Nanoporous flame retardants: Toward asphalt with enhanced fire safety and smoke suppression behavior

The fire safety of asphalt gains increasing attention for tunnel asphalt pavements while the high addition amount and function singleness of flame retardants (FRs) highly restricting its widespread application. Herein, a highly efficient nanoporous flame retardants (NFRs) were designed via the zeolitic imidazolate framework -67 (ZIF-67) and magnesium hydroxide (MH) on the surface of diatomite (DA). Various characterizations revealed the piling process of ZIF-67 and MH onto DA surface. The effects of NFRs with multistage nanopore structures on the flame retardancy, smoke inhibition, and rheological properties of asphalt were investigated. Results showed that flame retardancy remarkably improved with the addition of only 5.0 wt% NFRs. The peak heat release rate (PHRR) and total heat release (THR) were reduced by 67.4%, and 40.0%, respectively. The smoke release behavior of asphalt was significantly inhibited. Total smoke production (TSP) decreased by 45.5%. Moreover, NFRs can enhance the rutting resistance performance of asphalt, indicating their potential applications in flame-retardant asphalt tunnel pavements.