Research on the Water Stability of Compound Modified Asphalt Mixtures of Bridge Expansion Joints

In this paper, two types of polymer modifiers and an asphalt binder were used to prepare compound modified asphalt binders sealant for bridge expansion joints. The fine aggregates of a single gradation along with three corresponding types of asphalt-aggregate ratios were selected to prepare compound modified asphalt mixtures for the surface asphalt layer of the bridge expansion joint. Similarly, the coarse aggregates of a single gradation along with another three types of asphalt-aggregate ratios were selected to prepare compound modified asphalt mixtures for the base asphalt layer of the bridge expansion joint. This study evaluated the water stability of the mixtures for un-aged, and short-term and long-term oven aged conditions using the immersion Marshall test and the Freeze-thaw Split test. Additionally, the adhesion between the aggregate and the compound modified asphalt was evaluated before and after oven-aging. The water stability of the six compound modified asphalt mixtures for road surface and substrate were compared. The test results indicate that, before and after aging, the best compound modified asphalt mixtures for surface and base asphalt layers exhibited an adhesion index of 5 and retained stability and freeze-thaw strength ratios (TSR) above 90%. Furthermore, TSR of the un-aged asphalt mixtures was the highest when compared to the TSR at the other aging conditions. After short-term aging, a decrease in TSR was generally observed, however a slight increase in TSR was observed after long-term aging.