Fatigue Behavior and Multiscale Characterization of 100% RAP Warm-Mix Recycled Asphalt Mixtures Under Multifactorial Loading Conditions

To promote high-value utilization of reclaimed asphalt pavement (RAP), this study developed 100% RAP warm-mix recycled asphalt mixtures using a laboratory-synthesized polymer-based warm-mix rejuvenator. The AC-13 gradation was reconstructed through RAP fractionation and recombination, followed by screening and selection of the RAP preheating temperature, mixing temperature, and rejuvenator dosage within the investigated experimental ranges. The selected mixture, prepared at 120 °C preheating, 145 °C mixing, and 2.5‰ rejuvenator by RAP mass, satisfied the investigated laboratory criteria for high-temperature stability, low-temperature cracking resistance, and freeze–thaw moisture stability. Uniaxial cyclic compression tests showed that cyclic compressive failure life decreased with increasing stress ratio and loading frequency, whereas temperature exerted a nonmonotonic effect, with the highest life among the three tested temperatures occurring at 15 °C. Three-way ANOVA identified stress ratio, loading frequency, and temperature as significant factors (p < 0.001), accounting for 64.61%, 24.05%, and 8.97% of the total variance within the investigated factor ranges, respectively. FTIR showed relative changes in oxidation-related spectral indices after rejuvenator addition, while μCT provided complementary characterization of CT-resolvable porosity and void topology. These results demonstrate the laboratory feasibility of the investigated 100% RAP warm-mix recycled mixture and characterize its cyclic compressive response and multiscale structural features without implying a direct causal mechanism.