Comparison of Short Term Laboratory Ageing on Virgin and Recovered Binder from HMA/WMA Mixtures

Abstract

Oxidative ageing strongly affects asphalt mixture behavior. The Rolling Thin Film Oven Test (RTFOT) is currently used to simulate within a laboratory environment the binder short-term ageing, assuming that the mixture is produced at conventional Hot Mix Asphalt (HMA) temperatures (ca 160 °C). However, the introduction of Warm Mix Asphalts (WMAs), which are produced at lower temperatures than HMAs, could require adjustments in the short-term ageing simulation procedure as ageing is strongly influenced by the mixing and compaction temperatures. In this study, the physical properties of a straight-run bitumen, before ageing and after RTFOT ageing at two temperatures (123 °C and 163 °C), are compared to those of the same bitumen recovered from a HMA and a foamed WMA, both produced in laboratory. This comparison aims at determining the best RTFOT temperature for short-term ageing simulation for WMAs. To this end, all the binders were investigated through conventional (penetration value at 25 °C and softening point temperature) and rheological (frequency sweeps with dynamic shear rheometer) tests. Both conventional and rheological tests indicate that the WMA recovered binder is less aged than the binder aged at the standard conditioning temperature of 163 °C, whereas the HMA recovered binder is more aged than the artificially aged binder in the laboratory with RTFOT at 163 °C. These initial results support the idea that an appropriate ageing temperature for RTFOT short-term ageing simulation of WMA needs to be identified.