Performance Evaluation of Thin Wearing Courses Through Scaled Accelerated Trafficking

The primary objective of this study was to evaluate the permanent deformation (rutting) and fatigue performance of several thin asphalt concrete wearing courses using a scaled-down accelerated pavement testing device. The accelerated testing was conducted using a model mobile load simulator (MMLS3). Field testing with the MMLS3 was conducted on a 4.75-mm nominal maximum aggregate size dense-graded mixture installed at the Turner-Fairbank Highway Research Center. This mixture (designated SM-4.75), two other conventional dense-graded mixtures, and a thin gap-graded mixture were also used to prepare specimens for laboratory rutting tests using the MMLS3. Test results from more than 100,000 wheel load applications of the MMLS3 showed that the thin wearing courses underwent various degrees of permanent deformation depending on their compacted air void content. According to the protocol guidelines developed for the evaluation of permanent deformation and moisture damage when using the MMLS3, most of the mixtures performed well. One exception was a coarser dense-graded material with a high amount of recycled asphalt pavement. No indication of fatigue cracking or other distress was observed for any mixture during or after testing. The study supports use of the SM-4.75 mixture on low- to medium-traffic roadways and for maintenance and/or preservation applications. It further recommends that the Virginia Department of Transportation apply the methods demonstrated through this research to assess better the stability of experimental wearing course mixtures in advance of wider spread field applications.