Fischer–Tropsch (FT) wax is widely used as an organic warm-mix asphalt (WMA) additive, lowering binder viscosity during construction while improving high-temperature deformation resistance in service; however, the comparative responses of SBS-modified asphalt to different FT wax grades remain insufficiently understood. Sasobit and three FT waxes with different carbon-chain ranges (FT 80, FT 90, FT 100) were incorporated into SBS-modified asphalt at about 7.0 wt%, and their effects on macroscopic performance, rheology, molecular packing, and diffusion were evaluated using physical-property tests, rotational viscosity, dynamic shear rheometer (DSR) testing, and molecular dynamics (MD) simulation. In the MD analysis, the wax additives were represented by linear alkane molecules with different chain lengths, and the systems were subjected to structural optimization, annealing, and NPT equilibration using the COMPASS III force field before the molecular descriptors were evaluated. The experimental results showed that all four additives produced a trade-off between increased high-temperature stiffness and reduced low-temperature ductility. Sasobit gave the strongest viscosity reduction (>70% above 165 °C), while FT 90 and FT 100 showed more stable, predictable viscosity–temperature behavior favorable for a wider construction window. DSR results showed higher complex modulus and lower phase angle for all modified binders at low frequencies, suggesting an increased elastic contribution and greater resistance to deformation under the tested rheological conditions; FT 80 produced the greatest stiffening but also the largest free volume and loosest molecular packing, whereas FT 100 increased cohesive energy density and reduced free volume, reflecting denser packing and stronger intermolecular cohesion. MD simulations revealed that FT wax enhanced short-time local molecular mobility and segment diffusion in its molten state (explaining the warm-mix viscosity reduction), whereas macroscopic stiffening and ductility loss at ambient temperatures were dictated by wax microcrystallization and physical network constraints that restricted long-range chain relaxation. By comparing three FT wax grades and Sasobit under the same experimental dosage and testing framework, this study provides a controlled assessment of the relationships among wax-grade characteristics, binder-scale rheological responses, and MD-derived molecular descriptors.

Rural road construction in the loess region of Gansu Province is constrained by aggregate shortage, high material transportation costs, and the limited early performance of cement-stabilized soil. In this study, KDJ-II stabilizer and cement were used to prepare KDJ-II–cement composite-stabilized soil for potential use as a base-course material. Compared with cement-stabilized soil, the addition of 0.02% KDJ-II increased the 7-day unconfined compressive strength, splitting tensile strength, and resilient modulus by 16.7%, 17.6%, and 12.1%, respectively. Leaching-based ion concentration analysis, XRD, FTIR, and SEM were used to interpret the early strength development mechanism. The results suggest that KDJ-II influenced the leachable ion release and retention behavior of the cement-stabilized soil and helped form a sulfate-rich, alkaline, and soluble-silica-bearing reaction environment under the tested conditions. This environment may favor the development of sulfate-bearing hydration products, the activation of primary aluminosilicate minerals, and the formation of C–S–H-like gels. The coupled variations in leachable Ca²⁺, SO₄²⁻, and Na⁺, together with the increase in calcite, decrease in albite, broadening of the absorption band at approximately 1018 cm⁻¹, and the SEM-observed needle/fibrous products, flocculent gels, and reduced visible pores, collectively support the interpretation that KDJ-II promotes particle cementation, pore filling, and microstructural densification. Overall, this study indicates that, under the selected mixture proportion and curing condition, KDJ-II can improve the early strength and stiffness of cement-stabilized loess by modifying the early reaction environment and promoting the coordinated development of hydration-related products and a denser microstructure.