Evaluating the efficacy of laboratory ageing of asphalt mix binders as a prediction for field ageing

Abstract

A Performance-grade Binder Specification (SATS 3208) for South Africa was finalised after CAPSA 2015 and launched at CAPSA 2019. A key feature of the performance-graded binder specification is the regulation of binder performance after long-term ageing, which is simulated in the laboratory using the pressure ageing vessel (PAV). This paper reports how this simulated long-term ageing relates to the ageing of binders in continuously-graded asphalt surfacing mixes in the field. Samples of asphalt surfacing mixes were obtained from ten sites in Gauteng, South Africa, which were constructed 5 to 30 years ago and selected based on the availability of the original binders. An ageing profile was developed for the original binders by characterising their rheology in the original state, after rolling thin film oven (RTFO) ageing and pressure ageing vessel (PAV) ageing after 20 hours, 40 hours and 80 hours. The ageing profiles were compared to the corresponding recovered binders. Rheological parameters used for comparison were Softening Point and Flexural Creep Stiffness / m-Value from the Bending Beam Rheometer (BBR) test.