Establishing variability for hot-mix asphalt construction in Arkansas

The Arkansas quality control/quality assurance (QC/QA) specification for hot-mix asphalt (HMA) construction was initially developed from data and experience gained with the Marshall method of mix design. The implementation of Superpave®, coupled with the initiation of the largest asphalt construction program in the state's history, resulted in questions relating to the suitability of the QC/QA specification. Research was undertaken to revise the existing program or create a new specification. The first step in the effort was to establish typical HMA construction variability in terms of the pay factors used in Arkansas: air voids, voids in the mineral aggregate, binder content, and field density. Six projects were randomly sampled and tested by three operators: the contractor, the agency, and the research team. Six specimens were prepared by each operator at each of four testing times within each project. The results of the testing showed that the six projects bracketed a wide variation in mixture quality as defined by the HMA properties. The testing data were normally distributed, validating a typical assumption regarding construction. Analyses showed that the testing variability among the three operators could be absorbed into the overall variability of test properties instead of being considered a distinct factor. Three levels of HMA quality were identified by the mean and standard deviation of the test data. These quality levels are expected to form the basis for any revision to the existing QC/QA system or for the development of a new QC/QA system for Arkansas HMA construction.