To analyze the effect of polyol on polyurethane (PU)-modified asphalt, three different soft segments of polyurethane were synthesized, and we utilized the reaction of MDI (diphenylmethane diisocyanate) with PU650, PU1000, and PU1400. With respect to molecular weight, the effect of polyol on the performance of modified asphalt was analyzed, and the asphalt was modified by using three different polyurethanes. To analyze the PU samples, the Fourier transform infrared spectroscopy (FTIR) tests and gel permeation chromatography (GPC) tests were selected; by contrast, to analyze the rheological properties and modification mechanism of asphalt, the dynamic rheology test (DSR), low-temperature bending creep test (BBR), multi-stress repetitive creep test (MSCR), FTIR, and differential scanning calorimetry (DSC) were selected. The results indicate that the molecular weight of polyol affects the molecular structure of polyurethane, the distribution of soft and hard segments, the content of soft segments, and the distribution of asphaltene in asphalt; thus, the asphalt modification effect occurs differently. The storage stability and high-temperature stability of the polyurethane-modified asphalts that were synthesized using three different polyols (i.e., polyols that exhibit different molecular weights) did not differ considerably, and the PU1400-modified asphalt exhibited the best low-temperature performance.

Lignin, an abundant and renewable biopolymer, holds significant potential for asphalt modification owing to its unique aromatic structure and reactive functional groups. This review summarizes the main lignin preparation routes and key physicochemical attributes and assesses its applicability for enhancing asphalt performance. The physical incorporation of lignin strengthens the asphalt matrix, improving its viscoelastic properties and resistance to oxidative degradation. These enhancements are mainly attributed to the cross-linking effect of lignin’s polymer chains and the antioxidant capacity of its phenolic hydroxyl groups, which act as free-radical scavengers. At the mixture level, lignin-modified asphalt (LMA) exhibits improved aggregate bonding, leading to enhanced dynamic stability, fatigue resistance, and moisture resilience. Nevertheless, excessive lignin content can have a negative impact on low-temperature ductility and fatigue resistance at intermediate temperatures. This necessitates careful dosage optimization or composite modification with softeners or flexible fibers. Mechanistically, lignin disperses within the asphalt, where its polar groups adsorb onto lighter components to boost high-temperature performance, while its strong interaction with asphaltenes alleviates water-induced damage. Furthermore, life cycle assessment (LCA) studies indicate that lignin integration can substantially reduce or even offset greenhouse gas emissions through bio-based carbon storage. However, the magnitude of the benefit is highly sensitive to lignin production routes, allocation rules, and recycling scenarios. Although the laboratory research results are encouraging, there is a lack of large-scale road tests on LMA. There is also a lack of systematic research on the specific mechanism of how it interacts with asphalt components and changes the asphalt structure at the molecular level. In the future, long-term service-road engineering tests can be designed and implemented to verify the comprehensive performance of LMA under different climates and traffic grades. By using molecular dynamics simulation technology, a complex molecular model containing the four major components of asphalt and lignin can be constructed to study their interaction mechanism at the microscopic level.

To prepare high-performance asphalt cold replacement liquids, a composite modification preparation process was used to synthesize a styrene–butadiene–styrene (SBS) block copolymer, styrene–butadiene–rubber (SBR) copolymer, and polyphosphate acid (PPA), erucamide/diesel/acrylic ester as surfactants/diluents/reinforcing agent respectively. These six were blended to prepare an asphalt cold replenishment liquid (ACRL), and its modification effect on base asphalt was studied using base asphalt as the control group. A comparative study was conducted on the high- and low-temperature rheological properties and microstructure. The modification mechanisms of high-temperature asphalt cold replenishment liquid (H-ACRL) and low-temperature asphalt cold replenishment liquid (L-ACRL) were studied through dynamic shear rheometry, bending beam rheometry, Fourier-transform infrared spectroscopy, fluorescence microscopy, and atomic force microscopy. The results showed that the optimal dosages of PPA/SBS/SBR in H-ACRL and L-ACRL were (1.2%/5%/3%) and (0.9%/4%/4%), respectively. Within the optimal dosage range, the particles in the cold replenishment fluid were uniformly dispersed in the asphalt to form a dense and continuous network. No new functional groups were generated during the preparation of H-ACRL and L-ACRL, showing that the modifiers (surfactants/diluents/reinforcing agent) were only physically blended with the asphalt.

To optimize the dry mixing preparation process for permeable asphalt mixtures and elucidate the microscopic mechanism of high-viscosity modifiers, this study employed Response Surface Methodology (RSM). Independent variables, including mixing temperature, dry mixing time, and wet mixing time, were selected, with Marshall stability, −10 °C splitting tensile strength, and residual stability as response indicators. The significance and fitting accuracy of the model were evaluated through Analysis of Variance and residual diagnosis. Additionally, the morphological evolution, spatial distribution, and chemical interactions of the modifier were characterized using scanning electron microscopy (SEM), fluorescence microscopy (FM), and Fourier Transform Infrared Spectroscopy (FTIR). The results revealed distinct differences in factor effects: mixing temperature most strongly influenced high-temperature performance, while wet-mixing time primarily governed low-temperature performance and water stability. Furthermore, significant interactions were observed among the variables. Multi-objective optimization determined the optimal process parameters to be a mixing temperature of 182 °C, dry mixing time of 180 s, and wet mixing time of 102 s. Experimental validation confirmed that the relative error between predicted and actual values was within 5%. Microscopic characterization revealed that under the dry mixing process, the modifier undergoes four stages: rapid melting, viscous flow, permeation diffusion, and swelling development. An appropriate mixing temperature combined with sufficient dry and wet mixing times promotes the formation of a uniform, dense spatial network structure of the modifier within the asphalt. This study validated the reliability of RSM in process optimization, providing theoretical foundations and key technical parameters for the green and efficient production of high-performance permeable asphalt mixtures.