Critical Evaluation of Dynamic Shear Rheometer (DSR)-Based Methods to Measure Asphalt Binder Diffusion

Past studies have proposed various dynamic shear rheometer (DSR)-based procedures to measure diffusion between reclaimed and virgin binders but have noted experimental challenges. Therefore, this study sought to critically evaluate the ability to reliably quantify the rate of diffusion between two binders using the DSR. In these experiments, reclaimed asphalt pavement (RAP) and virgin binder wafers were conditioned in contact. Oscillatory loading was applied to monitor the time-dependent response of the wafer system and infer blending. Experiments in which samples were conditioned within the DSR and external to the DSR were tried. When samples were conditioned within the DSR at hot-mix asphalt production temperatures, poor stress waveform quality precluded the application of oscillatory loading in the DSR using sufficiently low strain amplitudes to prevent mechanical mixing. The use of relatively large, 50-mm-diameter samples did not alleviate the data quality limitations. When samples were conditioned outside of the DSR, mechanical mixing was induced when the samples were transferred from the conditioning chamber to the DSR, which compromised measurements. In the absence of mechanical mixing, time-dependent blending between binder specimens conditioned in contact in the DSR at 120 degrees C was not observed, which suggests diffusion was minimal. Based on the aforementioned observations, the diffusion rate between RAP and virgin binders could not be quantified using the DSR experiments evaluated in this study. Based on the lack of observed diffusion in the absence of mechanical mixing, it is hypothesized that understanding mechanical mixing is critical to inferring blending in RAP mixtures and thus merits further research.