Comprehensive rheological assessment and optimization of sorbitol-derived bio-polyurethane modified asphalt binders

Abstract

Due to the limitations of passive modifiers, including compatibility and storage stability issues, increasing attention has been directed toward reactive modifiers for asphalt modification. In this study, a bio-based polyurethane (PU) was synthesized using sorbitol as a renewable polyol source and incorporated into a 70/100 penetration-grade asphalt binder at different dosages. The modified binders were evaluated using chemical, conventional, morphological, and rheological analyses, together with response surface methodology (RSM). FTIR analysis confirmed the formation of characteristic polyurethane-related structures. Increasing PU content progressively increased binder consistency and high-temperature resistance; at 7 % PU, penetration decreased by approximately 41 % and the softening point increased by 6.25 °C compared with the neat binder. The viscosity of 7 PU at 135 °C was 1,325 cP, remaining within the acceptable workability range. DSR results showed that the G*/sinδ values of 7 PU were 1.73–2.26 times those of the neat binder between 58 and 76 °C, confirming substantially improved rutting resistance. BBR results further showed an approximately 42 % reduction in creep stiffness for 7 PU at both −12 and −18 °C. Although 7 % PU provided the highest absolute high-temperature performance, RSM and diminishing-return analysis identified approximately 3.26 % PU as a preliminary performance-efficient candidate dosage capable of providing substantial rheological improvement with lower modifier consumption. These findings demonstrate the potential of sorbitol-derived PU for balanced asphalt binder modification while providing a basis for further mixture-level and multi-objective validation.