Micromechanics approach to calculate the adsorbed asphalt film thickness on mineral fillers and evaluate physiochemical interactions

Investigations of the physicochemical interactions occurring at asphalt–mineral filler interfaces are important in understanding the mechanisms that govern the mechanical attributes of asphalt mixtures. The measurement of the adsorbed asphalt film thickness (AAFT) provides valuable insights into the underlying physicochemical interactions. However, direct measurement of AAFTs through laboratory tests poses considerable challenges. This study describes AAFT calculation methods based on the N-phase model and Christensen-Lo model. The AAFTs of different types of asphalt mastic were calculated by conducting dynamic shear rheology (DSR) tests. To ascertain the physicochemical mechanisms governing interactions between the asphalt and mineral fillers, fourier transform infrared (FTIR), Brunner−Emmet−Teller (BET), scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies were carried out. The findings revealed that the AAFT was related to the testing temperature, frequency, filler content, and type. The AAFTs for asphalt mastics with different filler types decreased in the order (from thick to thin) of coal gangue filler, limestone filler, and fly ash. The external specific surface areas and chemical compositions of the mineral fillers emerged as the primary factors influencing their physicochemical interactions with the asphalt. The coal gangue asphalt mastic exhibited a smaller and denser AFM bee structure, which was attributed to the physicochemical interactions. The findings of this research contribute to the selection of mineral fillers and filler/binder ratios that can be utilised for optimising the design of asphalt mixtures comprising different types of fillers.