Review of Percent Within Limits for Dense Graded HMA
Civil and Environmental Engineering
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Nevada Department of Transportation (NDOT) has asked the University of Nevada, Reno to research and develop a Percent With Limits program. They find it difficult to enforce demerits when pavement sections are measured to be out of tolerance. For example, if a pavement section is found to have poor compaction or unacceptable asphalt binder content, they are supposed to suspend the construction. However, they may allow construction to proceed if those same sections pass other parameters. This ambiguity has caused confusion among the contractors and it may have allowed inadequate pavement sections be left in place without penalty. In addition, NDOT currently evaluates pavement sections based on single test points or an average of the test points. There is no consideration for the variability or consistency of the measured parameters, as long as they are within the upper and lower specification limits. A literature review covering 11 states was performed in order to present to NDOT how other states utilize PWL. They include Arizona, California, Colorado, Idaho, Kansas, Michigan, New Mexico, New York State, Utah, Vermont, and Washington State. These states employ the PWL methodology and details of their methods were evaluated. This report provides information such as lot and sublot sizes, parameters used for testing, frequency of testing, upper and lower specification limits, pay factor calculations, and how the pay adjustment was conducted. Pavement performance relies heavily on how well it was constructed. By utilizing a PWL system, contractors are provided an incentive to produce higher quality roads by building them closer to the target values and with less variability. PWL allows the agency to estimate the quality of the constructed pavement and issue bonuses or penalties based on the justified results of the PWL analysis.