Fly ash is one of the industrial waste residues with significant emissions in China, and its rational utilization has important economic significance and environmental value. Due to the similarity in properties between fly ash and limestone mineral powder, it is possible to replace the mineral powder filler in asphalt concrete with fly ash. This article explored the feasibility of replacing the mineral powder with fly ash in an asphalt mixture through the study of fly-ash-modified asphalt mastic. Firstly, the microstructures and elemental compositions of fly ash and mineral powder were studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. Then, the rheological properties of asphalt mastics with different fillers were studied using dynamic shear rheological (DSR) tests. The results show that when the stress level was 3.2 kPa, the change in the J_nr value was different from that at 0.1 kPa, indicating that after increasing the stress level, the J_nr of fly ash asphalt mastic was smaller, and fly ash can improve the high-temperature creep performance of asphalt mastic. Replacing mineral powder with fly ash can improve the high-temperature rheological properties of asphalt mastic, but this damages the elastic and crack resistance properties of the asphalt mastic. In practical applications, partial substitution of mineral powder can be considered for the preparation of an asphalt mixture.

CaCO₃ whiskers, as a micron-level inorganic fiber material, can enhance and toughen composite materials. In order to study the technical feasibility of CaCO₃ whisker-modified asphalt, two types of silane coupling agent (SCA), KH-550 and KH-570, were applied to treat the surface of CaCO₃ whiskers, and the treatment effects of the original and treated whiskers were characterized by scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS) and contact angle test. Meanwhile, models of CaCO₃ whiskers, SCA, and asphalt molecules were established by Material Studio (MS, 2020 version) software, and the adhesion mechanism between the CaCO₃ whiskers-and-asphalt interface was predicted. The results of microscopic characterization experiments indicate that the surface of the whiskers treated with SCA became rougher. Compared with the original whiskers, the contact angle between the treated whisker surface and water increased from 50° to 92.2° and 103.4°, and the surface of whiskers changed from hydrophilic to hydrophobic. The results of molecular dynamics simulation analysis show that the adhesion performance between the CaCO₃ whisker surface and asphalt increased from 100.1 mJ/m² to 112.5 mJ/m² and 126.6 mJ/m² after modification with SCA, and the increase in adhesion energy of KH550 is greater than that of KH570. The above research results indicate that the micro-characterization results were consistent with the molecular dynamics simulation results; that is, after treatment with SCA, the adhesion energy between the whiskers and asphalt was increased to varying degrees. The research method in this article combines micro-characterization with molecular dynamics simulation, which has a certain degree of innovation.