The influence of geometry and sample preparation on dynamic shear rheometer testing

The dynamic shear rheometer (DSR) can be considered to be one of the most complex and powerful instruments for characterising the flow properties of bitumen. This paper describes an investigation into the influence of three sample preparation methods (hot pour, silicone mould and weighing) and two testing geometries (8 and 25 mm parallel plate) on the rheological parameters measured during DSR testing. The effect of the different sample preparation methods and sample geometry have been evaluated for a series of unmodified (penetration grade bitumen), process modified and polymer modified bitumens. The results indicate that a method involving the pouring of hot bitumen onto one of the plates of the DSR and then trimming the edge of the sample is the most consistent means of sample preparation. In terms of testing geometry, the results show that it is advisable to overlap testing geometries when testing across certain transitionally stiffness regions (approximately 100kPa for the 8 and 25 mm geometries). In addition, the use of Black diagrams of complex modulus versus phase angle provides a useful means of selecting suitable testing geometries. For the covering abstract see ITRD E117840.