Performance and mechanism of lignin and quercetin as bio-based anti-aging agents for asphalt binder: A combined experimental and ab initio study

• FTIR is used to assess the inhibitory effect of anti-aging agents on asphalt aging. • The capability of lignin to inhibit asphalt aging is lower than that of quercetin . • AIMD simulation and DFT method are used to explore aging mechanism of asphalt. • Bond strength and electrostatic potential are important for anti-aging properties. The addition of lignin to petroleum asphalt as a bio-based anti-aging agent has attracted significant attention owing to its antioxidant property and similar molecular structure to asphalt. To guide the structural modification of lignin to improve its performance in inhibiting asphalt aging, we conducted a combined experimental and ab initio study to reveal the mechanism by which lignin competitively blocks the asphalt aging pathway and to identify the factors affecting the anti-aging property of lignin. Fourier transform infrared spectroscopy was used to evaluate the capability of lignin to prevent asphalt aging. Although lignin inhibited asphalt aging, its activity was significantly lower than that of quercetin , which is another natural phenolic antioxidant. To explain the different performances of lignin and quercetin, ab initio molecular dynamics and density functional theory methods were employed to investigate the aging mechanism of asphalt and the anti-aging mechanism of these two natural phenolics. The results indicate that the H abstraction by O 2 or free radicals is important in asphalt aging and triggers other reactions. Phenolic hydroxyls on lignin and quercetin have strong ability for H atom transfer and positive local electrostatic potential, and so they attract and react with oxidants to prevent the latter from abstracting H atoms from asphalt. Quercetin has a higher content of phenolic hydroxyls than lignin and therefore exhibits superior anti-aging activity. Based on these theoretical results, it is suggested to improve the anti-aging capability of lignin by modifying its structure to lower the molecular weight and increase the phenolic hydroxyl content.