Viscoelastic characterizations of aged WER-SBR modified emulsified asphalt under thermal-oxidative aging

Viscoelastic characterizations of waterborne epoxy resin (WER)-SBR modified emulsified asphalt (WESEA) were examined under various thermal-oxidative aging conditions. Dynamic shear rheometer (DSR) tests characterized the rheological properties, while Fourier transform infrared spectroscopy (FTIR) analyzed chemical structural changes. The complex shear modulus (G*) of RTFOT-aged WESEA (R-WESEA) exceeded that of RTFOT-aged SBR emulsified asphalt (R-SBR), and G* increased with WER dosage at a given temperature. The G* aging index (G*after aging/G*before aging) for R-WESEA was lower than that of R-SBR and decreased with rising temperature. Conversely, the phase angle (δ) aging index (δafter aging/δbefore aging) increased with WER dosage, reflecting a gradual shift toward more elastic-dominated behavior. The rutting factor (G*/sin δ) of R-WESEA increased with WER dosage but declined markedly at elevated temperatures. Multiple stress creep recovery (MSCR) tests revealed that increasing WER dosage enhanced the percent recovery (R) while reducing the nonrecoverable creep compliance (Jnr), signifying improved elastic response. Prolonged aging progressively increased G*, with accelerated growth at 80 °C and 100 °C versus 60 °C, suggesting coupled oxidative hardening and WER post-curing. FTIR revealed that the aging-induced increments in the carbonyl (IC═O) and sulfoxide (IS═O) indices in WESEA were significantly lower than those in R-SBR, indicating that WER effectively retarded the formation of oxygen-containing functional groups and stabilized unsaturated bonds, thereby decelerating thermo-oxidative aging. Consequently, WER enhanced the high-temperature performance and long-term durability of emulsified asphalt composites.