Analysis of 4-mm DSR tests: calibration, sample preparation, and evaluation of repeatability and reproducibility

Rheological characterisation methods are important when it comes to a performance-based selection system for bituminous binders for road applications. Standardised methods exist for the determination of bitumen rheological behaviour based on a dynamic shear rheometer (DSR) at intermediate and high service temperatures and a bending beam rheometer (BBR) at low temperatures. Recently, a dynamic shear rheometer with 4 mm parallel plates (4-mm DSR), has been proposed by Western Research Institute (WRI), as a promising method to determine the rheological behaviour at low temperatures. Clear advantages of the 4-mm DSR are related to the small sample size, especially important for recovered and aged binders, and the ability to work with adequate stresses at very low temperatures. Furthermore, if 4-mm DSR can be used to assess the low temperature behaviour of bitumen, then the performance of a binder in the whole range of service temperatures, could be assessed by just one equipment, a DSR. This paper focuses on the challenges related to 4-mm DSR tests regarding equipment preparation, with a specific attention to the temperature assessment and calibration. Furthermore, a sample preparation method, assuring good adhesion to both plates is proposed and the repeatability and reproducibility of 4-mm DSR tests is evaluated.