Materials Design, Preparation Parameters, and Performance Evaluation of Warm-Mix Flame-Retardant Asphalt

The requirement for flame-retardant and warm-mix materials in asphalt pavement construction has increased, particularly in enclosed spaces. Using five selected flame-retardant raw materials and three warm-mix agents, a comprehensive evaluation of novel composite warm-mix flame-retardant asphalt (WFRA) was conducted, including basic performance tests, limiting oxygen index (LOI) measurements, rheological analyses, and microscopic characterization. The results showed that the composite flame-retardant asphalt exhibited better comprehensive performance then single flame-retardant asphalt. Different warm-mix agents had different effects on asphalt performance. By mixing warm-mix agents with flame retardant, the optimal WFRA formula was obtained based on the entropy weight method, and it was predicted to reduce the mixing temperature by approximately 30°C. The optimal preparation parameters were identified using response surface methodology: shear time of 43 min, shear temperature of 154°C, and shear rate of 2,812 rpm. The rheology test showed that compared with that of virgin asphalt, the high-temperature performance of WFRA was improved by about 30%. The Fourier-transform infrared spectroscopy (FTIR) analysis indicated that the warm-mix and flame-retardant additives merely underwent physical mixing with asphalt, without any chemical interactions occurring. Scanning electron microscopy (SEM) tests showed that the agents formed a complex spatial network structure within the asphalt, which may contribute to flame retardancy and a warm-mixing effect, and simultaneously enhanced the asphalt’s high-temperature performance. The findings of this study have significant implications for the advancement of tunnel asphalt pavements.