Multi-scale mechanisms of high-elastic polymer modifiers in enhancing rutting and fatigue resistance of asphalt binders and mixtures

This study systematically investigates three high-elastic polymer modifiers additives (HEA-1, HEA-2, HEA-3) with distinct chemical and physical characteristics through integrated binder- and mixture-level testing, microstructural imaging, and molecular dynamics (MD) simulation. Rheological analyses (DSR, MSCR, LAS) reveal that HEA-1 characterized by high compatibility and molecular diffusion significantly improves fatigue life (up to 11× base asphalt) and moisture resistance (TSR = 80.8%). In contrast, HEA-2 mostly un-melted and acting as granular reinforcement delivers superior rutting resistance (lowest J nr , highest dynamic stability) despite limited molecular integration. Fluorescence microscopy confirms HEA-1 homogeneous dispersion versus HEA-2 phase-separated modifiers, while MD simulations quantify diffusion coefficients (HEA-1: 7.10 × 10 −10 m 2 /s, HEA-2: 4.75 × 10 −10 m 2 /s), correlating strongly with fatigue performance (R 2 > 0.93). Crucially, high-temperature rutting resistance is shown to depend not on binder compatibility but on the physical state of the additive during mixing. These findings establish a dual-pathway framework molecular compatibility governs fatigue and moisture durability, while physical reinforcement dominates rutting resistance. The work provides a mechanistic basis for rational HEAs selection tailored to dominant distress modes, advancing performance-driven sustainable pavement design.