Study on the performance of tunnel warm-mix flame retardant asphalt based on macro and micro perspectives

To enhance tunnel fire safety while reducing asphalt mixing temperatures as an alternative to conventional hot-mix technologies, this study developed a novel warm-mix flame retardant composite (DATE) through a water bath rolling adsorption method. The composite synergistically combines zeolite as a warm-mix agent with a decabromodiphenyl ethane-based flame retardant (DAT). A comprehensive investigation was conducted employing thermogravimetric-differential scanning calorimetry (TG-DSC), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), standardised asphalt performance tests, pyrolysis analysis, limiting oxygen index testing, and molecular dynamics simulations. The results show that, compared to zeolite and DAT, the DATE exhibited a wider operating temperature range. Notably, DATE modified asphalt showed improved high-temperature shear resistance. The synergistic effect of the components in DATE raised the pyrolysis temperature of asphalt, and slowed the rate of thermal decomposition, effectively providing flame retardant properties of asphalt. Taking into account both economic and flame retardant performance factors, the optimal dosage was found to be 7% by asphalt mass. At 140°C, the solubility parameter difference between DATE and asphalt was minimised to 0.53 (J/cm3)1/2, indicating the best compatibility. The optimal mixing temperature for asphalt with a 7% DATE content is 140°C. This innovative warm-mix flame retardant improves safety in tunnel construction and operation.