Advancements in mitigating oxidative ageing in bitumen using zinc diethyldithiocarbamate (ZDC) as antioxidant: evidence from phase 2B of a global interlaboratory investigation

Abstract

The use of antioxidants presents a promising strategy to slow oxidation of bitumen, thereby enhancing the durability of asphalt pavements. While previous interlaboratory collaborative efforts have established first evidence that antioxidants such as Zinc Diethyldithiocarbamate (ZDC) can mitigate bitumen oxidation, an in-depth evaluation is needed to solidify the findings. This study offers a systematic assessment of internationally coordinated efforts in advancing bitumen antioxidation research. ZDC was incorporated at dosages of 3% and 5% using different bitumen samples from diverse geographical regions. High-temperature performance grading, multiple stress creep recovery, frequency sweep, and bending beam rheometer tests were conducted. Statistical analyses were performed to assess the significance of ZDC’s effects. On average, the addition of ZDC increased the nonrecoverable compliance by 0.37 kPa⁻¹ at the dosage of 3% and 0.15 kPa⁻¹ at 5%, but this effect was statistically insignificant. The addition of ZDC mitigated the hardening and relaxation deterioration simultaneously, thereby improving bitumen’s low-temperature performance. Furthermore, ZDC significantly reduced the Glover-Rowe (G-R) parameter, which is associated with extended service life of asphalt pavements. The average ageing index (based on the G-R parameter) of bitumen modified with 3% ZDC was reduced to 36% of that of the unmodified bitumen and further decreased to 30% at a 5% dosage. Beyond this study, it is suggested to investigate the blending temperature, antioxidation mechanism, extended ageing, mixture performance and environmental impact of antioxidants in future research.