Elucidating the effects of metakaolin-based geopolymer filler on the performance of styrene-butadiene-styrene modified asphalt: Microstructural insights and mechanistic analysis

This study aims to elucidate the effects of metakaolin-based geopolymer (Mk-Geo) filler on the performance of styrene-butadiene-styrene (SBS) modified asphalt and its underlying mechanisms. Mk-Geo asphalt mastics with varying filler-asphalt ratios (F/A = 0.2～1.4) were prepared, and their microstructural properties and physicochemical interactions were characterized using Fourier-transform infrared spectroscopy, thermogravimetric analysis, Brunauer-Emmett-Teller surface area analysis, and X-ray diffraction. The results revealed that Mk-Geo exhibits a multilayer mesoporous plate-like structure, which significantly influences its interaction with asphalt. Dynamic shear rheometer tests demonstrated that Mk-Geo enhances the high-temperature deformation resistance (indicated by an increase in the rutting factor G*/sinδ) and permanent deformation resistance, while also reducing temperature sensitivity. At F/A = 0.8, Mk-Geo promotes SBS phase swelling through surface adsorption, thereby improving the integrity of the three-dimensional network structure. As the F/A increases, the adsorption capacity of asphalt by the mesoporous structure increases, with a characteristic absorption peak of CaCO₃ crystalline phase appearing at F/A = 1.4. However, High F/A negatively affects the fatigue performance of asphalt mastic, and premature fatigue damage occurs within the asphalt mastic at high strain levels and high F/A, leading to a reduction in fatigue life. In summary, the Mk-Geo can be applied not only as an adsorbent or modifier in asphalt materials, but also as a filler in asphalt mixtures, and the optimal F/A of 1.2 was obtained by ANOVA and statistical analysis. These findings provide a theoretical foundation for the functional application of geopolymers in asphalt pavement engineering.