Introducing a new specimen shape to assess the fatigue performance of asphalt mastic by dynamic shear rheometer testing

Early failure of asphalt pavements is a common issue all around the world. Damages are caused by various reasons like insufficient binder or aggregate quality, an inadequate mix design or improper handling in the production/construction process. The effects of binder, aggregates and mix design have been widely studied and state-of-the-art testing methods are available for both, hot-mix asphalt (HMA) and for each component. An important part in HMA belongs to the asphalt mastic, where no standardized method is available to allow a quality control. Asphalt mastic is the mix of bitumen with aggregates smaller than 63 (125) µm and covers the coarse aggregates as the actual binding component in the mix. This research aims at developing a testing method for asphalt mastic based on fatigue tests. The dynamic shear rheometer (DSR) was found as a suitable device for this purpose. The DSR fatigue test consists of the 8 mm parallel-plate geometry widely used for binder performance grading with a sample height of 3 mm. Instead of a cylindrical specimen shape, a hyperboloid of one sheet is applied. This shape predetermines the point of failure and prevents adhesion/interface failures between the mastic specimen and the upper or lower DSR stainless steel plate. The specimens are prepared directly in the DSR employing a silicone mould to ensure an exact specimen shape. This test can be applied to all DSR devices without costly changes or additional equipment as long as sufficient cooling capacity and torque can be provided from the DSR. This fatigue test makes it possible to assess the fatigue performance of binders and mastic samples.