Multiscale Assessment of Interfacial Adhesion in Granite–Asphalt Systems Enhanced by Layered Double Hydroxides: A Combined Thermodynamic and UV-Aging Study

The objective of this study is to systematically evaluate the reinforcement mechanisms of layered double hydroxides (LDHs) on the aggregate–asphalt interfacial adhesion in granite–asphalt systems under accelerated ultraviolet (UV) aging. The interfacial bonding durability of granite–asphalt composite systems is persistently threatened by hydrothermal stripping and UV weathering. A multiscale experimental framework comprising boiling kinetic tests, photoelectric colorimetry, and surface free energy (SFE) analysis based on the van Oss–Chaudhury–Good theory was executed, complemented by cross-sectional scanning electron microscopy (SEM). Macroscopic results demonstrate that a 3.0 wt.% LDH threshold optimizes the hydrothermal adhesion rating to Level 5. Thermodynamically, introducing 4.5 wt.% LDHs triggers a 176.37% surge in the polar SFE component (γSAB), causing the dry adhesion work (WAS) to peak and the wet stripping work (WALS) to plummet by 45.03%, verifying a significantly compressed driving force for moisture displacement. A reconciliation of these dosage-dependent results establishes 4.5 wt.% as the scientifically optimal formulation for maximizing long-term thermodynamic stability. Microstructural SEM analysis reveals that LDHs transition the terminal UV-degradation behavior from severe, reticulated brittle macro-cracking into highly controlled, damage-tolerant micro-fissuring. These findings provide thermodynamic targets and mechanistic insights that can guide the design of durable, weather-resistant asphalt pavements.