Effect of phosphorus-nitrogen flame retardants on VOCs emissions and properties of SBS-modified asphalt

This study investigates the effects of two phosphorus–nitrogen flame retardants, ammonium polyphosphate and melamine polyphosphate, on the VOC emissions, flame retardancy, and rheological properties of SBS-modified asphalt binder. Through systematic testing across dosage levels from 0.5 to 2.0 wt percent, we found that melamine polyphosphate consistently outperforms ammonium polyphosphate in suppressing volatile organic compounds. At its optimal dosage of 1 wt percent, melamine polyphosphate achieves a VOC inhibition efficiency of 44.12 %, compared with 34.68 % for ammonium polyphosphate at 0.5 wt percent. The superior performance of melamine polyphosphate arises from its larger specific surface area and stronger phosphorus–nitrogen synergistic effect, which enhance catalytic oxidation and gas-phase dilution during thermal decomposition. In addition, melamine polyphosphate raises the limiting oxygen index above the required threshold for tunnel pavements, delays ignition, and reduces carbon monoxide emissions. Rheological tests indicate that the recommended 1 wt percent dosage improves high-temperature deformation resistance while moderately affecting low-temperature crack resistance. We therefore propose melamine polyphosphate at 1 wt percent as an effective additive for achieving fire safety and VOC mitigation in tunnel pavement applications without substantially compromising mechanical performance.