Investigation on Adhesion Characteristics of Virgin-Aged Composite Binder and Binder-Aggregate System

In recycled asphalt mixtures, the RAP binder often becomes stiff and brittle due to aging, making it difficult to achieve a complete integration with the added virgin binder, which could provide a negative impact on the long-term performance of the recycled asphalt mixtures. In an attempt to identify the influence of the integration degree on the adhesion characteristics of virgin-aged composite binder and the corresponding binder-aggregate system, a series of experiments, including the modified boiling test and pull-off test and corresponding formation methods for the binder samples with various interfusion states, were designed and carried out in the present study. The two-layered composite binder (CB), consisting of a layer of virgin binder and a layer of aged binder was fabricated for the experiments, and the testing results were analyzed and compared with those of the virgin binder (VB), the aged binder (AB), and the blended binder (BB). The thermostatic treatments with various durations were subjected to the binder samples to attribute them with various integrations, and the wetting conditioning was also imposed on them to introduce the impact of moisture erosions. The rheological properties, creep recovery capacity, and fatigue resistance of the binders were first investigated based on a dynamic shear rheometer. The adhesion characteristics and failure behaviors of the binder-aggregate system were furthermore explored with the modified boiling test and pull-off test, and the percentage of residual binder (%_residual binder), pull-off test strength (POTS), and moisture damage index (MDI) were adopted to assess or quantify their adhesion characteristics and moisture susceptibility. The results found that the rheological properties and creep recovery capacity of the CB were similar to those of the VB, and its fatigue life exhibited an increasing trend with the extension of the thermostatic-treatment duration. In contrast to the modified boiling test, the pull-off test was more effective at evaluating the integration and distinguishing the failure behaviors of the binder-aggregate system. As the thermostatic-treatment duration prolonged, the interfusion between the virgin and the aged binder was facilitated, the cohesion within the binder and the adhesion between the binder and the aggregate was also enhanced, and thus the adhesion performance and moisture-damage resistance of the system were improved.