Molecular mechanisms governing the deterioration of cracking resistance in asphalt induced by aging

Understanding the molecular mechanisms by which asphalt pavement aging diminishes its cracking resistance is essential for guiding rejuvenator design. This study investigated Donghai asphalt (60/80 penetration) across four states: Unaged, short-term aged, and long-term aged (20 h and 40 h). Microstructural characteristics were characterized using SARA (saturates, aromatics, resins, and asphaltenes) fraction analysis, Fourier transform infrared spectroscopy (FTIR), and elemental analysis, while macroscopic fatigue cracking resistance was evaluated through linear amplitude sweep (LAS) tests. Molecular models representing different aging states were constructed based on the SARA fraction proportion, followed by molecular dynamics (MD) simulations under single tensile and cyclic fatigue loading. Results indicate that the SARA fraction exerts a more significant influence on fatigue cracking resistance than elemental composition. Under single tension, ultimate tensile strength (UTS) increased by 75.91%–98.89% with rising loading rates, which was accompanied by increased fracture energy. However, temperature elevation from 253 K to 323 K reduced both UTS and modulus. Progressive aging increased UTS but decreased fracture energy, suggesting enhanced resistance to single-event cracking yet compromised resistance to fatigue cracking. Under cyclic loading, UTS and fracture energy progressively decreased with increasing cycles, with more pronounced degradation in highly aged asphalt. Mechanistically, aging-induced polar functional groups promoted molecular aggregation and reduced self-diffusion coefficients, thereby restricting stress relaxation and self-healing capacity, which governs fatigue deterioration.