Raveling performance of conventional and rubberized chip seal under field and laboratory traffic loading

Raveling, or the loss of surface aggregate, is a major concern in chip seal pavement. Previous studies have used the Standard Sweep, Vialit, and Pennsylvania tests to evaluate raveling, but these tests do not replicate the stresses of rolling vehicle tires on chip seal and have produced inconsistent results. Additionally, these tests mainly evaluate early-stage raveling due to their short curing time. In this study, a small-wheel traffic simulation device (SWTS) was used to apply similar stresses as rolling vehicle tires and produce comparable raveling results. This was confirmed through a 13-month field observation of chip seal, where the laboratory and field data were compared and correlated. Both conventional (mineral aggregate) and eco-friendly rubberized chip seal with 25%, 50%, and 100% crumb rubber as aggregate were tested in the laboratory and field. The effects of different aggregate types, binder application rates, and crumb rubber contents were studied. The results showed that each wheel application by SWTS is equivalent to 2.5 to 3 passenger car passes in the field. It was also found that the majority of macrotexture loss occurred in the first 50,000 passenger car equivalent load. Up to 50% replacement of mineral aggregate with crumb rubber did not significantly affect the raveling resistance but using more than 50% rubber impaired the raveling resistance. Using crumb rubber instead of mineral aggregate also significantly reduced tire wear and microplastic emissions from vehicle tires. Moreover, it was found that Pennsylvania and Vialit tests may not be suitable for assessing aggregate retention under traffic load.