Experimental analysis and molecular dynamics simulation of anti-aging performance of weather-resistant polyurethane-modified asphalt

To expand the application of polyurethane-modified asphalt (PUA) materials in special asphalt pavements, a new weather-resistant PUA containing dynamic covalent disulfide (S-S) bonds was developed. To enhance the mechanical properties of asphalt pavement materials, while extending its service life simultaneously, the durability of this novel PUA was thoroughly investigated in this study. The prepared PUA was subjected to long-term thermo-oxidative or ultraviolet (UV) aging. Changes in rheological properties of PUA before and after aging were evaluated by a dynamic shear rheometer. The modification mechanism of S-S bonds during the aging process of PUA was analyzed by a series of microscopic experiments, and the effects of aging on the motion properties of PUA components were characterized by molecular dynamics (MD) simulation. The aging indexes derived from laboratory tests illustrated that UV aging had a more detrimental effect on the rheological properties and fatigue resistance of PUA than thermo-oxidative aging, which increased the surface roughness and fold fluctuation of PUA. In contrast, the introduction of S-S bonds facilitated the intertwining of the PU chains and formed a reversible network structure with asphalt. Under the moderate temperature stimulation, S-S bonds accelerated the dynamic exchange process by absorbing part of the UV light, which promoted the recovery of the network structure formed by PU molecules on the asphalt surface, thus enhancing its durability. The results of MD simulation indicated that the asphaltene molecules in PUA aggregated and arranged in order under the promotion of S-S bonds, resulting in higher mechanical modulus and structural stability after aging. The antiaging behavior of weather-resistant PUA could be more comprehensively characterized by combining macroscopic, microscopic and molecular scales, which provided a basis for its long-term use as a pavement material.