Advanced Mixing Rheometry for Dynamic Shear Rheometer Testing of Highly Heterogeneous Bituminous Binders

ABSTRACT In the era of asphalt mixtures designed with various admixtures and secondary materials, bitumen technologists often encounter challenges in testing new materials and interpreting unconventional results. One such challenge arises with highly heterogeneous bituminous binders (HHBBs), including crumb rubber-modified bitumen, which is widely used despite technical drawbacks such as poor stability during storage at high temperatures in asphalt plants. Similar issues may arise during laboratory-scale high-temperature rotational viscosity testing, in which conventional methods designed for homogeneous binders may not be suitable for HHBBs. This study aims to address these challenges by introducing enhanced mixing rheometry for cup-and-bob systems as an optimal solution tailored for dynamic shear rheometers’ rotational testing of HHBBs. The investigation evaluates two types of HHBBs (an 18 % crumb rubber modified binder and a 6 % polymer-modified binder) by testing them with four different impellers to record possible differences in viscosity measurement trends. Laboratory experiments are augmented by numerical analysis to visually assess the stability of HHBBs during rotational testing. Results from this combined empirical and numerical approach indicate that current rotational measurement standards are inadequate for HHBBs because of poor mixing efficiency. However, the use of the dual helical ribbon (ST-26.5-LPG) stirrer, which exhibits improved mixing performance, appears to resolve this issue. Therefore, the authors recommend adopting this specific testing geometry to obtain more accurate high-temperature viscosity measurements of HHBBs, thereby enhancing the realism of the results.