Implementation of Asphalt Balanced Mix Design in Oklahoma: Progress, Challenges, and Future Prospects

Abstract

The Oklahoma Department of Transportation (ODOT) has undertaken a comprehensive, multi-phase initiative to implement Balanced Mix Design (BMD) for asphalt pavements, aiming to improve long-term performance, sustainability, and cost-effectiveness. This dissertation documents the development, evaluation, and statewide implementation efforts of BMD in Oklahoma, highlighting the transition from traditional volumetric-based Superpave methods to performance-based specifications. This study began with a critical assessment of ODOT’s pavement performance challenges and the limitations of existing mix design practices. A phased implementation strategy was adopted, involving pilot projects, performance testing, specification development, and stakeholder engagement. Key rutting and cracking performance tests were evaluated for their repeatability, sensitivity, and practicality. Hamburg wheel tracking test (HWTT), which ODOT has used continuously for over a decade, remained an integral part of the BMD framework, and it is intended to be used in conjunction with the ideal cracking test (IDEAL-CT), selected for further evaluation due to its operational simplicity and ease of implementation. Over seven years, four implementation phases were completed. These included 33 pilot and implementation projects across the state with diverse traffic and environmental conditions. Asphalt mixtures were tested under design and production, according to different aging protocols, followed by statistical analyses to evaluate their consistency during both phases and variability within and between laboratories. The dissertation also details the iterative process of developing ODOT’s BMD specifications, including adjustments to reclaimed asphalt pavement (RAP) allowances, short-term aging protocols, and pay factor functions. A public-private partnership model was introduced to address workforce limitations, expand testing capacity, and support field implementation. It also assisted with integrating IDEAL-CT into ODOT’s certification program and deploying field testing infrastructure and statewide training. Additionally, multi-phase benchmarking studies established separate CT-Index thresholds for surface and intermediate mixtures, while round-robin testing across 27 laboratories revealed significant inter-laboratory variability, highlighting the need for standardized specimen preparation and adequate technician training. Furthermore, a long-term monitoring strategy has been integrated into ODOT’s pavement management system (PMS), with ongoing data collection on cracking, rutting, and surface condition metrics. Additionally, ODOT continues to sponsor accelerated testing at the NCAT Test Track to validate the field performance of BMD mixtures under controlled conditions. Key conclusions include the selection of IDEAL-CT for statewide use, the importance of determining adequate design aging and production reheating protocols for consistent IDEAL-CT results, and the demonstrated success of collaborative implementation strategies involving both public and private stakeholders. Recommendations for future work include refining CT-Index thresholds based on field performance, developing a framework for RAP management and rejuvenator use, expanding field testing infrastructure, and evaluating the feasibility of performance-based specifications such as percent-within-limits (PWL) pay factors. This work provides a replicable model for transportation agencies seeking to modernize asphalt mix design through performance-based specifications, collaborative implementation strategies, and data-driven decision-making.