Inhibitory Effects of Composite Fire Retardant Loaded in Porous Warm-Mix Agent on Asphalt Pyrolysis and Volatile Emission

To reduce air pollution during asphalt pavement construction in road tunnels, and to increase fire safety of asphalt pavement when exposed to a tunnel fire, a porous warm-mix agent (WMA) was used to load composite fire retardant (CFR) for developing fire-retarding-type WMA (FWA). Then, the inhibition behaviors of CFR and FWA on asphalt pyrolysis and volatile emission were investigated by thermogravimetric mass spectrometry and nonisothermal pyrolysis kinetics, among other methods. Results indicate that many pore structures of WMA contain crystal water and provide necessary carrier space for loading CFR to prepare FWA. WMA improves the dispersion of CFR in asphalt. The asphalt pyrolysis is a single-stage thrmal decomposition reaction. The higher heating rate causes asphalt to release more heat and gaseous products. Additionally, the developed CFR effectively inhibits the pyrolysis behaviors of asphalt. As the temperature rises, the four fire retardant constituents in CFR are successively decomposed to synergistically inhibit the pyrolysis behaviors of asphalt in the condensed and gas phases. The mass loss of asphalt and the emission of pyrolysis volatiles are reduced. Also, WMA effectively promotes CFR to form a thicker and more pyknotic carbonization layer on asphalt, obviously improving the fire resistance of asphalt in the condensed phase. FWA modified asphalt has a higher thermal stability than CFR-modified asphalt. FWA hinders the nucleation and aggregation of gaseous products, effectively inhibiting the escape of toxic volatiles from asphalt. Finally, the emission of toxic volatiles at the construction temperature range of asphalt is effectively inhibited by FWA, reducing air pollution during asphalt pavement construction and lowering the harm to the health of construction workers.