Comparison between bitumen aged in laboratory and recovered from HMA and WMA lab mixtures

Oxidative ageing is an important phenomenon affecting asphalt concrete. Currently, binder short-term ageing, occurring during mixture production and laying, is simulated worldwide through rolling thin film oven test (RTFOT), which was developed assuming that the mixture is produced at conventional hot mix asphalt (HMA) temperatures around 160 °C. However, since ageing is strongly influenced by temperature, lower production temperatures imply less material ageing so that the introduction of warm mix asphalt (WMA) technologies could potentially require some adjustments in the ageing simulation procedures. This study aims at determining which RTFOT temperature simulates WMA short-term ageing more closely. To this end, the chemical and the mechanical characteristics of one type of bitumen, recovered from two asphalt mixtures (WMA and HMA) prepared and short-term aged in laboratory, were compared to those of the same virgin binder short-term aged in laboratory with RTFOT at different temperatures (123 °C and 163 °C). Both conventional and rheological tests show higher ageing levels for the binder recovered from HMA with respect to the binder aged with RTFOT at 163 °C, whereas the binder recovered from WMA generally provides an ageing level lower than the binder aged with RTFOT at 163 °C. These results are also confirmed by the chemical analysis using FTIR which indicate higher oxidation levels for the hot mix process compared to the warm mix. These preliminary results confirm that it is necessary to identify an appropriate ageing temperature for the short-term ageing simulation of WMAs with RTFOT.