Effects of flame retardants on thermal decomposition of SARA fractions separated from asphalt binder

To better understand effects of flame retardants on thermal decomposition of saturates, aromatics, resins and asphaltenes (SARA) fractions in asphalt binder, different flame retardants were selected to match the thermal decomposition temperature range of each SARA fraction, respectively. Then inhibitory effects of matched flame retardants were discussed and microscopic morphology of combustion residues were observed. The results indicate that the decomposition process of each SARA fraction still includes two thermal mass loss stages after adding the matched flame retardants. However, the thermal decomposition rates are lowered, and the initial decomposition temperatures and maximum decomposition temperatures of each SARA fraction are elevated. Also, the matched flame retardants have few effects on the volatile constituents of four SARA fractions, but show an obvious influence on the release amount of gaseous products. CO2 and H2O are still the two main products of each SARA fraction after adding matched flame retardants. Few chemical reactions between SARA fractions and flame retardants are found during their decomposition. Additionally, the superposed and densified charring layers are formed due to the synergic effects of the composite flame retardants. The thick charring layer prevents the heat from transferring, and hinders the oxygen supply, and inhibits the release of flammable volatiles. Finally, the thermal stability of each SARA fraction is greatly improved by the matched flame retardants. The composite flame retardants show a synergistic flame retarding and smoke suppressing effects. This study is beneficial to develop new composite flame retardants for asphalt binder with a satisfactory flaming retarding and smoke suppressing effects.