Enhancement of the interface bonding between asphalt binder and aggregate using polyurethane prepolymer as a chemical modifier

The adhesion between asphalt binder and aggregate is crucial for asphalt mixture performance. Although physical adsorption improvements by using various modifiers have been extensively studied, limited research focuses on introducing chemical bonds at the asphalt-aggregate interface. This study investigates the effects of polyurethane prepolymer (PUP) as a reactive modifier to enhance adhesive properties between asphalt binder and aggregate. Frequency sweep, Fourier Transform Infrared Spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) tests were used to investigate interactions between PUP and aggregate. Boiling and pull-off tests further assessed the adhesive properties of PUP-modified binder (PUMB). Additionally, immersion, Marshall stability and freeze–thaw splitting tests examined the effect of PUP on the moisture susceptibility of the asphalt mixture. Results demonstrated that the isocyanate groups in PUP chemically react with hydroxyl groups at the aggregate surface, forming chemical bonds that enhance adhesive strength between the asphalt binder and aggregate. As a result, the incorporation of PUP significantly improves the moisture damage resistance of the asphalt mixture.