Performance evaluation of waste cooking oil at different stages and rejuvenation effect of aged asphalt through molecular dynamics simulations and density functional theory calculations

Abstract

• Representative models of waste cooking oil at different stages are determined. • When the triglyceride is converted to free acid, the positive electrostatic potential, and cohesive energy density increase. • After chemical treatment, waste cooking oil can improve rejuvenation effects on fraction free volume and diffusion characteristics of aged asphalt. Waste cooking oil (WCO) has received more and more attention as an asphalt rejuvenator. The properties of WCO itself will change with the use of time, affecting its rejuvenation effect on aged asphalt. This paper explored the property changes of WCO with the cooking process and the rejuvenation effect on aged asphalt through molecular dynamics (MD) simulations and density functional theory (DFT) calculations. First, the representative molecules of WCO at different stages were determined. The polarity, basic properties, and solubility parameters of WCO at different stages were discussed. Finally, the thermodynamics properties, binding energy, free volume, and diffusion characteristics of WCO rejuvenated asphalt at different stages were compared. With the cooking process, the triglyceride (TG) is converted into fatty acid (FA), positive maximum electrostatic potential and electrostatic interaction increase, FA has stronger adsorption capacity leads to the reduction of model energy. After chemical treatment, the dipole moment and cohesive energy density of treated fatty acid (TFA) decrease. WCO at different stages can restore asphalt properties, and the surface free energy of asphalt can be better restored by FA. WCO at different stages mainly affects non-bond energy. Compared with FA, the incorporation of TFA has a better rejuvenation effect on the free volume fraction and diffusion coefficient of aged asphalt. The diffusion coefficients in asphalt are respectively: TFA > TG > FA.