Adhesion–Friction Coupling in Asphalt Emulsion Surface Treatments: Linking Curing Kinetics, Bond Durability, and Polishing Resistance

Surface treatments including chip seals and high-friction surface treatments (HFST) are vital components of pavement preservation programs used to restore macro/micro-texture friction and address distress. While conventional friction durability studies focus on aggregate mineralogy, this investigation examines the mechanical coupling between binder curing kinetics, micro-scale adhesion, and macro-scale polishing resistance. An experimental matrix evaluating six asphalt emulsion variants (including latex, reactive, and polymer modifications) alongside a thermoset epoxy as a control binder was conducted using two aggregate types (calcined bauxite and rhyolite) across fine and coarse gradations. Materials were evaluated via first-day moisture loss (WL1d), dry and 24 h wet Bitumen Bond Strength (BBS), and British Pendulum Number (BPN) degradation under accelerated polishing. The results reveal a clear relationship between adhesion and friction performance. Ordinary least squares (OLS) modeling reveals that micro-scale bond parameters (BBS) and curing kinetics (WL1d) collectively explain 80.5% of the variance in macro-scale aggregate retention (R2 = 0.805). Furthermore, aggregate retention strongly correlates with early moisture loss (r = 0.872) and wet bond strength (r = 0.6). Advanced elastomeric and polymer modified emulsions (A16 and 1B2Last+16Acro) achieved aggregate retention (R = BPN_after polishing/BPN_before polishing, 86.6% and 85.9%, respectively) and excellent post-polishing friction, performing comparably to the epoxy control (R = 86.5%) while significantly outperforming traditional (CRS-2P) and (CRS-2PSC) systems. The structural impact of binder chemistry was further evaluated through a one-way ANOVA, which confirmed highly significant differences in coarse configurations (p < 0.01). In contrast, the binder effect in fine gradations proved to be highly dependent on aggregate mineralogy; differences were not statistically significant in calcined bauxite (p = 0.270) but reached significance in rhyolite (p = 0.026). Based on these findings, a composite Emulsion Bond Quality Index (EBQI) and a Bond Risk Score (BRS) are introduced. By successfully integrating micro-mechanical bonding, curing kinetics, and polishing resistance, these new metrics establish an objective framework for material selection and process control in pavement preservation practice.