Pavement ME Evaluation of the NCHRP 1-61 Thin Concrete Overlay on Asphalt Sections

The thin concrete overlay on asphalt (COA) longitudinal cracking model of Pavement ME was calibrated with empirical data from COA sections with half-lane width slabs in Minnesota, Illinois, and Colorado. The NCHRP Project 1-61 has considerably expanded the range of climatic conditions for which reliable performance data are available by adding projects from Iowa, Kansas, and Philadelphia (in addition to Minnesota, Illinois, and Colorado). This technical memorandum assesses Pavement ME predictions based on the longitudinal cracking measured on 13 COA sections with half-lane width slabs evaluated as part of NCHRP Project 1-61. None of the 13 sections had more than 3% of slabs with longitudinal cracking, despite four of them being subjected to relatively high traffic volumes (annual average daily truck traffic over 500 vehicles on the design lane) and having been in service between 9 and 19 years. When design values were adopted for the different input variables, Pavement ME predicted less than 5% longitudinal cracking in 12 of the 13 sections, which agrees with measured cracking. The root mean square error (RMSE) of Pavement ME predictions was 2.4% for the set of 13 sections. The RMSE of the Pavement ME predictions improved to 1.2% when constructed slab thickness measured with ground penetration radar was used instead of the design thickness. However, Pavement ME predictions did not improve when measured values for concrete strength or load transfer efficiency were used rather than design values. The recommendation is that the nationally calibrated COA cracking model, implemented in Pavement ME version 2.5.5 (the current version as of the writing of this technical memorandum), be used for developing the California COA design catalog.