Low-Temperature and Flame-Retardant Performance of an APP/ZA/TPP Composite in SBS-Modified Asphalt and Mixtures

Abstract To ensure the safety of the driving operation, flame retardants must be applied to the tunnel’s asphalt surface. The problem with the current flame retardants is that they make asphalt less effective at low temperatures, which lowers the quantity of flame retardants needed in asphalt pavement. The main objective of this study was to develop a new type of flame retardant with little impact on asphalt’s performance at low temperatures. A composite flame retardant (TFR) was developed, with a composition of ammonium polyphosphate (APP): zinc aluminate (ZA): triphenyl phosphate (TPP) = 5 ∶ 3 ∶ 1.25 , and its mass fraction in the binder is 9.25%. In contrast to the conventional APP system, ZA is added to this composite flame retardant to provide a smoke suppression effect, and TPP is added to suit low-temperature performance requirements. This study used APP, ZA, and TPP to develop a novel composite flame retardant that performed well at low temperatures. The performance of TFR-modified asphalt at low temperatures was then investigated using low-temperature rheological testing. After that, the ability of TFR-modified asphalt to withstand flames was evaluated, and its combustion residue was investigated using macro and micro morphological analysis. Finally, the low-temperature and flame-retardant properties of the TFR-modified asphalt mixture were validated. Among them, the low-temperature performance was evaluated via tests using a bending beam rheometer (BBR) under the condition of − 12 ° C to − 24 ° C , as well as a force-measuring ductility test (FDT) conducted at 5°C with a tensile rate of 1 cm / min . The flame-retardant performance was assessed through tests in accordance with the Chinese Industry Standard for Limiting Oxygen Index (LOI), the Chinese National Standard for smoke density rating, and a cone calorimeter test (with a radiant flux of 50 kW / m 2 ). A scanning electron microscope (SEM) was used to examine the characteristics of combustion remnants. The outcomes showed how well TFR-modified asphalt and its mixture performed at low temperatures. In comparison to conventional flame-retardant (CFR)-modified asphalt, the tensile flexibility of TFR-modified asphalt was 43.7% higher, the fracture energy increased by 8.3%, the ratio ( m / S ) of creep rate (m) to creep stiffness (S) increased, and the stress relaxation ability improved. Through multimechanism synergy, TFR enhanced asphalt’s flame-retardant ability. Phosphorus-nitrogen synergy boosted heat absorption in the early stages of asphalt burning, but the dense carbon layer impeded heat transfer in the latter stages.