Degradation mechanisms of salt-storage asphalt pavements: molecular dynamics insights into salt-water coupling effects on asphalt and aggregate interface

Salt-induced asphalt interface failure severely limits the service life of salt-storage snow-melting asphalt pavements. Employing eco-friendly sodium formate as organic salts representative, this study employs interfacial strength tests and molecular modeling to reveal salt interactions with asphalt and asphalt-aggregate interfaces. On this basis, the degradation pathways of interfacial interaction under salt-water coupling are further revealed by introducing water molecular to construct the ternary system coupled (asphalt/water/aggregate) interface molecular models. Key findings reveal that sodium formate storage filler incorporation significantly reduces asphalt components diffusivity by 34.5%–41.9% within the asphalt model. This inhibition impedes molecular conformational adjustment and accelerates asphalt damage accumulation. Concurrently, sodium formate molecule degrades the asphalt/aggregate interfacial properties through the dual mechanism: Salt enhances asphalt molecular surface mobility, while simultaneously promoting interfacial salt aggregation. The dual synergistic effect would reduce the molecular folding level and interfacial electrostatic energy, which leads to the adhesion properties showing high salt sensitivity. Comparatively, it was found that silicon dioxide minerals showed superior interfacial stability than calcium carbonate minerals in salt-eroding environments. Under saline-water coupling conditions, progressive salt precipitation from salt-storage asphalt induces a sustained increase in salinity concentration of water layer. This phenomenon can cause the reduction in the water mobility by about 30% and an increase in the interlayer retention effect, and thereby forming a barrier that further weakens interface interaction energy. These results provide theoretical foundation for optimizing salt-storage asphalt pavement design and enhancing the sustainability of asphalt pavements.