Investigation on the effect of physical hardening and aging temperature on low-temperature rheological properties of asphalt binder

In this paper, the effect of physical hardening and aging temperatures on the low temperature rheological properties of the asphalt binder is experimentally investigated and modelled. First, Dynamic Shear Rheometer (DSR) tests are performed from -30 degrees C to 80 degrees C on four virgin asphalt binders and the corresponding long-term aged binders, which were previously short-term aged at three different temperatures (123 degrees C, 143 degrees C, and 163 degrees C). Master curves are generated to evaluate the impact of aging temperatures, while the effect of physical hardening is also addressed through a simple testing procedure. Then, Bending Beam Rheometer (BBR) tests are conducted under three different conditioning times (1 h, 24 h, and 72 h) for the same materials, followed by the calculation and comparison of creep stiffness, S(t) and relaxation parameter, m-value. In addition, the Huet model is fitted to the experimental data. Finally, the relationship between the time domain complex modulus based on DSR and the creep stiffness obtained with the BBR at different conditioning time is established, and the critical cracking temperatures are calculated and compared. Results indicate that physical hardening causes a significant increase in complex shear modulus and creep stiffness for DSR and BBR, respectively. This trend is remarkable between the first 60 minutes and 24 h while only a moderate contribution can be observed when conditioning time is extended. Linear correlations can be observed between the DSR and BBR results at different conditioning time. No particular storage time leads to equivalent E(t) master curves for BBR and DSR; the curve of 24 h seems to be a compromise in terms of experimental and time costs. In addition, the reduced aging temperature can significantly mitigate the effect of physical hardening, while only a slight improvement can be found in the aging properties of asphalt binders.