Asphalt Binder Laboratory Short-Term Aging – Phase II

While blending hot asphalt binder and aggregates in the plant, transporting, and laying the asphalt mixture, hardening of the binder can potentially occur due to the loss of volatiles and/or oxidation. This process is known as short-term aging. According to Parmeggiani, two reactions contribute to short-term aging. In the first reaction, loss of volatiles occurs through evaporation. The rheological properties of the less volatile binders change less and accordingly, they have a higher stability compared to highly volatile binders. The second reaction is oxidation, which is directly affected by the extent of the first reaction. A binder with higher stability has a lower loss of volatiles, which means that its degree of oxidation is lower, and eventually less hardening occurs for such binder. A survey on previous literature indicates that the effects of time and temperature have been in the center of attention in the study of short-term oxidative aging. However, the proper choice of the value of short-term aging parameters (i.e., time, temperature, airflow rate, and weight of binder poured in Rollin Thin Film Oven (RTFO) jar) is necessary for a successful simulation of short-term aging process especially when these parameters can be influenced by the other parameters (i.e. the interactions). On the other hand, it is reported that the RTFO can adequately simulate the short-term aging; however, the current RTFO protocol is inefficient in the simulation of highly viscous binders (the polymer modified asphalt binders and Performance Grade (PG) 70-XX and higher) due to improper dispersion throughout the bottles and creeping of highly viscous binder out of the bottles during rotation. In addition, there are some doubts about the capability of RTFO in the simulation of the oxidative aging process that occurs during warm mix asphalt (WMA) production. Also, the capability of RTFO protocol to accurately mimic the short-term aging of asphalt binders treated by recycling agents (RAs) is questionable. The PI and Co-PI proposed a research project entitled “Asphalt Binder Laboratory Short-Term Aging” to statistically investigate the effect of time, temperature, airflow rate, and asphalt binder weight on the chemical and rheological properties of different asphalt binders in the laboratory short-term aging (RTFO) process. In addition, it was attempted to find an improved RTFO aging protocol, which was applicable on both unmodified and highly modified binders. The statistical analysis showed that the first order terms of time, temperature, and weight as well as their interactive terms were statistically significant. However, the effect of airflow rate, within the studied range, was insignificant. Based on the findings of the first part of the study, a new/improved protocol was proposed in which the aging duration reduced to 45 min while the temperature increased to 180°C. In addition, only 25 g of binder and an airflow rate between 3 and 5 L/min were required for conducting the new short-term laboratory-aging process. According to the obtained rheological properties as well as the chemical characteristics, it was shown that the proposed laboratory short-term aging protocol not only can reduce the aging time of the conventional protocol, but also that is applicable to both neat and polymer-modified modern asphalt binders. In continuation with the previous research project, finding short-term aging parameters (i.e., new/improved protocol) that can properly simulate the aging process that occurs during WMA production is vital since nearly all of the asphalt mixtures in our state are produced using WMA technology. Also, there is a need for better understanding of short-term aging of asphalt binders treated by RAs since NDOT is planning to use these chemical additives in the Nebraska asphalt mixtures in the near future.