Effects of Elevated Storage Temperature on Reactive Terpolymer-Modified Asphalt: A Low-Frequency Rheological Perspective

This study demonstrates the critical role of test frequency in assessing the deterioration of the upper service temperature rheological properties of reactive elastomeric terpolymer-modified asphalt cements (RT-ACs) during storage. RT-ACs were stored in sealed tubes at 120, 135, 150, and 165 °C for up to 7 days. Significant rheological deterioration was observed at 135 °C and became more pronounced as the storage temperature was increased. After 7 days at 150 °C, the non-recoverable creep compliance increased by a factor of 4.2, while the complex viscosity decreased by 50%. The deterioration was primarily associated with weakened interactions between the RT polymer and asphalt cement during storage. Across the investigated conditions of RT polymer type, asphalt cement grade, and test temperature, deterioration was more pronounced at lower test frequencies (ω < 1 rad/s). Owing to their high molecular weight, RT macromolecules exhibit slow molecular relaxation. The formation of a network between RT and asphalt cement further restricts molecular mobility, due to which the deterioration was primarily observed at lower test frequencies (ω < 1 rad/s). Importantly, storage-induced deterioration of RT-ACs adversely affected the performance of the corresponding asphalt mixtures. After one week of storage at 150 °C, Marshall stability and fatigue life decreased by 20%, indirect tensile strength decreased by 30%, moisture susceptibility increased by 10%, and rut depth increased by 60%. These findings highlight the importance of evaluating RT-ACs at low test frequencies (ω < 1 rad/s) to assess the impact of elevated storage temperatures, leading to reliable quality assessment, classification, and performance evaluation.