Nebraska Balanced Mix Design - Phase II

This study aimed to propose a performance-based framework to evaluate highly recycled asphalt mixtures containing polymer-modified binders for potential use in a balanced mix design (BMD) specification in the state of Nebraska. For that, loose and compacted mixtures were directly collected from plant and field projects within a benchmarking study, subjected to an extensive experimental program. The laboratory investigation employed different monotonic tests recommended in BMD Phase 1, as well as the dynamic modulus test. Three long-term aging protocols were investigated in terms of their impact on the mechanical, rheological, and chemical characteristics of asphalt mixtures and binders. Moreover, field assessments with cores and pavement management system data were added to the analysis. Results evaluated the sensitivity and significance of various tests for characterizing rutting and cracking resistance across mixtures varying in binder sources, grades, recycled contents, and warm mix additives. The variability and discrimination potential of performance-based parameters were identified, and suitable performance tests were suggested for the BMD framework considering the type of mixtures and site conditions of this study. The preliminary threshold criteria for each performance test were selected using a mechanistic-empirical approach considering three representative structural layers. Regarding the aging protocol, while the studied aging protocols yielded similar cracking resistance trends, their aging severity differed. Considering mechanical, chemical, and rheological similarities, an adjusted long-term aging protocol was selected for the potential implementation in the state’s BMD framework. Reheating and dwelling time impacted performance indices, showing they could be considered in criteria selection. The selected performance-based parameters and threshold criteria corroborated with the results from field rutting, roughness, and cracking assessments, which further verify the outcomes. It was recommended to validate the selected performance tests, associated preliminary criteria, and aging protocol using more extended field data collection.