The anti-aging design and prevention of asphalt mixtures based on oxygen diffusion process

Abstract

As an organic material, asphalt binders in asphalt mixtures undergo oxidative aging, leading to increased stiffness and brittleness, thereby impacting various performance-related properties of the mixtures. Although numerous studies have explored the aging of asphalt binders, research on aging-related issues in asphalt mixtures is comparatively limited. Thus, a comprehensive understanding of oxidative aging in asphalt mixtures is imperative. This research aims to quantify the effects of oxidative aging on the fatigue resistance of asphalt mixtures and to investigate the oxidative aging process based on oxygen diffusion. The overarching research goal encompasses four specific objectives: (1) Employing the simplified viscoelastic continuum damage (S-VECD) model to quantitatively analyze the effects of oxidative aging on the fatigue resistance of asphalt mixtures. (2) Monitoring changes in oxygen content within asphalt mixtures and asphalt pavements. (3) Identifying factors that affect the oxygen diffusion coefficient of asphalt mixtures (Ds) and assessing its impacts on oxidative aging. (4) Utilizing the Ds to evaluate the anti-aging performance of various preventive maintenance techniques. To address objective (1), two fatigue indices (DR and Sapp) derived from the simplified viscoelastic continuum damage (S-VECD) model were employed to evaluate the fatigue resistance of laboratory-aged asphalt mixtures. Fourier transform infrared spectroscopy (FTIR) was utilized to evaluate the aging state of asphalt binders extracted from aged mixtures. A strong correlation between aging and fatigue indices was observed, facilitating the quantification of the relationship between aging evolution and fatigue modeling of asphalt mixtures. For objective (2), a laboratory oxygen monitoring system was developed to monitor changes in oxygen concentrations in asphalt mixtures with different designs. Additionally, a full-scale trial pavement section (4 m × 6 m × 0.46 m) was constructed and monitored to understand oxygen concentration changes within pavements and to track temperature and water content in different layers. Results highlighted the significant influence of mixture design on oxygen content distribution. Addressing objective (3), the oxygen diffusion coefficients (Ds) of compacted asphalt mixtures with varying designs were determined. Samples were aged unidirectionally, and the aging state of extracted binders was evaluated. The influences of Ds and air void contents on the aging of asphalt binders in the mixture samples were systematically examined and compared. The study revealed that Ds has a stronger correlation with aging susceptibility compared to air void contents. Finally, objective (4) involved using Ds to evaluate the oxygen retarding efficiency and oxidative aging resistance of preventive maintenance methods. Three typical preventive maintenance techniques, fog seal, slurry seal, and chip seal, were applied to treat asphalt mixtures. Ds values before and after the maintenance treatments were identified. The aging state of asphalt binders at different depths within the asphalt mixture samples were characterized. Results indicated that Ds is a very useful indicator for quantifying the oxygen retarding capacity of maintenance methods, with significant implications for the aging susceptibility of asphalt mixtures. Overall, this study enhances understanding of oxidative aging in asphalt mixtures and offers insights into optimizing mixture design, modeling in-situ pavement aging, and designing anti-aging asphalt pavement maintenance.