Effect of physicochemical properties of lignin on rheological performance and anti-aging mechanisms of lignin-modified asphalt

Conventional asphalt binder undergoes rapid thermal oxidative aging during construction, which accelerates performance deterioration and reduces the environmental resistance of asphalt binders. To address this challenge, this study investigates five types of lignin, including alkali lignin, dealkalized lignin, sodium lignosulfonate, calcium lignosulfonate and enzymatic lignin (EL), as bio-based modifiers to enhance the aging resistance of asphalt binders. The relationships between the physicochemical characteristics of lignin and the performance of modified binders were thoroughly examined using dynamic shear rheometer (DSR), bending beam rheometer (BBR), gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H NMR). The results show that EL exhibits the most effective anti-aging performance due to its low molecular weight, high phenolic hydroxyl content and superior dispersibility. FTIR and GPC analyses confirm that EL suppresses carbonyl and sulfoxide formation and limits molecular weight growth through radical scavenging and sacrificial degradation mechanisms. Moreover, 1H NMR results reveal that EL helps preserve molecular integrity by reducing chain scission and oxidation. This study clarifies the anti-aging mechanism of lignin-modified asphalt and provides a theoretical foundation for developing high-performance and sustainable bio-based binders.