Deacidified waste cooking oil for asphalt rejuvenation: A multi-scale study of reinforcement mechanisms

With the pressing demand for carbon-neutral infrastructure, the development of green and high-efficiency rejuvenators to restore aged asphalt performance and valorize waste resources has emerged as a central challenge in sustainable pavement engineering. This research evaluates the rejuvenation efficiency of virgin and modified waste cooking oils (WCO and MWCO) from the perspectives of macroscopic rheological performance, microstructural characteristics, and molecular interactions, while elucidating the multi-scale enhancement mechanism of MWCO. The high-temperature deformation resistance, intermediate-temperature fatigue resistance, and low-temperature crack resistance of the rejuvenated asphalts (RAs) were assessed using a dynamic shear rheometer, bending beam rheometer, and multiple stress creep recovery tests. Infrared spectrum and atomic force microscopy were combined to analyze the evolution of chemical functional groups and surface morphological features. Molecular dynamics (MD) simulations were conducted to reveal intermolecular interaction mechanisms through parameters such as radial distribution function (RDF), mean square displacement, and free volume fraction (FVF). The results indicate that MWCO exhibits superior rejuvenation performance compared to WCO. Specifically, MWCO reduced the high-temperature failure temperature of aged asphalt by 7.8 °C, restoring the performance grade from “E” to “S” at 64 °C, identical to the virgin binder. In terms of low-temperature cracking resistance, MWCORA achieved a creep rate of 0.31 at −24 °C, satisfying the SHRP specification, whereas WCORA failed to meet this criterion, demonstrating superior stress relaxation capacity. Spectroscopic analysis confirms better compatibility between MWCO and aged asphalt, along with a more pronounced reduction in oxygen-containing groups (carbonyl index reduced by 38.5% for MWCORA vs. 25.0% for WCORA). Additionally, MWCO more effectively refined the massive bee-like structures and reduced surface roughness. MD simulations demonstrate that MWCO reduced the RDF peak height at 1.11 Å from 9.21 (aged asphalt) to 8.70, merely 0.06 higher than virgin asphalt (8.64), indicating nearly complete restoration of molecular packing order, while significantly enhancing molecular mobility (diffusion coefficient increased by 72.4% compared to aged asphalt) and FVF.