Investigating Nonlinear Fatigue Damage Evolution of SBS-Modified Asphalt Mixtures with Physical Gel Structure

Styrene-butadiene-styrene (SBS) modifier can enhance the resistance of asphalt mixtures to load-induced deformation and fatigue cracking by constructing a three-dimensional physical gel network. However, a rigorous mechanical characterization of this mechanism remains lacking. This study elucidates the nonlinear fatigue damage evolution of SBS-modified asphalt mixtures with physical gel structures based on residual strain response analysis. Indirect tensile fatigue tests were conducted to characterize the residual strain response of SBS-modified asphalt mixtures. A damage-informed residual strain model was established, and a relative residual strain change rate was defined to analyze the correlation between fatigue cracking and residual strain response. Furthermore, the nonlinear fatigue damage evolution of SBS-modified asphalt mixtures was investigated based on the fatigue damage theory. The results demonstrate a strong correlation between fatigue cracking and a viscoplastic strain in the SBS-modified asphalt mixtures. The proposed residual strain model accurately describes the nonlinear fatigue damage evolution and residual strain response. The relative residual strain change rate serves as a rational indicator of the material’s resistance to fatigue cracking and residual strain accumulation. The SBS modifier enhances resistance to residual strain and fatigue cracking by forming a complex polymer network that establishes a three-dimensional physical gel structure.