Evaluation of bonding performance and enhancement mechanism of tannin isocyanate modified asphalt

The bonding performance plays a crucial role in the long-term service of asphalt pavement. Tannic acid, as a typical biobased material, contains active functional groups such as catechol, which are expected to improve the bonding performance. Based on this, this study conducts the enhancement of asphalt bonding performance and its underlying mechanism using tannin isocyanate synthesized from tannic acid and isocyanate. Three modified asphalt binders were prepared with tannin isocyanate dosages of 3%, 4%, and 5%. The bonding performance and enhancement mechanism were investigated using pull-off tests and dynamic mechanical analysis, complemented by atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), four-component separation (SARA), and molecular dynamics (MD) simulations. The results show that tannin isocyanate significantly improves the maximum bonding strength, interfacial stiffness, and adhesion work within the investigated temperature range. The average microscale adhesion measured by AFM increases by approximately 3-4 times after modification. FTIR indicates increased hydrogen-bond-related functional groups in both asphaltene and resin fractions, while GPC and SARA reveal an increased proportion of asphaltenes and high-molecular-weight components, suggesting strengthened binder cohesion. MD simulations further demonstrate increased interfacial adhesion work between the modified asphalt and representative mineral surfaces, especially CaO and MgO. Overall, tannin isocyanate improves bonding performance through the combined enhancement of interfacial adhesion and binder cohesion. • The purpose of this study is to utilize tannin isocyanate to enhance the interfacial bonding properties of asphalt and analyze the underlying mechanism. • The interfacial bonding properties of tannin isocyanate modified asphalt were studied using a pull-off test based on a dynamic mechanical analyzer and molecular dynamics simulation. • The changes in the microscopic adhesion of tannin isocyanate-modified asphalt were studied using AFM and FTIR test results. The changes in cohesion were analyzed using GPC and SARA test results.