| Popis: |
Accurate and relevant rheological characterization is critical for the improvement of current binder specification, modification and formulation strategies, and ultimately the pavement performance. Significant changes have affected the binder quality since the Superpave specification development due to various economic, technical, and environmental motives. This paper assesses the effect of some of these changes on binder rheology. The rheological behavior of binders was investigated by plotting the data in isochronal plots. In these plots, the rheological behavior at a reference frequency is classified into three regions: (1) near glassy region at temperatures below the glass transition temperature (Tg), (2) terminal region at temperatures above the crossover temperature (Tx), and (3) an intermediate “transition” region in between. The intermediate temperature range (TIR) parameter is the difference between Tx and Tg. In this study, Tg and Tx of 30 binders were obtained using 4-mm parallel plates geometry on a Dynamic Shear Rheometer (DSR), and using isochronal plots calculated at various reference frequencies. Additionally, modulated differential scanning calorimetry (MDSC) was used as a widely accepted technique to determine Tg of the binders. In the paper, DSR-calculated Tg at various reference frequencies is compared with MDSC-measured Tg. Tg obtained at a reference frequency of 10 rad/s shows promising correlations with DSC-measured Tg and low-PG temperature based on stiffness (Tc(S)), while Tx at 10 rad/s correlates with low-PG temperature based on stiffness slope, m-value (Tc(m)). Furthermore, TIR correlates with ΔTc, an empirical parameter considered for future specifications in the USA related to cracking. The aforementioned correlations are very promising and provide insights related to the fundamental meaning of the ΔTc parameter and guidelines to formulate binders that meet future specifications. In-depth analysis is ongoing to evaluate how isochronal parameters (Tg, Tx, and TIR) are affected by the reference frequency, and how they relate to binder composition. |
