Multi-scale characterization and statistical analysis on aging behaviors of SBS modified asphalt exposed to plateau environments: Morphology, rheology and mechanism

The extreme climatic conditions on the Qinghai-Tibet Plateau (QTP), characterized by intense ultraviolet (UV) radiation and drastic temperature fluctuations, exert severe aging threats to styrene-butadiene-styrene modified asphalt (SBSMA). To investigate the aging behavior and performance evolution of SBSMA under such a complex environment, this study developed a coupled plateau aging (CPA) protocol based on field meteorological parameters, with individual UV aging (UVA) serving as the control. On this basis, the multi-scale morphological characteristics of the aged SBSMA were characterized via surface observation, fluorescence microscopy (FM), and atomic force microscopy (AFM). The rheological properties of SBSMA over a wide temperature range were evaluated through temperature sweep (TS), multiple stress creep recovery (MSCR), linear amplitude sweep (LAS), and bending beam rheometer (BBR) tests. The evolution in the chemical compositions of the aged binder were analyzed using Fourier transform infrared spectroscopy (FT-IR), gel permeation chromatography (GPC), and thin-layer chromatography with flame ionization detection (TLC-FID). Furthermore, Hierarchical cluster analysis (HCA) and Spearman rank correlation analysis (SRCA) were integrated to reveal the correlations between microscopic mechanism indicators and macroscopic performance parameters, clarifying the aging patterns of SBSMA under UVA and CPA conditions. The results indicated that: (1) Under long-term CPA, severe cracks developed on the surface of the aged SBSMA, accompanied by a significant reduction in the fluorescent area and a substantial increase in micro roughness. (2) The overall performance of the SBSMA continuously degraded during the aging duration, and the deterioration effects under CPA were more pronounced than those under UVA. (3) Under both aging conditions, the SBSMA aging process followed a two-stage mechanism, shifting from being dominated by SBS degradation to being dominated by asphalt oxidation, with the transition occurring earlier under CPA. (4) When exposed to long-term aging, CPA resulted in a lower oxidation degree of the matrix asphalt, while inducing earlier and more thorough SBS degradation. (5) The microscopic mechanism indicators could be categorized into SBS degradation cluster and asphalt oxidation cluster. I PB and I SBS were categorized into the SBS degradation cluster, whereas I C O , I S O , PDI , and I C belonged to the asphalt oxidation cluster; the classification of R a and R q varied depending on the aging conditions. These findings provide a basis for investigating the deterioration of SBSMA in plateau regions.