Low-temperature creep behavior and microstructural characteristics of photocatalytic N-TiO2-modified asphalt under salt freeze–thaw cycles

Abstract

This study investigates the low-temperature characteristics and the potential for sustained degradation of automotive exhaust of photocatalytic nitrogen-doped titanium dioxide (N-TiO₂) modified asphalt under salt freeze–thaw cycles. Ductility and bending beam rheometer (BBR) tests were conducted to assess the influence of temperature, N-TiO₂ dosage, and salt freeze–thaw cycles on the low-temperature performance of 90# road petroleum asphalt. Atomic force microscope (AFM) and Fourier transform infrared spectroscopy (FTIR) were utilized to analyze the apparent morphology and underlying mechanisms. Finally, exhaust degradation tests were conducted to analyze the exhaust degradation efficiency of the photocatalytic asphalt. The results showed that as the temperature decreased, the N-TiO₂ dosage increased, and the freeze–thaw cycles progressed, the dissipation time of temperature stress within the asphalt prolonged. With increasing N-TiO₂ dosage, the size of the bee phase in the apparent morphology images decreased, while their number increased, leading to greater stiffness of the asphalt system. The N-TiO₂ bonded with hydroxyl groups, resulting in the breakage of CC bonds and an increase in the content indicators of sulfonate and aliphatic compounds. Oxidation and polymerization induced by salt freeze–thaw cycles altered the content indicators of sulfoxide, aromatic, aliphatic, and sulfonate functional groups, with no significant change in the carbonyl group. In exhaust degradation tests, the influence of light intensity on the catalytic rate of N-TiO₂-modified asphalt varied with N-TiO₂ dosage, revealing a peak dosage for optimal performance. Importantly, the salt freeze-thaw cycles process does not affect its photocatalytic efficiency.