Optimization of emulsified asphalt/aggregate interfacial adhesion driven by asphalt aromatic carbon ratio: Acid-base collaboration mechanism

Emulsified asphalt is a critical component of low-temperature pavement materials and plays a pivotal role in determining the durability of asphalt mixtures through its demulsification and adhesion characteristics. This study investigates the synergistic effects of asphalt aromatic carbon ratio, emulsifier types (SDBS/STAC), and oxide types (CaCO₃/SiO₂) on emulsified asphalt performance through experiments and molecular simulations. Experiment results demonstrate that higher aromatic carbon content proportionally extends demulsification time. An “acid-base collaboration” mechanism governs interfacial energy: on basic oxides (CaCO₃), interfacial energy inversely correlates with aromatic carbon ratio; on acidic oxides (SiO₂), SDBS-emulsified systems show positive correlation while STAC-emulsified systems show negative correlation. High aromatic carbon asphalt forms ordered bimodal interfaces despite loose molecular packing, while low aromatic carbon asphalt exhibits disordered interfaces with more compact aggregation. On bare oxide surfaces, asphalt molecular diffusion increases by 25.99 % with rising aromatic carbon ratio, but decreases by 32.30 % on acidic surfaces. Based on these findings, low aromatic carbon asphalt with STAC emulsifier is recommended for interface optimization for basic aggregates. In contrast, acidic aggregates benefit from either high aromatic carbon asphalt with SDBS or low aromatic carbon asphalt with STAC. This “aromatic carbon ratio-emulsifier-oxide type” regulatory mechanism provides a theoretical foundation for controlling emulsified asphalt breaking time and enhancing adhesion performance, advancing energy-efficient pavement technology.