Development of Thin Bonded Concrete Overlay of Asphalt Design Method: Evaluation of Existing Mechanistic-Empirical Design Methods

The California Department of Transportation (Caltrans) is interested in advancing the technology needed to implement thin bonded concrete overlay of asphalt (BCOA) on its road network. Recent accelerated pavement tests showed that thin BCOA exhibited promising results for structural performance and constructability in California’s dry environment when made with the high early-strength concrete mixes typically used by Caltrans. However, to continue moving forward, Caltrans needs to adopt a thin BCOA design method since the current Caltrans Highway Design Manual does not consider this type of pavement. In order to help Caltrans decide how to adopt a thin BCOA design method, this technical memorandum includes an evaluation of two existing mechanistic-empirical methods: BCOA-ME, developed by the University of Pittsburgh, and MEPDG, as implemented in Pavement ME Design versions 2.3 (2016) and later. The evaluation includes a sensitivity analysis that considered the most important factors in thin BCOA performance. The evaluation results show that the BCOA-ME and MEPDG methods are both based on sound mechanistic-empirical principles, but that they currently have technical and practical limitations that render them difficult to use for thin BCOA design in California. Based on the analysis presented in this technical memorandum, it is recommended that additional model development be performed to produce a design method that is more suitable for thin BCOA for the Caltrans road network. If Caltrans chooses this option, it is recommended that the new design method incorporate some models already used in BCOA-ME and MEPDG. Regardless of whether Caltrans decides to adopt an existing design method without changes or to further develop models to produce a more suitable method, the selected method will still need to be calibrated for California-specific materials and construction practices, in particular, the use of high early-strength materials; traffic; and climate conditions, with a focus on the prolonged drying that occurs throughout the state