Dynamic Shear Rheometer for rheological investigation of bitumen in road applications : The impact of measurement technique

The rheological properties of bituminous binders tested with a dynamic shear rheometer (DSR) as a function of loading time and temperature can more accurately represent real road situations with rising traffic loads and densities combined with climatic change. This method is more effective than traditional methods such as measuring the softening point and penetration. Complex shear modulus and phase angle which describe the materials’ viscoelastic response at a given frequency and temperature can be measured using a DSR following European standard EN 14770.Even though EN 14770 primarily describes the preparation and conditioning of specimens, various steps in the DSR testing setup result in nonconformity. Therefore, an investigation was conducted to review several areas of test method practices and the underlying impact on results. Data from round-robin tests on bitumen types 20/30 in 2018 and polymer-modified bitumen 45/80-55 in 2019 and 2020, as well as from laboratory experiments on neat bitumen and modified bitumen with wax, SBS, and filler were analysed. The variability in testing conditions and how the testing conditions may affect the measures, as well as the precision of the test technique, are statistically examined. After that, a two-level, three-factor experimental design was used to investigate the effects of the oven setting temperature (HT), bonding temperature (BT) to the rheometer, and trimming state of the specimen on outcomes. Finally, DSR and conventional tests were used to examine the stiffening impact of the fillers when added to bitumen (mastics).The results based on round-robin test data demonstrate an improved precision on measured |G*| and δ discarding data from inappropriate plate geometry. It was discovered that when using PP25, the BT and HT had a considerable impact on the results, whereas when using PP08, the trimming state significantly affected the measured parameters. The HT showed higher material type dependency compared to Trim and BT. The mastic results from DSR and traditional tests are somewhat in agreement and can be related to the properties of the filler. However, determining a temperature at which |G*| achieves a particular value and its corresponding δ would be useful for the universality of the result expression.According to the findings, a thorough standard for specimen preparation and test setup that is strictly followed can enhance the uniformity of DSR testing. Since these empirical tests are insufficient to characterise and choose material based on desired criteria in today's demanding conditions and eventually reduce maintenance work, it is advantageous to have specifications that consider more than only the penetration and softening point for bitumen and mastics.