Evaluation of chip seal mixture design methods using modified Hamburg wheel tracking test and sweep test

The objective of this study was to identify the most effective chip seal design method and chip sizes by conducting a modified Hamburg wheel tracking test and sweep test. Three chip seal design methods, including Austroads, McLeod, and Vietnam methods, were evaluated to design several chip seal mixtures with varying aggregate sizes (e.g., 12.5, 9.5, 4.75, and 2.36 mm) and binder types. To assess the performance of the chip seal mixtures, aggregate loss and bleeding susceptibility were measured. The sweep test was utilized to determine the amount of aggregate loss caused by the sweeping effect, while the modified Hamburg wheel tracking (HWT) test was developed to estimate the aggregate loss caused by the braking effect using a fixed pneumatic rubber tire. Additionally, a modified Hamburg wheel tracking test with a rolling pneumatic rubber tire was used to assess bleeding susceptibility, and the bleeding area was quantified using an image analysis process. The results indicated that the Austroads design method exhibited the lowest aggregate loss compared to the McLeod and Vietnam methods. Moreover, the consistent findings from both the sweep test and modified HWT test demonstrated the feasibility of using the modified HWT test to simulate aggregate loss caused by the braking effect. The bleeding percentage was found to be affected not only by the binder application rate but also by the aggregate size and the number of layers applied. The Austroads and McLeod chip seal mixtures exhibited an approximately 20 % lower bleeding percentage than that of the Vietnam mixtures. Finally, for a single chip seal, a 9.5 mm chip aggregate was determined to be the optimal size, while for a double chip seal, 4.75 mm and 2.36 mm chips were recommended.