An atomistic model of aged asphalt guided by the oxidation chemistry of benzylic carbon with application to asphalt rejuvenated with a triglyceride

QH Chang and EAO Iii and S Ghos and M Zaman and LL Huang and XR Wu, CONSTRUCTION AND BUILDING MATERIALS, 400, 132743 (2023).

DOI: 10.1016/j.conbuildmat.2023.132743

Waste cooking oil (WCO) shows promise for restoring physical properties of aged asphalt binder to enable pavement recycling. Its use as a rejuvenator lessens the environmental burden on land fills with its disposal. In this study, we report our initial development of an aged asphalt model and the computational investigation of the effect of triglycerides, the main component of WCO, on the viscosity, self- diffusion, and microstructural properties of aged asphalt at 1 atm and 404 K. The fundamental research question in this work involves understanding the underlying mechanism(s) by which WCO rejuvenates aged asphalt binder. A central feature of this aged asphalt model is consideration of oxidation chemistry and reported functional group concentrations since properties like viscosity are known to be related to the amounts of moieties such as ketones and sulfoxides. Model oxidation compounds include proposed representative asphalt structures based on Peterson's dual reaction pathways, leading to polycyclic aromatic hydrocarbon molecules resulting from fast phase aromatization and multiple species from a slow phase degradation of benzylic hydroperoxide intermediates. The new model takes into account the observed product distribution of aryl alcohols and aryl ketones based on findings for cumene oxidation in the literature. Other oxygen-containing functional groups, such as anhydrides, carboxylic acids, and polynuclear aromatics, have been incorporated to account for the critical physical characteristics of aged asphalt. By extending the molecular basis set of asphalt components, we can now construct more realistic asphalt models to represent varying SARA (Saturates, Aromatics, Resins, Asphaltents) content, different oxidation levels and functional group composition. Virtual representations of the molecules in the basis set were created and molecular dynamics simulations of the aged asphalt model conducted. Results with aged asphalt basis set provided good agreement with reported physical properties. With the developed aged asphalt model, our molecular dynamics simulations reveal that triglyceride (tristearin) has preferential interactions with asphaltene molecules. On addition of 10 wt% triglyceride to aged asphalt, the asphaltene-asphaltene interaction was most significantly affected. The radial distribution functional analysis revealed that the asphaltene-asphaltene nearest neighbor distance increased from 4.0 & ANGS; to 7.5 & ANGS;. Thus, adding triglyceride to aged asphalt helps to reduce the aggregation of asphalt components and as such promotes a decrease in viscosity of the aged asphalt, from 83 cP to 69 cP. In addition, the asphaltene components have larger self-diffusion coefficients upon the addition of triglyceride, changing from 3.57 x 10-8 cm2/s in the aged asphalt to 1.41 x 10-7 cm2/s in the triglyceride/aged asphalt mixture. Those findings are consistent with the observed effectiveness of utilizing waste cooking oil to rejuvenate aged asphalt.

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