Suppressing Actions of Inorganic Flame Retardants on the Pyrolysis Behavior of Asphalt

To understand the suppressing actions of inorganic compound flame retardant (CFR) on the pyrolysis behavior of asphalt, five halogen-free flame retardants, such as expanded graphite, aluminum hydroxide, magnesium hydrate, calcium hydroxide, and microencapsulated red phosphorus, were selected to match the pyrolysis temperature ranges of four asphalt components, respectively. The pyrolysis behaviors, volatile emissions, and pyrolysis residues from asphalt and CFR-modified asphalt (FR asphalt) were compared. Also, the effects of CFR on the microscopic morphology, microstructures, and micromechanical performance of asphalt were analyzed. The high-temperature stability of asphalt is increased by the presence of CFR, and there is a flame-retardant constituent in CFR that suppresses the pyrolysis of each component in the overall asphalt pyrolysis process. Additionally, the FR asphalt pyrolysis process is endothermic. The added CFR retards the asphalt pyrolysis process. The formation of the surface carbon layer impedes heat transfer. Also, the volatile emissions during asphalt pyrolysis are reduced by the presence of CFR. The added CFR promotes an increase in the size of the asphalt microstructure. The surface of FR asphalt becomes rougher and more rugged than that of asphalt. Finally, the elastic modulus, deformation resistance, and micromechanical performance of asphalt are increased as the level of FR presence is increased. FR asphalt has a higher adhesive force, which is conducive to increasing the adhesivity of FR asphalt with mineral aggregate in the FR asphalt mixture.