Use of the Hamburg Wheel-Tracking Test to Characterize Asphalt Mixtures in Cool Weather Regions

The Hamburg wheel-tracking test (HWTT) has shown promise to predict permanent deformation resistance and moisture damage potential of asphalt mixtures. Several state agencies have implemented the test as a mixture evaluation and design tool. One aspect of the test that remains a topic of research is the testing temperature. Many studies and specifications use 50°C for all testing, but some use a test temperature that depends on the base asphalt used in the mixture. Concern exists about the use of 50°C as the sole test temperature in cooler weather regions, such as Wisconsin, because the asphalts used in such regions tend to be relatively soft (high temperature grades of PG 58 and below). This paper presents findings in support of an effort to apply the HWTT to mixtures in cold climates with the use of three test temperatures and several mixture design variables. The paper presents the effects of the mixture design traffic level, the PG of the binder, and the binder modification level on the deformation resistance, creep slope, stripping slope, and stripping inflection point (SIP). The HWTT was found to be sensitive to the factors evaluated in this study. On the basis of statistical analysis of the test data, logical trends were observed. The testing temperature was found to affect not only the response variables but also the level of significance of controlled factors. The effectiveness of the SIP to characterize the moisture sensitivity of mixtures requires more research to validate the effect of moisture damage on HWTT results.