To explore the interactions and mechanisms of Thermoplastic polyurethane (TPU)-modified asphalt with different kinds of mineral fillers, a micro-mechanical model for TPU-modified asphalt mastic was established, which considered the interaction between asphalt and mineral powder to effectively analyze the internal mechanisms affecting the rheological properties of TPU-modified asphalt mastic. In this study, according to the micro-mechanics of composites’ principles, the dynamic shear modulus (|G^*|) of asphalt mastic with different mass ratios of filler/asphalt (F/A) was calculated by the homogenize morphologically representative pattern (H-MRP) model. The key ratio of F/A, which is close to the test result, can be determined, and a four-phase H-MRP model of the TPU modified asphalt mastic was established after considering the structure of asphalt layer thickness. The results were interpreted based on the known reactions of TPU with asphalt model compounds. The |G^*| of TPU-modified asphalt mastic was predicted by using this model. Furthermore, the effects of the complex shear modulus, Poisson’s ratio of TPU-modified asphalt, Poisson’s ratio, particle size of mineral powder, and thickness of the structural asphalt layer in the |G^*| of TPU-modified asphalt mastic were analyzed in the whole-model construction, as well as the internal mechanism of the |G^*| of TPU modified asphalt mastic. In addition, can also be found the predicted value of |G^*| calculated by the four-phase H-MRP model is close to the experimental value after choosing a structural asphalt layer of appropriate thickness.

In actual service, asphalt pavement is subjected to freeze–thaw cycles and ultraviolet radiation (UV) over the long term, which can easily lead to mixture aging, enhanced brittleness, and structural damage, thereby reducing pavement durability. This study focuses on the influence of freeze–thaw cycles and ultraviolet aging on the performance of recycled asphalt mixtures. Systematic indoor road performance tests were carried out, and a fatigue prediction model was established to explore the comprehensive effects of recycled asphalt pavement (RAP) content, environmental action (ultraviolet radiation + freeze–thaw cycle), and other factors on the performance of recycled asphalt mixtures. The results show that the high-temperature stability of recycled asphalt mixtures decreases with the increase in environmental action days, while higher RAP content contributes to better high-temperature stability. The higher the proportion of old materials, the more significant the environmental impact on the mixture; both the flexural tensile strain and flexural tensile strength decrease with the increase in environmental action time. When the RAP content increased from 30% to 50%, the bending strain continued to decline. With the extension of environmental action days, the decrease in the immersion Marshall residual stability and the freeze–thaw splitting strength became more pronounced. Although the increase in RAP content can improve the forming stability, the residual stability decreases, and the freeze–thaw splitting strength is lower than that before the freeze–thaw. Based on the fatigue test results, a fatigue life prediction model with RAP content and freeze–thaw cycles as independent variables was constructed using the multiple nonlinear regression method. Verification shows that the established prediction model is basically consistent with the change trend of the test data. The research results provide a theoretical basis and optimization strategy for the performance improvement and engineering application of recycled asphalt materials.

Asphalt mastic serves as a critical binding material in hot mix asphalt mixtures, significantly influencing the performance and durability of asphalt pavements. The interaction between asphalt and mineral fillers directly affects the binding properties of the mastic. In this study, the adsorbed asphalt film thickness was used as an indicator to evaluate the interaction between asphalt and mineral fillers. A micromechanical approach was proposed to calculate this thickness, and the results were compared using the Hashin model, the Mori–Tanaka model, and the generalized self-consistent model. The results demonstrate that the adsorbed asphalt film thickness, as determined using the micromechanical approach, ranged from 0.01 to 0.37 µm. The Hashin model was found to provide the most accurate characterization of the interaction between the asphalt and the mineral fillers. The order of adsorbed asphalt film thickness was as follows: coal gangue asphalt mastic > limestone asphalt mastic > fly ash asphalt mastic. Higher concentrations of acidic SiO₂ in the mineral fillers resulted in a weaker interaction between the asphalt and the fillers. When the temperature was below the softening point of the asphalt, the interaction strength decreased as frequency increased. Conversely, when the temperature exceeded the softening point, the interaction strength increased with frequency. The effect of temperature on the interaction capability was further influenced by the characteristics of the mineral fillers. The micromechanical-based method proposed in this study eliminates the dependency of the evaluation indicator on the volume fraction of mineral fillers, thereby providing a more accurate characterization of the interaction between asphalt and fillers. This approach provides a theoretical foundation to guide the design of asphalt mixtures.

An asphalt modifier dry-process direct-cast oil-rich high-viscosity high-elasticity (OR-HV-HE) was developed to address the climatic characteristics of seasonal freezing zones. The chemical composition of the OR-HV-HE modifier was optimized through orthogonal testing. Advanced characterization techniques, including thermogravimetric analysis (TG), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR), were employed to systematically analyze the comprehensive thermal properties, microstructure, and chemical characteristics of the OR-HV-HE asphalt. Test results revealed a linear inverse relationship between the melt index and the OR-HV-HE asphalt grafting rate. The addition of the OR-HV-HE modifier led to the generation of new chemical bonds, and microscopic mechanism analysis illustrated the formation of a cross-linking network structure between the OR-HV-HE and asphalt, in which the cross-linking network structure could enhance the high and low-temperature performance of asphalt. Road performance verification results demonstrated that when compared with the traditional SBS-modified asphalt mixture, the OR-HV-HE modified asphalt mixture exhibited significantly superior road performance indices: the high-temperature dynamic stability was increased by 468% and the low-temperature damage strain was increased by 47.5%, and the residual stability reached 99%.