Presently, there is a significant focus on the investigation and advancement of polymer-modified asphalt that is both high-performing and environmentally sustainable. This study thoroughly examined the performance and modification mechanism of gutta-percha (GP) as a novel asphalt modifier. The investigation was conducted using a combination of macro- and microscopic testing, as well as molecular dynamics simulations. This work primarily examined the compatibility of GP with asphalt molecular modeling. This paper used molecular dynamics to identify the most suitable mixing temperature. Next, the gray correlation theory was used to discuss the most effective method for preparing gutta-percha-modified asphalt (GPMA). The macro-rheological tests and microscopic performance analysis provided a full understanding of the impact of GP on asphalt properties and the process of alteration. The findings indicate that eucommia ulmoides gum (EUG) exhibits good compatibility with asphalt, while sulfur-vulcanized eucommia ulmoides gum (SEUG) does not demonstrate compatibility with asphalt. Both EUG and SEUG enhance the thermal stability and resistance to deformation of asphalt at high temperatures, with SEUG having a particularly notable effect. However, both additives do not improve the resistance of asphalt to cracking at low temperatures. The manufacturing method for EUG-modified asphalt (EUGMA) involves physical mixing, whereas sulfur-vulcanized eucommia ulmoides gum-modified asphalt (SEUGMA) involves physical mixing together with certain chemical processes. This research establishes a theoretical foundation for the advancement of GP as a novel environmentally friendly and highly effective asphalt modification.

To further advance the recycling of pavement waste, the secondary-aging and multiple-rejuvenation processes of bitumen are first systematically reviewed. Beginning with primary-aging mechanisms, rejuvenator classification and physicochemical properties are summarized to aid elucidation of primary rejuvenation. Secondary-aging evolution of technical and physicochemical properties of rejuvenated bitumen (RB) is critically analyzed. The aging resistance of virgin bitumen and RB is quantitatively compared via extensive literature data. The background and progress of multiple rejuvenation cycles are also outlined. The existing literature shows that identical aging modes can induce distinct component variations, while degradation patterns remain consistent across modes. Among petroleum-based rejuvenators, those with aromatic content exceeding 60% are widely used, and the polar carboxyl groups of tall oil account for their high efficacy. RB aging resistance strongly correlates with both rejuvenator type and dosage. Most RB outperforms virgin bitumen in aging resistance, and post-aging variation amplitudes of softening point and high-temperature failure temperature are approximately 20% for both, while those of penetration and viscosity range from 60% to 120%. Multiple aging–rejuvenation trends resemble those of primary cycles, with progressive macro- and micro-property deterioration as cycles increase. Future work includes developing high-performance bitumen from aged feedstock, establishing molecular screening systems for fatty acid bio-oil rejuvenators, and advancing multiple rejuvenation via molecular dynamics.

Eucommia ulmoides gum (EUG), a sustainable plant-derived natural polymer, was functionalized via three distinct routes, including vulcanization, epoxidation, and hydroxylation to yield vulcanized (VEUG), epoxidized (EEUG), and hydroxylated EUG (HEUG), respectively. We systematically characterized the effects of modification route and degree on the chemical structure, crystallization behavior, thermal stability, hydrophilicity, and mechanical properties of functionalized EUG and further evaluated the high/low-temperature performance, microstructure, and mechanical properties of the corresponding modified asphalt binders (VEMA, EEMA, HEMA) as a function of modifier type and loading. For VEUG, C-S cross-linking networks formed during vulcanization suppress EUG crystallization, enabling a rigid-plastic to elastic transition, while high-temperature cleavage of C-S bonds reduces its initial thermal stability. For EEUG, epoxidation breaks C=C double bonds and introduces epoxy groups to strengthen intermolecular interactions; subsequent ring-opening grafting of hydroxyl groups onto EEUG yields HEUG, which forms additional cross-links via dynamic hydrogen bonds. Increasing modification degree for both EEUG and HEUG reduces their number- and weight-average molecular weights with narrower distribution, diminishes crystallinity, enhances thermal stability and hydrophilicity, and drives a rigid-plastic to elastic transition, characterized by decreased strength (0.65 MPa < σ_HEUG < σ_EEUG < 10.18 MPa) and markedly improved ductility (143.6% < ε_EEUG < 262.0%, 679.9% < ε_HEUG < 1360.3%). In asphalt binders, VEUG’s cross-linked network endows VEMA with refined more abundant bee-like microstructures, drastically boosting high- and low-temperature performance: relative to pristine EUG-modified asphalt (EUGMA), VEMA’s DMT modulus decreases by 94%, and adhesion increases by 87%. EEMA forms covalent bonds with polar asphalt components via epoxy groups, while HEMA constructs a hydrogen-bonded cross-linked network; both effectively inhibit asphaltene aggregation. With increasing modifier loading, EEMA and HEMA exhibit increased modulus, reduced adhesion, and gradually improved high- and low-temperature performance, except for the non-significant high-temperature enhancement of HEMA at higher loadings.

Conventional thermoplastic polyurethane (TPU)-modified asphalt suffers from poor high-temperature performance, and the influence of aggregate skeleton structure on the performance of TPU-based modified asphalt mixtures remains insufficiently understood. TPU-modified asphalt and SMC-grafted TPU composite-modified asphalt were prepared via in situ prepolymerization, using base asphalt (BA) and SBS-modified asphalt as control binders. Four types of AC-16 asphalt mixtures were designed and systematically evaluated in terms of volumetric properties, low-temperature mechanical behavior, pavement performance, and aging resistance. The coarse aggregate void filling (CAVF) gradation was introduced to compare performance differences among mixtures with identical binders but distinct aggregate skeleton structures. The results demonstrated that TPU/SMC composite modification enhanced the high-temperature performance of asphalt mixtures while maintaining satisfactory low-temperature cracking resistance. The dynamic stability of the composite-modified mixture was over 60% higher than that of the base mixture, while its maximum flexural tensile strain at low temperature exceeded that of the conventional SBS-modified system. After aging, the freeze–thaw splitting strength retention rate of the composite-modified mixture reached 98.5%, and its aging resistance outperformed that of the SBS-modified mixture. CAVF gradation further improved the performance of TSMA mixtures, increasing fatigue life by 22.5% while enhancing rutting and moisture damage resistance. These findings demonstrate that CAVF-based aggregate structure optimization can further improve the pavement performance of TSMA mixtures and provide an experimental basis for material selection and gradation design of steel bridge decks and cold-region asphalt pavements.