Predicting Field Performance on the NCAT Pavement Test Track
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An experimental facility has been constructed near the campus of Auburn University for the purpose of conducting research to extend the life of flexible pavements. Experimental sections on the 2.8 kilometer Pavement Test Track are cooperatively funded by external sponsors, most commonly state departments of transportation (DOTs), with operation and research managed by the National Center for Asphalt Technology (NCAT). Forty-six different flexible pavements were initially installed at the facility in 2000, each at a length of 61 meters. Materials and methods unique to section sponsors were imported during construction to maximize the applicability of results for the individual sponsors. A design lifetime of truck traffic was applied in an accelerated manner over a two-year period of time, with field performance documented weekly. Sponsors typically planned to compare the performance of two or more sections constructed with different materials and/or methods to obtain information that could be used to build pavements with a better life cycle to cost ratio. In addition to assessing alternatives for sponsors, NCAT was responsible for guiding the overall effort in a direction that would address policy issues for the highway industry as a whole. Specifically, laboratory methods that have the potential to predict rutting when used during construction are compared herein to a detailed record of field performance as a function of traffic over a range of temperatures for every experimental mix. This new method of characterizing traffic is referred to as “load-temperature spectra.” Regression methods are used to generate a distinct prediction model for each laboratory test based on weekly changes in rutting, and statistical methods are utilized to evaluate the success of each method. The suitability of testing during gyratory compaction, simulative testing, and fundamental testing in assessing the rutting performance of research mixes is evaluated with recommendations made for future practice.