An Attempt to Distinguish Thermal from Oxidative Ageing of Asphalt Binders by NRTFOT

The ageing of asphalt pavements in the field is a thermo-oxidative degradative process that occurs over the pavement service life resulting in increase of stiffness and brittleness and thus, a decrease of resistance to fatigue and thermal cracking. Asphalt ageing can be separated into two phases, short-term (STA) and long-term ageing (LTA), respectively. STA occurs during the production and construction of the asphalt mixture. The high temperatures considered in those processes culminate in loss of volatile compounds and oxidation of the asphalt binder. The subsequent incorporation of oxygen into the asphalt binder is a slow oxidation mechanism related to the LTA during the service-life of a pavement. This study aims to understand and distinguish the effect of temperature and oxygen in the STA of a paving grade bitumen 70/100. For this purpose, the sample was short-term aged considering two distinct ageing procedures, the rolling thin film oven test (RTFOT) and a modified version of nitrogen rolling thin film oven test (NRTFOT). NRTFOT test considers the same procedure adopted in the RTFOT test, except that instead of air, nitrogen is blown into the oven to prevent any oxidative ageing. Fourier transform infrared spectroscopy (FTIR) and mass loss were considered to evaluate the ageing undergone by the asphalt binder during RTFOT and modified NRTFOT procedures. The asphalt binder aged in a nitrogen atmosphere has presented a reduction of its mass after the modified version of NRTFOT procedure. Standard RTFOT resulted in the increase of the material mass. The reduction in mass indicated that the binder only lost volatiles during the ageing in the modified version of NRTFOT; however, according to the infrared spectra, formation of carbonyl and sulfoxides compounds linked to oxidation was observed.