Research on key factors influencing viscosity growth of thermosetting polyurethane modified asphalt

Abstract As a typical thermosetting material, viscosity is critical in the compaction process of thermosetting polyurethane (PU)-modified asphalt (TPUA) pavement systems. However, limited research on the key factors governing TPUA viscosity has hindered the precise control of its allowable construction time. In this study, a TPUA binder was synthesized using modified hexamethylene diisocyanate (HDI) as the main agent, polytetramethylene ether glycol (PTMG) as the soft segment, and 1,4-butanediol (BDO) as the chain extender. The effects of external factors (preparation methods, curing temperature, PU content) and internal factors (soft segment molecular weight, hard segment content, reactive group ratio) on the viscosity growth of modified asphalt were systematically investigated. The results showed that Both two-component and three-component preparation methods exhibited negligible differences in viscosity growth and allowable construction time of TPUA binders. Higher curing temperatures accelerated viscosity growth rates, significantly shortening the allowable construction window. When the curing temperature increased by 5 °C, the allowable construction time decreased by 6 to 10 min. Moreover, A viscosity-temperature evolution model was proposed, effectively simulating the initial viscosity changes of TPUA binder. Increased soft segment molecular weight, hard segment content, and reactive group ratio accelerated viscosity growth and reduced allowable construction time. Allowable construction time correlated positively with PU content, with a recommended minimum PU dosage of 30 wt% to ensure workability. Comprehensive analysis identified hard segment content, PU dosage, and curing temperature as the most critical parameters governing viscosity growth and allowable construction time. These results provide critical insights for optimizing TPUA formulations and curing protocols to balance processability and performance in pavement engineering applications.