Microstructural Characteristics and Modification Mechanism of Inorganic Fine Particles in Buton Rock Asphalt

The properties of natural inorganic fine particles in Buton rock asphalt (BRA) and the effects of asphalt modification on these particles were analyzed in order to study the role of the natural inorganic fine particles in the process of asphalt mixture modification. First, X-ray diffraction (XRD) patterns and microscopic images of the inorganic fine particles were obtained using X-ray diffraction and scanning electron microscopy (SEM). Secondly, the mineral composition, microscopic characteristics, and mechanism of the formation of the natural inorganic fine particles in BRA were analyzed through the K value method and grayscale image processing. Finally, the effects of the inorganic particles on the performances of mastic and asphalt mixtures were determined using the dynamic shear rheological test (DSR) and mixture performance tests. The results show that the natural inorganic fine particles in BRA contain approximately 85% carbonatite, which is mainly formed from the remains of ancient halobios and partially retained the primary structure. The content of non–carbonate inorganic minerals reaches 15%, of which the proportions of quartz, muscovite, and gypsum are approximately 7:6:1. The surface area of the particles covered by micro-rough structures composed of layered and tabular crystals can reach more than 80%. The preservation of the original microstructural characteristics, recovery, and the enhancement of the organic binder filling state of the microstructure are the main factors responsible for the modification effect of the natural particles. The partial substitution of artificial mineral particles by natural inorganic fine particles can increase the rutting factor of the asphalt mastic, dynamic stability, and freeze-thaw tensile strength by 0.524 kPa, 18.8%, and 5.1% respectively, and the tensile strength ratio can increase to more than 83.5%. The use of natural inorganic fine particles as an aid in compound modifiers improves the performance of the mastic and asphalt mixtures. When the mastic or mixture is modified with natural asphaltene, the natural inorganic fine particles increase the rutting factor of the asphalt mastic, dynamic stability, and freeze-thaw tensile strength by 0.674–0.910 kPa, 21.1%–25.6%, and 3.5%–5.6% respectively, and the tensile strength ratio increases from 85% to more than 90%.