Development, Implementation, and Verification of Performance Based Specifications for High-Performance Thin-Lift Overlay Mixtures

State DOT agencies from the Northeast Pavement Preservation Partnership (NEPPP) as well as the Pennsylvania Asphalt Pavement Association (PAPA) were involved in the development of a pilot specification for high performance thin overlay (HiPO) mixtures. The pilot specification addressed surface preparation, material properties (binder, aggregate, tack coat), mixture design requirements, Reclaimed Asphalt Pavement (RAP) testing requirements, performance criteria for the asphalt binder in terms of thermal cracking, and mixture performance criteria in terms of reflective cracking, thermal cracking, fatigue cracking, and rutting. The National Center for Pavement Preservation (NCPP) published and posted the pilot specification on the AASHTO Transportation System Preservation Technical Services Program (AASHTO TSP2) web site. From the posting of the pilot specification, multiple state agencies expressed interest in utilizing the pilot specification for demonstration paving projects. In 2011, three state agencies (Minnesota, New Hampshire, and Vermont) placed demonstration projects of the HiPO mixture incorporating up to 25% RAP. The focus of this study was to assist the three state DOT agencies in evaluating the performance of the plant produced mixtures from the field projects in the laboratory based on performance criterion listed in the pilot specification. Based on the evaluation of the mixtures and field observations, several recommendations are provided to refine the pilot specification. In particular, it is recommended to put more emphasis on the testing of the RAP materials as it has showed a significant impact on the performance of the mixtures. Additionally, several criteria will be monitored in order to correlate with field performance.