Aging of steel slag-modified styrene-butadiene-styrene/crumb rubber asphalt mastic: Mechanism of steel slag on the evolution of asphalt microstructure

The widespread use of steel slag in bitumen mixtures necessitates a deeper investigation into its impact on asphalt aging. This study explores the influence mechanism of steel slag powder (SSP) on the aging behavior of styrene-butadiene-styrene/crumb rubber modified bitumen mastic. Through various characterization techniques, including rheological testing, relaxation characteristic temperature analysis, UV–visible spectroscopy, fluorescence microscopy (FM), and Fourier-transform infrared spectroscopy (FTIR), the study reveals the effects of SSP on short-term, UV, and long-term aging of asphalt mastic. The research shows that after aging, the elastic response and the half-peak width of the relaxation characteristic temperature of asphalt mastic significantly increase, while its temperature sensitivity and viscous dissipation capacity are reduced, indicating that SSP has a negative effect on asphalt aging. SSP increases the absorbance in UV–visible light spectra. FTIR analysis indicates the oxidation of asphalt light components (increase in the characteristic peak of C[dbnd]O bonds) and the breakage of polymer chains (disappearance of the characteristic peak of C[dbnd]C bonds in SBS). FM analysis shows that the cross-linked network structure disappears after UV aging and long-term aging, which suggests the possible role of active components in SSP (such as Fe₂O₃ and TiO₂) in promoting the UV aging of asphalt mastic. Moreover, the high specific gravity of SSP exacerbates asphalt phase separation and promotes oxygen diffusion, significantly weakening the anti-aging advantages of the modifier and accelerating the aging of bitumen mastic. This study provides important theoretical support for the durability design and synergistic optimization of anti-aging performance of steel slag bitumen mixtures.