Mechanism of a Warm-Mix Agent and Its Effects on the Rheological Properties and Thermal Stability of Aluminum Hydroxide and Organic Montmorillonite Composite Flame-Retardant Asphalt

The effects of a warm-mix agent, PN2217, on the rheological properties and thermal stability of alumina trihydrate/organic montmorillonite (ATH/OMMT) composite flame-retardant asphalt were investigated in this study. Dynamic shear rheological and multiple stress creep recovery tests were performed to investigate the high-temperature rheological properties of ATH/OMMT flame-retardant asphalts with different amounts of PN2217. Thermogravimetry–differential scanning calorimetry was performed to evaluate the thermal stability of the asphalt binders. Kinetic analyses were conducted to investigate the combustion mechanism. Fourier-transform infrared (FTIR) spectroscopy and atomic force microscopy were performed to investigate the reaction mechanism of PN2217 with the ATH/OMMT flame-retardant asphalt. The microstructure of the combustion residue was analyzed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The FTIR spectra revealed no chemical change after the addition of PN2217 to the flame-retardant asphalt. The results indicated that PN2217 adversely affected the elastic response and rutting resistance of the ATH/OMMT asphalt because the intercalated structure formed by the intercalation of the asphalt molecules into OMMT was transformed into a phase-separated structure in the presence of PN2217. Moreover, PN2217 adversely affected the thermal stability of the ATH/OMMT asphalt by reducing the activation energy and preventing the formation of a char layer during combustion.