Interpreting the effectiveness of antioxidants to increase the resilience of asphalt binders: A global interlaboratory study

The design and use of antioxidant additives to reduce or slow down the aging of asphalt binders can bring about tremendous benefits to the asphalt industry. Despite many isolated and scattered research efforts showing mixed results, the application of this science to engineering-based solutions has been limited due to variability in results and conflicting data available. This work presents the results from a global interlaboratory study to test the effectiveness of promising antioxidant additives, namely kraft lignin, calcium hydroxide, zinc diethyldithiocarbamate and phenothiazine to increase the resilience of asphalt binders and provide insights towards understanding the complex intricacies between chemistry and rheology. Specifically, seven different binders from various geographical regions in the world i.e., Texas (USA), Vienna (Austria), Illinois (USA), Antwerp (Belgium), and Delft (Netherlands) were blended with the antioxidants at two proportions. Subsequently, the chemical and rheological properties of the blends were evaluated using Fourier transform infrared (FTIR) spectroscopy and dynamic shear rheometer (DSR). The results indicate that although some antioxidants may reduce oxidation based chemical indices, their effect on rheology is more complicated and possibly related to unique physicochemical interactions in each binder. From a macro-perspective, zinc diethyldithiocarbamate showed promising results with a good correlation between rheology and chemistry for the majority of the binders. These additives or other additives with the same working principles should be investigated further. Additionally, significant research efforts must also be directed towards approaches aimed at understanding mechanisms of interaction and relating results with specific binder compositions.