Effects of Warm-Mix Agents on the Thermal Stability of SBS-Modified Asphalt

To evaluate the susceptibility of styrene–butadiene–styrene (SBS)-modified asphalt to modifier segregation during high-temperature storage, this study examined its segregation behavior and microstructural evolution under storage conditions ranging from 70 to 163 °C over durations of 48–144 h, with varying warm-mix agent dosages (0%, 3%, 4%, and 5%). The investigation was conducted using softening point measurements, dynamic shear rheometry, infrared spectroscopy, and optical microscopy. The results indicated that the incorporation of the warm-mix agent significantly reduced the difference in softening point, diminished the discrepancies in complex modulus and phase angle between the upper and lower layers, and inhibited SBS aggregation and phase separation. When the warm-mix agent content reached 5%, the softening point difference in the modified asphalt at 163 °C and 48 h decreased from 14.4 °C to 1.6 °C, essentially eliminating segregation. Infrared spectroscopy confirmed that the warm-mix agent did not induce chemical bond changes but improved the compatibility between the SBS modifier and the base asphalt. Microscopic observation further verified that the warm-mix agent facilitated a uniform dispersion of SBS modifier particles, forming a stable microphase structure. The research findings provide valuable insights for improving the storage stability and engineering performance of SBS-modified asphalt.