The State-of-the-art Review on Evaluation Methods of Asphalt Binder Aging

The asphalt binder is one of the most commonly used construction materials in pavement engineering, and is widely used in highways and urban roads in China. During pavement maintenance, asphalt materials exhibit aging behavior, such as hardening and brittleness, which significantly affects the operational quality and service life of the pavement. To promote the development of asphalt binder aging evaluation methods, this paper considers aging evaluation methods such as macroscopic performance testing, microscopic structure detection, and numerical simulation techniques. The macro- and micro-mechanisms that drive asphalt binder thermo-oxidative aging and ultraviolet aging were analyzed multidimensionally. The scales and application advantages of various evaluation methods were compared. The results show that current laboratory investigation methods for the thermo-oxidative aging of asphalt binders fail to accurately determine the long-term service durability. Thus, there is a great need for standardized laboratory research methods on ultraviolet aging. Thermal-oxidative aging is mainly due to high-temperature thermal decomposition that causes chemical bonds to break. Ultraviolet aging is triggered by the absorption of energetic UV light by groups in the molecule and their conversion from the ground state to the excited state, which leads to the breaking of chemical bonds. Macroscopic performance testing is a direct way to establish a link between asphalt binder aging and performance deterioration. The macroscopic performance testing methods and evaluation indicators for the two types of aging cannot be equated or replaced. Microscopic detection techniques, such as fluorescence microscopy, atomic force microscopy, scanning electron microscopy, Fourier-transform infrared spectroscopy, and transmission electron microscopy, can be used to qualitatively or quantitatively analyze the microscopic evolution process of asphalt binder aging and the aging response of modifiers. The results of molecular dynamics and micromechanical models correspond to the precise conclusions of microscopic investigations, and establish correlations with macroscopic mechanical tests to numerically characterize the aging process of asphalt binders. The results of this study can provide a reference for the microscopic evolution law and macroscopic performance properties of asphalt binders. In actual asphalt pavement maintenance, ultraviolet aging and thermal-oxidative aging occurs simultaneously. Multifactor composite aging simulations based on outdoor asphalt pavement aging monitoring should be the focus of laboratory asphalt binder aging simulation. The establishment of a multiscale asphalt aging dynamic simulation, which combines multilevel aging evaluation indicators and numerical simulation techniques, is the main research direction for the cross-applications of asphalt binder materials and numerical simulation. © 2022 Xi'an Highway University. All rights reserved.