Flame Resistance of Asphalt Mixtures with Flame Retardants through a Comprehensive Testing Program

Abstract

As tunnels are now longer and built more frequently, fire safety in tunnels has become a major issue throughout the world. The objective of this study is to investigate the flame resistance of warm-mix asphalt mixtures with flame retardants through a comprehensive testing program. In this study, a compound flame retardant (FR) was added to the asphalt and warm-mix asphalt. The comprehensive testing program included the flash point test and oxygen index test of the asphalt binder, the combustion test of loose and compacted mixtures, and a bench scale apparatus for combustion testing of asphalt mixtures in order to understand the flame resistance of the asphalt and mixtures. The results of the asphalt binder tests indicate that FR has no significant effect on the flash point but has an obvious effect on the fire point, and FR asphalt requires more oxygen because the FR prevents it from burning. During various combustion tests, the FR reduced the flame, lessened the smoke, and lowered the temperature but noticeably increased the burning time. It was noticed that the structural integrity of the burned FR mixture samples is preferable to the mixture without FR. The bench scale apparatus for combustion testing shows that the ignition time is extended, both the heat release and smoke for the FR mixtures are noticeably decreased, and both the carbon monoxide (CO) and carbon dioxide (CO2) emissions are reduced. This means FR mixtures have better flame resistance and will have less potential for environmental pollution. Moreover, the results also show that a warm-mix asphalt additive has little effect on the flash point, fire point, or oxygen index of the asphalt. It also has little effect on the burning time and the flame height of loose mixtures. Because the warm-mix asphalt additive aids combustion, it decreases the maximum temperature and mass loss of the compacted mixtures during the firing process. It also shortens the ignition time and decreases the released heat, the total smoke, and the release of CO and CO2. Thus, the flame resistance of warm-mix asphalt with FR is the best due to the combined effect of the FR and the warm-mix asphalt additive, which means that the combination of modified asphalt is preferable for asphalt pavement in tunnels.