Impact of asphalt aging temperature on chemo-mechanics

As the use of warm and cold asphalt mixing technologies provides an opportunity to save energy during production, it is important to determine if this lower mixing temperature also has a long-term effect on the binder chemical and rheological properties and performance. In this study, a link between the chemistry and rheology of bituminous binders with a focus on short-term aging temperature is proposed. This link is made using a rheological aging index (RAI), the crossover temperature and a chemical aging index (CAI). The RAI is calculated using the difference in the integration areas under shear modulus master curves generated from Dynamic Shear Rheometer (DSR) data on unaged and aged bitumen. The cross over temperature is defined as that when the material transitions from elastic to viscous behaviour. The CAI is obtained from Fourier-transform infrared spectroscopy (FTIR) measurements by combining the carbonyl and sulfoxide indices. In addition, the effect of aging on the molecular size distribution of the binders was evaluated using Gel Permeation Chromatography (GPC). Two asphalt binders from two sources at two RTFOT aging temperatures 123 °C and 163 °C corresponding to warm mixing and hot mix mixing temperatures respectively were used. The rheological aging index, the chemical aging index and GPC delivered the same trends, showing that the short-term aging temperature has a significant effect on long-term chemical and rheological properties. The extent of this depends on the source as some binders were identified as being more aging resistant.