Variable-Amplitude Fatigue Life Prediction of SBS-Modified Asphalt Mixtures with Physical Gel Structures.

The service life of SBS-modified asphalt mixtures with physical gel structures is strongly influenced by the loading sequence-interaction coupling effects. However, conventional linear models fail to accurately capture the influence of such coupling effects on fatigue life. This study, therefore, aims to develop a life prediction method for SBS-modified asphalt mixtures that explicitly accounts for the loading sequence-interaction coupling effects. First, indirect tensile monotonic loading tests, as well as constant-amplitude and variable-amplitude indirect tensile repeated loading tests were conducted to determine the fatigue life of SBS-modified asphalt mixtures under different loading modes. Subsequently, a viscoelastic fatigue damage model was developed to analyze the accumulation of fatigue damage in SBS-modified asphalt mixtures. Subsequently, the effects of loading sequence and loading interaction on the fatigue damage accumulation process in SBS-modified asphalt mixtures were investigated. Based on these analyses, a nonlinear fatigue damage accumulation model considering the loading sequence-interaction coupling effects was established. Finally, a nonlinear fatigue damage accumulation factor was introduced for developing a fatigue life prediction model for SBS-modified asphalt mixtures considering the loading sequence-interaction coupling effects. The results indicate that the low-high (σlow-σhigh) and high-low (σhigh-σlow) loading sequences, respectively, retard and accelerate the fatigue damage accumulation process of SBS-modified asphalt mixtures. Consequently, the corresponding cumulative fatigue life fractions are greater than 1 and less than 1, respectively. Furthermore, the resulting fatigue life is positively correlated with the first-level fatigue life fraction under the σlow-σhigh sequence but negatively correlated under the σhigh-σlow sequence. The developed nonlinear fatigue damage accumulation model can accurately track the nonlinear fatigue damage accumulation of SBS-modified asphalt mixtures. The established nonlinear fatigue life prediction model accurately predicts the fatigue life of SBS-modified asphalt mixtures with physical gel structures under cyclic loading with variable stress amplitudes.