Enhancing the Comprehensive Performance and Interfacial Adhesion of Emulsified Asphalt Using an Epoxy-Functionalized Waterborne Polyurethane

To enhance the comprehensive performance and interfacial adhesion of conventional emulsified asphalt, an epoxy-functionalized waterborne polyurethane modified emulsified asphalt (EFPU-MEA) was developed using an epoxy-functionalized waterborne polyurethane (EFPU) emulsion and an isocyanate curing agent. Experimental evaluations show that the EFPU-MEA achieves a tensile strength of 1.11 ± 0.05 MPa and an elongation at break of 782.5 ± 45%, demonstrating a well-balanced flexibility and deformation resistance. The interfacial bond between EFPU-MEA and aggregates exhibited robust durability under various stressors, including thermal fluctuations, low-temperature cracking, chemical corrosion, and moisture damage. Quantitative “sandwich” pull-out and shear tests determined the optimal modifier content and spraying quantity to be 15–20% and 1.0 kg/m2, respectively. Under these conditions, the system maintained high bond strength following severe freeze–thaw cycles and chemical erosion. Mechanistically, fluorescence microscopy (FM) confirmed a uniform dispersion of EFPU within the asphalt matrix, providing effective physical reinforcement. Furthermore, surface free energy (SFE) analysis and Fourier Transform Infrared (FTIR) spectroscopy revealed that internal chemical crosslinking restructures the binder’s surface thermodynamics, significantly increasing the surface polarity and adhesion work. Finally, road performance tests—including marshall stability, wet track abrasion, and rutting resistance—verified the engineering durability of the EFPU-MEA mixture. These findings provide a theoretical and practical basis for the use of EFPU-MEA in extending the service life of high-grade highway pavements.