Investigating fracture behaviors of fiber-reinforced warm-mixed recycled SBS modified asphalt mixtures using the DIC and AE techniques under different loading modes

• Warm-mix rejuvenator and basalt fibers work synergistically to improve fracture resistance in WRAM composites. • Flocculent fibers delayed microcrack initiation; chopped fibers suppressed macrocrack growth. • DIC and AE techniques were integrated to monitor fracture evolution under three loading modes. • Mode I, III, and I/III fractures exhibited distinct AE and DIC strain response characteristics. • AE parameters correlated well with DIC-derived damage factors, enabling quantitative evaluation. To enhance the early-stage crack resistance of warm-mixed recycled asphalt mixtures, various types of reinforcing fibers were incorporated and investigated through a multi-scale analysis. Digital Image Correlation (DIC) and Acoustic Emission (AE), both non-destructive techniques, were utilized to monitor damage evolution in real-time. This study investigates the effects of basalt fiber morphology and fracture loading modes on the fracture resistance and synergistic crack resistance mechanisms of fiber-reinforced warm-mixed recycled SBS modified asphalt mixtures (WRAM-BF). Edge-Notched Disc Bending (ENDB) tests were conducted under mode I, mode III, and mixed mode I/III loading conditions using flocculent and chopped basalt fibers, combined with DIC and AE monitoring techniques. AE signal parameters, including source localization, peak frequency, and ringing counts, were analyzed to characterize the initiation and evolution of internal microcracks. DIC strain field mapping and the damage factor were employed to quantify full-field mesoscale strain distributions and crack propagation. The results indicate that the integration of AE and DIC facilitates a thorough and quantitative assessment of fracture behavior in WRAM-BFs. Specifically, flocculent fibers were found to effectively delay microcrack initiation, whereas chopped fibers significantly suppressed macrocrack propagation under various fracture modes. The findings also offer insights into the toughening mechanisms of fiber–rejuvenator synergy in sustainable asphalt composites.