phase behavior and dynamics of SBS-modified bitumen, offering valuable insights for the stability study of polymer-modified bitumen.