Combination Design and Performance Evaluation of Warm-Mix Flame-Retardant Asphalt Binder

The application of warm-mix flame-retardant asphalt (WF-A) in narrow confined environments can help reduce the fire hazard of tunnel pavements. This study aims to determine the optimum combination scheme of a developed WF-A that has good flame retardancy and warm mixing performance. The influences of flame retardant (FR) and warm-mix (WM) agent on physical properties of styrene-butadiene-styrene (SBS)-modified asphalt binder were studied through penetration, softening point, and ductility tests. Then, the flame retardancy and smoke suppression were investigated through limiting oxygen index (LOI) tests, while the warm mixing effect of WM agent was evaluated through Brookfield viscosity testing. Finally, the optimal WF-A scheme was determined through the synergistic effect of FR and WM agent on the improvement of flame retardancy and smoke suppression of asphalt binder, and the degree of the adverse effects on the physical properties of asphalt binder. In addition, the warm mixing performance of the optimal WF-A scheme was tested. The selected optimum WF-A was obtained by the content ratio of SBS-modified asphalt binder, 20% aluminum hydroxide (ATH), and 0.6% surface-active WM agent (labeled as SWM). Compared with SBS-modified asphalt binder, the WF-A has better flame retardancy, smoke suppression, and warm mixing performance. It improves the LOI by 49% and reduces smoke density by 26.9%. The mixing and compaction temperatures of the WF-A mixture are reduced by 29°C and 32°C, respectively. This study provides a reference for future studies on the design of WF-A combination ratios.