Halogen-free flame retarded cold-mix epoxy asphalt binders: Rheological, thermal and mechanical characterization

Fire safety of asphalt mixtures in highway tunnels has become a problem of great concerns since asphalt and polymer modified asphalt binders are quite flammable and tend to release poisonous gases and smoke while burning. Therefore, flame retardants are incorporated into asphalt binder to improve the fire retardancy of asphalt mixtures. In this paper, aluminum trihydroxide (ATH) and zinc borate (ZB) were used as halogen-free flame retardants to prepare flame retarded cold-mix epoxy asphalt binders (CEABs). The addition of halogen-free flame retardants increased flame retardancy of the neat CEAB. In addition, ATH-ZB retarded CEAB had higher limited oxygen index (LOI) than single ATH and ZB retarded CEABs at the same content. The presence of halogen-free flame retardants increased the viscosity of the neat CEAB. The viscosity of ATH/ZB retarded CEAB was lower than that of ATH retarded CEAB at a specific content. The incorporation of halogen-free flame retardants enhanced the glass transition temperature of the neat CEAB. Thermal stability of the neat CEAB was improved by the halogen-free flame retardants. ATH/ZB retarded CEAB had better thermal stability than ATH retarded CEAB at the same content. The addition of halogen-free flame retardants increased the tensile strength of the neat CEAB. Uniform dispersion of halogen-free flame retardants in CEABs was observed.