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.

Two experimental tools to measure the railway crossing dynamic responses are presented. One system is ESAH-M equipped with a 3-D accelerometer and a speed detection sensor that featured for crossing instrumentation and characterised by fast installation/uninstallation, automatic data recording and processing. The other system is a Digital Image Correlation (DIC) based Video Gauge System (VGS) that record the dynamic displacements of the rail/sleepers. A number of measurements have been performed aiming to explore the feasibility of these experimental tools, establish the relation between the measured dynamic responses and condition of the monitored crossings and estimate the effectiveness of crossing maintenances. The measurements based on crossing instrumentation show that the crossing degradation process can be described using the dynamic responses. The wayside monitoring in different problematic track sections have shown the capability of detecting and quantifying ballast conditions. Both systems will be further applied in long-term monitoring of railway crossings.