Optimization design and curing behaviors of polyurethane (PU) modified asphalt from the perspective of cohesion-adhesion variations

Interface properties of asphalt and aggregate intimately affect the service-performance and durability of asphalt pavement . The research aimed to explore the cohesion-adhesion characteristics of polyurethane (PU) modified asphalt, and thus optimizing its constituent proportion and understanding its curing behaviors. To this end, several proportion schemes of PU modified asphalt were first designed with response surface methodology (RSM), and the corresponding asphalt binders were prepared and their cohesion-adhesion features were characterized based on contact angle test and thermodynamic theory. On this basis, the effects of composition ratio and its interactions on the cohesion-adhesion features were analyzed and the optimal composition ratio was determined. Lastly, the adhesion features of PU modified asphalt during its curing period were measured using pull-out test and atomic force microscopy (AFM), and thus the curing behaviors were expounded. The results showed that the composition-associated factors had interactive impacts on the cohesion and adhesion of PU modified asphalt, wherein the influence of PU prepolymer on the adhesion was more significant as the curing agent was incorporated at the high ratio. Further, the increase of compatibilizer and diluent adversely affected the cohesion-adhesion capacity of PU modified asphalt, and for obtaining the favorable cohesion-adhesion competence, the optimal constituent proportion was determined as PU prepolymer: curing agent: compatibilizer: diluent = 14: 1.80: 1.88: 3.12. During the curing process, the adhesion performance and microscopic phase structure of PU modified asphalt exhibited the character of an initially visible ascending variation followed by a tendency to stabilize, and the eventual adhesion properties were not related to the solidification temperature set in the research. The research is of great significance for guiding the development of PU modified asphalt with satisfactory interfacial properties and understanding its curing process. • Effects of material composition of PU modified asphalt on its interfacial properties were explored. • Variations of adhesive features of PU modified asphalt during its curing stage were investigated. • PU prepolymer and curing agent chiefly affected the cohesion at their both lower and higher ranges. • Final adhesion properties of PU modified asphalt were independent of curing temperature.