Flame retardance and fume inhibition of bio-based composite flame retardant on bituminous combustion and its numerical models

To investigate the effects of sustainable bio-based composite flame retardant (BCFR) on flame retardance and fume suppression of bitumen and establish unified combustion models of bitumen and BCFR bitumen, the mass loss and fume release during bituminous and BCFR bituminous combustion processes were studied using thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) tests. Results show that when bitumen burns out, BCFR bitumen remains the residue rates of 33%, 28% and 21% at 5, 10 and 15 °C/min, respectively. BCFR dilutes active free radicals involved in combustion at early bituminous combustion stage, thus reducing the reaction rate, and then inhibits bituminous combustion by forming intumescent char layer, increasing the char yield of bitumen, strengthening the thermal stability of char produced from bituminous combustion. BCFR does not reduce the kinds of fume constituents released from bituminous combustion but inhibits the release of aldehydes and phenols mainly by suppressing the oxidation reaction at early bituminous combustion stage. BCFR can effectively suppress the fumes release amount during bituminous combustion at lower heating rates. The proportions of alkanes and ketones released at the second and third stages of BCFR bituminous combustion are larger than those of bituminous combustion by 9.27% and 5.8% at 15 °C/min, respectively. Although BCFR has limited inhibitory effects on fume release amount at a larger heating rate, it inhibits the volatilization and combustion of alkanes in bitumen. Meanwhile, the combustion models of bitumen and BCFR bitumen established can better reproduce TG test results. This study develops a cleaner and more efficient bio-based flame retardant, and provides a reliable bituminous combustion model for large-scale fire simulation.