Multi-Stress Loading Effect on Fatigue Response of Asphalt Binder Based on Dynamic Shear Rheometer Testing

Fatigue damage to asphalt pavements due to continuous loading occurs mainly at the binder–aggregate interface or within the asphalt binder. The mechanical response of asphalt binder under variable stress conditions was comprehensively analyzed by repeated loading tests. The viscoelastic intervals of three asphalt binders (Pen70–80, Pen60–70, and SBS) were determined by stress scanning tests, and two different sizes of stresses were selected for constant stress time scanning inside and outside of the intervals based on the experimental thresholds, to provide a reference for the selection of load combinations for variable stress fatigue tests. Cyclic loading of the samples using DSR focused on the complex shear modulus and phase angle behavior of asphalt binder samples under linear viscoelastic (LVE) and nonlinear viscoelastic (NLVE) stresses. The study reveals that under LVE and NLVE stresses, asphalt binders exhibit different mechanical behaviors, each indicating different aspects of damage accumulation and recovery capabilities. Under LVE stress, asphalt binders demonstrate an initial rapid decay of modulus, followed by a phase of slowed degradation and then a swift decline leading to fatigue failure. This pattern contrasts with the response under NLVE stress, where a more pronounced and quicker degradation is observed in both the initial and final phases, indicating significant initial damage. Analyzing the experimental results, at small stresses within the online viscoelastic interval, the modulus decay of asphalt specimens mainly occurs at the late loading stage, and the phase angle growth also occurs mainly at the late loading stage, while at large stresses, the asphalt specimens produce a large amount of modulus decay at the early loading stage. Furthermore, the study explores the NLVE-LVE loading mode, observing a rapid recovery phase in the early stages of the second phase. This phase is characterized by an increase in modulus accompanied by a decrease in phase angle, indicating an increase in the elasticity of the specimen. However, in the LVE-NLVE mode, a rapid accumulation of damage is observed without a similar recovery phase, highlighting the impact of NLVE stress on inducing irreversible damage. The findings suggest a complex interplay between the type of stress applied and the mechanical response of asphalt binders, with significant implications for understanding the fatigue and recovery behavior of asphalt materials under variable stress conditions. The aim is to investigate the mechanical response and damage evolution law of asphalt binder under repeated loading of variable stress to provide reference for material selection and development of durable pavements.