Abstract
The Hamburg wheel-tracking test (HWTT) is commonly used to evaluate the rutting resistance and moisture susceptibility of asphalt mixtures. Over the years, different test parameters have been proposed, including the traditional ones specified in AASHTO T 324 and several alternatives developed by asphalt researchers. This study was undertaken to refine the HWTT method toward enhancing its implementation as part of balanced mix design specifications for asphalt mixtures. A HWTT database was developed including test results of over 70 mixtures with a wide range of mixture components and production parameters. Data analyses were conducted to examine the relationships among various HWTT parameters, determine their correlations to field performance data, and estimate the within-laboratory repeatability of the test results. Two alternative rutting parameters, rutting resistance index (RRI) and corrected rut depth (CRD), were found to be advantageous over the traditional parameters of total rut depth (TRD) and creep slope (CS). RRI allows for direct comparison of results with different termination points, and CRD isolates the rut depth resulting from permanent deformation from that caused by stripping. Among all the rutting parameters, RRI had the best correlation to field rut depth, followed by CS, CRD, and TRD. Receiver operating characteristic analysis was conducted to determine the correspondence between HWTT results and pavement field performance related to moisture susceptibility. The analysis identified 9,000 passes as the best criterion for stripping inflection point and 2,000 passes for the alternative moisture susceptibility parameter, stripping number. Finally, the within-laboratory repeatability of HWTT rut depth measurements was determined.
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