Pure and Mg/Al-Doped ZnO Nanoparticle-Modified Asphalts for Improved Anti-UV Aging Performance

Due to the strong absorption of ultraviolet (UV) light, nanoparticles such as zinc oxide (ZnO) can effectively improve the anti-UV aging performance of asphalt. However, the underlying mechanism of aging behaviors in nanoparticle-modified asphalt remains unclear. In this study, we experimentally investigated the anti-UV aging performances of asphalts modified by pure and Mg/Al-doped ZnO (Zn 0.97 Mg 0.03 O; Zn 0.97 Al 0.03 O). Furthermore, the underlying mechanism is revealed in detail by density functional theory (DFT) and molecular dynamics simulations. The results show that ZnO nanoparticles improve the anti-UV aging performances of asphalt, while this improvement is further enhanced by Mg/Al doping. Besides UV absorption of nanoparticles, electron transfer from nanoparticles to asphalt molecules, as revealed by DFT, is found to play a crucial role. This electron transfer can lower the reaction energy barrier for dehydrogenation reactions, facilitating oxidation. Meanwhile, it also can disperse the aged asphaltene by increasing the interaction energy, thereby further improving the anti-UV aging performance. Compared to pure ZnO, Mg/Al doping reduces the electron transfer to the asphaltene, which leads to reduced asphalt oxidation and thus better anti-UV aging improvements. The underlying mechanism established in the present work is useful to understand and protect UV aging of asphalt.