Comparative Methodology of Viscosity-Based Classification and Measurement Techniques for High-Temperature Behaviour of Paving Grade Bitumen

The accurate determination of the rheological properties of road bitumen types is essential for the reliable prediction of long-term pavement behaviour. At 60 °C, dynamic viscosity is a key rheological parameter characterising the shear-dependent viscoelastic behaviour of bitumen in the temperature range relevant to in-service pavement loading. This study aims to compare different viscosity determination methods—approximations, capillary viscosity, Brookfield measurement and complex viscosity determined by a dynamic shear rheometer (DSR)—and to analyse their relationships with each other in order to find the best method for bitumen classification. Furthermore, the European and Australian bitumen classification standards are compared in terms of dynamic viscosity and penetration, according to which Australian bitumen types show more stable results, as the CV% is less than 10 percent. The study is based on the testing of Hungarian paving-grade bitumens (B50/70, B70/100) and Australian viscosity-graded bitumens (C170, C320), with the comparison of a total of 191 samples obtained from industrial production. The statistical evaluation of the results obtained with the different methods was based on Pearson correlation analysis and relative deviation analysis. The results indicate that the DSR measurement at 1.6 Hz shows the closest agreement with capillary viscosity, with a linear correlation coefficient of 0.95, and exhibits the strongest overall correlation with the other measurement approaches, whereas the Heukelom equation tends to overestimate the dynamic viscosity. The Brookfield method yielded higher viscosity values in all tests. The study highlights that the results of different measurement methods can only be compared under specific shear conditions, and a DSR-based approach can be more suitable for the introduction of a new European bitumen classification system.