Multi-Index Stage-Based Characterization and Residual-Life Estimation of Splitting Fatigue Damage in Asphalt Mixtures

To overcome the inability of single life-based indices to represent the nonlinear degradation of asphalt-mixture bearing capacity, this study proposes a multi-index framework for splitting-fatigue damage characterization and residual-life estimation. AC-13C mixtures were tested through indirect tensile strength, constant-amplitude splitting-fatigue, and post-fatigue residual-strength tests. The framework integrates the life-based damage index Df, residual strength ratio λ, performance damage index Ds, damage lag coefficient L, and peak displacement response, thereby distinguishing life consumption, strength loss, deformation amplification, and their asynchronous evolution. A constrained three-stage residual-strength decay model was further established to identify damage position from measured residual strength and estimate the residual-life ratio, providing greater interpretability and predictive utility for damage-position inversion and residual-life estimation than single-index or single-stage approaches. Under S = 0.3, 15 °C, and 10 Hz, damage stages were preliminarily bounded by D1 = 0.50 and D2 = 0.65. From Df = 0.20 to 0.80, λ decreased from 0.928 to 0.380, while peak displacement increased from 3.076 to 4.788 mm; the late-stage attenuation and deformation rates were 4.23 and 4.44 times those in the middle stage, respectively. The model achieved R2 = 0.9942, RMSE = 0.0158, and MAPE = 2.06%, demonstrating reliable damage characterization and residual-life inversion.