Development of a testing temperature to be used with the Hamburg Wheel Tracking Device on asphalt mixtures that utilize performance grade binders

The Hamburg Wheel Tracking Device (HWTD) is used in the laboratory to evaluate an asphalt mixture’s potential for failure in the field. This test observes damage due to rutting and moisture susceptibility on a prepared asphalt sample. The test is generally run at 50° C regardless of the type of mix or the grade of asphalt binder used in the mixture. This work evaluates the effect that test temperature has on HWTD test results, and their relation to mixture performance. Slabs were prepared using a linear kneading compactor and tested in the HWTD at multiple temperatures. Three binder grades were evaluated, a PG 58-28 unmodified, a PG 70-28 modified with polymers and polyphosphoric acid (PPA), and a PG 64-28 obtained by blending the PG 70 and the PG 58. The binders were obtained from different sources common to the state of Utah resulting in a total of six binder combinations. Based on tests performed at different temperatures, it was determined that failure caused by moisture damage in the HWTD is a function of the presence of water, the wheel load, the chemistry, and the water bath (testing) temperature. The data show that there is a Critical Stripping Temperature (CST) that provides the energy, in the form of heat, which reduces the stiffness and de-bonds the binder from the aggregate. Since modified binders are intended for use in environments where the pavement temperature reaches values well above 50° C, it was concluded that a higher testing temperature is needed. Based on the data collected, testing at 50° C is suggested for mixtures intended to iv be used in environments where a PG 64-XX binder is recommended. Mixtures intended to be used in an environment where a PG 70 – XX binder is recommended should be tested in the Hamburg Wheel Tracking Device at a higher temperature of 54° C. Mixture prepared with a PG 58-XX binder will most likely fail the test at 50° C so a lower temperature of 46° C is recommended if warranted by the expected environment. It is important that high performance grade (PG) hot-mix asphalt (HMA) to be used in hotter than average environments be tested at hotter temperatures. This research shows that even under the “worst case scenario,” every sample of PG 70-28 prepared and tested, passed, and would be laid on Utah roads. Testing a PG 70-28 at 50° C only insures that the bond between the asphalt and binder in the high PG HMA is as strong a bond as is found in a PG 64-28. This work evaluates the effect that test temperature has on Hamburg Wheel Tracking Device test results, and their relation to mixture performance. Three binder grades were evaluated, a PG 58-28 unmodified, a PG 70-28 modified with polymers and polyphosphoric acid (PPA), and a PG 64-28 obtained by blending the PG 70 and the PG 58. The data show that there is a Critical Stripping Temperature (CST) that provides the energy, in the form of heat, which reduces the stiffness and de-bonds the binder from the aggregate. Since modified binders are intended for use in environments where the pavement temperature reaches values well above 50° C, it was concluded that a temperature higher than 50° C is needed to accurately evaluate a hot mix asphalt's moisture susceptibility. TABLE OF CONTENTS ABSTRACT iii LIST OF TABLES vii LIST OF FIGURES viii LIST OF ABBREVIATIONS ix ACKNOWLEDGEMENTS x LITERATURE REVIEW