The evaluation of relative effect of moisture in Hamburg wheel tracking test

Abstract

Hamburg wheel tracking (HWT) is prominently used for rutting resistance test. The HWT is a versatile device to determine moisture susceptibility and permanent deformation, which has been widely used in many states and agencies in the United States. However, the standard of the test for the HWT device conducted in water is not related to a primary result of rutting, which is due to repeated traffic loading cycle especially in the dry condition. In this study, the HWT test in different conditions (i.e. dry and wet) was conducted to compare the behavior of hot mix asphalt (HMA) during testing. The objective is to determine the comparison between the dry and wet condition testing in HWT test, and to evaluate relative effect of moisture conditioning in wet HWT on the creep stage. Fitting curve using Francken model was applied to determine the tertiary point of HWT curve. Power law model was used to determine the effect of the moisture conditioning in wet HWT on the creep stage. The moisture damage in the wet HWT test was also verified by the Bitumen Bond Strength (BBS) test. The results indicated that the wet HWT currently specified in the AASHTO 324 can be deployed as a substitute to the dry HWT test in the creep stage (before the stripping inflection point) since the difference in creep slope estimated for both conditions is within the experimental error. The wet HWT results after the creep slope remain useful for detecting the moisture sensitivity with the confirmation by the measured cohesion/adhesion of asphalt mastics from each mixture. The BBS test can also verify the moisture sensitivity occurred in the dry and wet HWT with the creep slope and tertiary/stripping slope well correlated to mastic cohesion change in BBS test.