Dual-interface cooperative adhesion mechanism of high-asphalt-content emulsified asphalt in recycled asphalt pavement

High-asphalt-content emulsified asphalt (HIACE) shows considerable promise for enhancing reclaimed asphalt pavement (RAP) performance through its unique dual-interface adhesion mechanism. This study synthesised HIACE with 82 % asphalt content using cationic compound emulsifiers. Rejuvenated asphalt (RA) was prepared by incorporating 6 % bio-rejuvenator into laboratory-aged asphalt to investigate the synergistic effects between HIACE, RA, and mineral aggregates at molecular and interfacial levels. Particle size analysis revealed HIACE's distinctive bimodal distribution during storage, with average particle size increasing by 40 % (from 6.02 μm to 8.47 μm) over 22 days, while rheological testing demonstrated that HIACE-RA blends exhibit substantially improved performance compared to RA alone, particularly in high-temperature stability and low-temperature flexibility, with creep stiffness reduced by approximately 50 %. Molecular dynamics simulations revealed the underlying mechanisms: HIACE forms a characteristic "core-shell" microstructure on RA surfaces while displaying substrate-dependent diffusion behaviour—high mobility on RA surfaces (1.38942 Å2/ps) contrasted with strong adhesion to CaCO3 aggregates (0.00235 Å2/ps). Interface energy analysis confirmed HIACE's critical contribution to RAP system performance, providing over 70 % of total interfacial forces through electrostatic interactions with CaCO3 (40.5 %) and van der Waals forces with RA (37.7 %). At the same time, dynamic hydrogen bond networks (averaging 36 bonds) between HIACE and RA facilitated interfacial fusion through three distinct evolutionary stages. These findings provide critical insights into the molecular mechanisms governing HIACE's dual-interface adhesion properties, offering valuable guidance for optimizing recycled asphalt pavement performance and durability.