Effect of halloysite nanotubes (HNTs) and organic montmorillonite (OMMT) on the performance and mechanism of flame retardant-modified asphalt

Nano-clays and flame retardant composite-modified asphalt has obvious synergistic effects, but the effect of nano-clays on the flame retardant properties, rheological properties, and flame retardant mechanism of flame retardant-modified asphalt has not been studied. In this paper, synergistic flame retardants containing nano-clays and targeted flame retardant (TFR) were prepared and used as nanocomposite flame retardant (NCFR) to modified asphalt (NFRMA). Nano-clays are two types of nano-silicate clays: halloysite nanotubes (HNTs) and organic nano-montmorillonite (OMMT). The flame retardant properties, rheological properties, and flame retardant mechanism of NFRMA have been studied. The results show that the two kinds of NFRMA exhibit obvious synergistic effects. Among them, HNTs can significantly increase the limiting oxygen index and self-ignition temperature of flame retardant asphalt, but OMMT can significantly inhibit the generation of smoke in asphalt combustion process. Both HNTs and OMMT can effectively improve the high-temperature performance of asphalt. The effect of HNTs in improving the high-temperature performance of asphalt is more obvious than that of OMMT. At the same time, HNTs can also improve the degradation of low-temperature performance of asphalt by TFR. However, OMMT will further deteriorate the low-temperature performance of asphalt. The flame retardant enhancement mechanism of HNTs and OMMT mainly enhances the flame retardant performance of asphalt through its own decomposition and heat absorption and improvement of the barrier layer structure. HNTs are more efficient in improving the integrity of the barrier layer, while OMMT exhibits better smoke suppression performance.