Molecular dynamics simulation and experimental validation on the interfacial diffusion behaviors of rejuvenators in aged bitumen

• Published in: Materials & design 2023-02, Vol.226, p.111619, Article 111619
• Main Authors: Ren, Shisong, Liu, Xueyan, Gao, Yangming, Jing, Ruxin, Lin, Peng, Erkens, Sandra, Wang, Haopeng
• Format: Article
• Language: English
• Subjects: Aged bitumen; Diffusion behavior; Experimental validation; Influence factors; Molecular dynamics simulation; Rejuvenator
• ISSN: 0264-1275; 1873-4197
• DOI: 10.1016/j.matdes.2023.111619

[Display omitted] •Molecular dynamics simulation was adopted to predict the interfacial diffusion coefficient of various rejuvenators in aged bitumen.•The experimental results in both magnitude and order of diffusion coefficients agree well with MD simulation outputs.•The magnitude for diffusion coefficients of four rejuvenators varies from 10-11 to 10-10 m2/s, and the diffusive capacity order is Bio-oil > Engine-oil > Naphthenic-oil > Aromatic-oil.•The underlying mechanism comprises the free volume fraction distribution and intermolecular force between the rejuvenator and aged bitumen molecules. This study aims to multiscale investigate the effects of rejuvenator type, temperature, and aging degree of bitumen on the diffusion behaviors of rejuvenators (bio-oil BO, engine-oil EO, naphthenic-oil NO, and aromatic-oil AO) in aged binders. The molecular dynamics (MD) simulation method is performed to detect the molecular-level diffusion characteristics of rejuvenators and predict their diffusion coefficient (D) parameters. At an atomic scale, the mutual but partial interfacial diffusion feature between rejuvenators and aged bitumen molecules is observed. Moreover, Fick's Second Law well fits the concentration distribution of rejuvenator molecules in aged bitumen. The magnitude for D values of four rejuvenators varies from 10-11 to 10-10 m2/s, and the diffusive capacity order is BO > EO > NO > AO. Meanwhile, diffusion tests and dynamic shear rheometer (DSR) characterizations are employed to validate the MD simulation outputs. The experimental results in magnitude and order of D values agree well with MD simulation outputs. Lastly, the increased aging degree of bitumen exhibits a negative impact on the molecular diffusivity of BO, EO, and NO rejuvenators, while the D value of AO molecules enlarges as the aging level deepens. The underlying mechanism may be composed of the free volume fraction in aged bitumen and the intermolecular force between rejuvenator and aged bitumen molecules, which differs remarkably for various rejuvenators.