Development of Improved Guidelines and Designs for Thin BCOA: Summary, Conclusions, and Recommendations

This report summarizes the investigations undertaken by the University of California Pavement Research Center between 2014 and 2017 to develop recommendations and guidance on the use of thin bonded concrete overlay of asphalt (BCOA) as a rehabilitation alternative for California based on the adoption of, and improvements to, the technology developed in other US states. The main tasks of the project included: 1) laboratory testing of four rapid-strength concrete mixes and a number of concrete-asphalt interfaces, 2) evaluation of the construction of a full-scale test track, 3) monitoring of the structural and hygrothermal responses of six thin BCOA sections to the ambient environment, 4) accelerated pavement testing with the Heavy Vehicle Simulator (HVS) on eleven thin BCOA sections, 5) finite element method modeling, and 6) development of a set of recommendations for the design and construction of thin BCOA pilot projects in California. Based on this testing and analysis, it was possible to obtain a better understanding of the mechanics of the structure of thin BCOA and of the roles of the different factors that determine thin BCOA performance. Overall, the performance of the thin BCOA sections in the HVS testing far exceeded expectations. The 11 sections resisted the predefined HVS loading without cracking. In five of the sections, that loading was equivalent to 6 million equivalent single axle loads (ESALs) and included load levels more than twice the legal limit in California, channelized traffic at the edge of the slabs, and a continuous water supply that simulated flooded conditions. The main conclusion from this research project is that a well-designed, well-built 6×6 thin bonded concrete overlay section placed on top of an asphalt base that is in fair to good condition can potentially provide 20 years of good serviceability on most of California’s non-interstate roadways. Eight individual reports prepared for the project provide a complete description of the work carried out, and include detailed conclusions about each phase. This report includes a summary of those conclusions and a set of recommendations for the design of thin BCOA that considers California traffic, climate and materials conditions, and construction work zone practices.