Asphalt pavement is a critical component of transportation infrastructure, and the development of renewable bio-based modifiers offers a promising strategy for improving asphalt performance and sustainability. This research involved the synthesis of three asphalt modifiers (Oxa_1, Oxa_2, and Oxa_3) by regulating the molar ratio between epoxidized soybean oil (ESO) and methylenediphenyl diisocyanate (MDI). The relationship between the modifiers and asphalt properties was analyzed using molecular dynamics (MD) simulations and multi-scale experimental characterizations. The results indicate that the molecular structure of the modifiers significantly influences the performance of modified asphalt. The dual-arm Oxa_2 structure demonstrated the highest degree of physical entanglement and the lowest fractional free volume (FFV), attributable to its symmetrical comb-like configuration, which offers superior resistance to permanent deformation. In contrast, the three-arm star-shaped Oxa_3 enhanced cohesive energy density and complex modulus by introducing a higher density of polar oxazolidinone rings and MDI-derived groups, thereby promoting the formation of a stronger three-dimensional physical cross-linking network. Although Oxa_3 provided the most pronounced improvement in high-temperature stiffness, the single-arm Oxa_1 showed superior low-temperature stress relaxation owing to its higher FFV and greater chain flexibility. Finally, grey relational analysis (GRA) confirmed the close correlation between molecular descriptors and rheological indicators, demonstrating that the molecular architecture of ESO-MDI modifiers governs the multi-scale performance of modified asphalt. This study provides a theoretical basis for the molecular design of sustainable bio-based asphalt modifiers. METHODS: MD simulations were performed using Materials Studio with the COMPASS II force field. Van der Waals interactions were calculated using the atom-based method, while electrostatic interactions were treated using the Ewald summation method. Periodic boundary conditions were applied to eliminate boundary effects. Temperature and pressure were controlled using the Andersen thermostat and Berendsen barostat, respectively.

ABSTRACT Semiflexible pavements (SFPs) offer a unique combination of asphalt flexibility and cement rigidity to combat pavement rutting. Polyurethane (PU)-modified asphalt is a chemically reactive binding material. Unlike conventional physical modifiers, the PU prepolymer undergoes chemical reactions with both the asphalt and the grout, resulting in chemical bonding. This research involved the preparation of modified asphalt utilizing two PU prepolymer types: linear PU molecular structure (MP) and interpenetrating network structure (CMIP). The implications during the initial and final stages of grout with PU-modified asphalt and its repercussions on the failure behavior of cement-asphalt in SFP were analyzed by a series of mechanical and microscopic experiments. The results indicated that incorporating CMIP into asphalt significantly enhanced its high-temperature modulus, deformation resistance, and viscosity, although its low-temperature flexibility was inferior to that of MP. Fluorescence microscopy analysis revealed that the cured PU formed a dense structural network within the asphalt matrix in the final stage, with asphalt enclosed within these aggregates. The viscosity increases 2.86 and 2.72 times from the initial curing stage to the final stage, respectively, in CMIP and MP. The fracture energy of MP is determined to be 2,673 J/m2, equivalent to 2.81 times that of final curing stage. For CMIP, the value is 3.02 times. The network structure and reactivity of PU prepolymers played a crucial role in improving the water damage resistance, fatigue resistance, and crack resistance of SFP. This enhancement was mechanistically attributed to the active PU prepolymers improving the wettability of the asphalt surface, thereby reinforcing the cement–asphalt interface. This research offered valuable insights into the utilization of PU in SFP materials, presenting it as a promising option for sustainable road construction.

Polyurethane (PU) modified asphalt, characterized by a controllable network structure, has garnered significant attention due to its remarkable resistance to high-temperature deformation. Nonetheless, a systematic understanding of the curing time and the evolution of the crosslinking structure remains insufficient. This study employs a combination of molecular dynamics simulations and experimental characterization to elucidate the microstructural evolution and the rheological response mechanisms of polyurethane modified asphalt throughout the curing process. The results demonstrate that the curing reaction of polyurethane in asphalt exhibits first-order kinetics. The reaction rate constant is 0.0432 min⁻¹ . Molecular simulation results indicate that moderate crosslinking, particularly at a 50% crosslinking degree, enhances the interfacial compatibility between polyurethane and asphalt by improving intermolecular contacts, optimizing free volume, and strengthening polar interactions. In contrast, excessive crosslinking results in a dense and rigid three-dimensional network, which restricts molecular motion and diminishes intermolecular interaction forces. Rheological tests reveal that prolonging the curing time can improve the high-temperature rutting resistance of the material. This phenomenon is evidenced by a reduction in non-recoverable creep compliance and increases in creep recovery rate, rutting factor, and zero shear viscosity. However, this enhancement in performance is accompanied by a decline in low-temperature stress relaxation capability and an increase in low-temperature modulus. Euclidean distance matrix analysis further demonstrated a non-linear relationship between experimental curing time and simulated crosslinking degree. During the early curing phase, the system tends toward a low crosslinking structure, while the network structure develops rapidly during the mid-curing phase. At 60 min, the crosslinking degree was approximately 70%. By 90 min, it closely resembled the 90% crosslinked system. This study clarifies the evolution mechanism of the crosslinked network in PU modified asphalt, offering a theoretical foundation for optimizing the balance between high- and low-temperature performance through precise regulation of curing time.

Polyurethane(PU)-modified asphalt has excellent strength and toughness, while the influenceof PU composition and distribution on asphalt performance remains unclear. Thisresearch incorporates different compositions and dosages PU with asphalt toinvestigate the formation process of the PU cross-linked network. The PU wasextracted from asphalt and compared with synthesized PU to analyze theinteraction between PU and asphalt. The results reveal that the PU cross-link networkstructure enhances the temperature performance of asphalt. The enhancementmechanism primarily hinges on the establishment of a chemically cross-linkednetwork. With higher PU dosage, a more continuous network structure emerged.The PU dispersion transitions from a uniform distribution at the nanoscalelevel to a structure characterized by micron-scale particle aggregates. Theoptimal dosage of PU is 20%. Considering the low-temperature flexibility, thecontent of hard segment should be less than 40%. This research offers avaluable theoretical foundation for improving asphalt performance.

A polyurethane semi-prepolymer was introduced as a new modifier for asphalt. The performance of the polyurethane semi-prepolymer-modified asphalt were compared with SBS-modified asphalt. The results of infrared spectroscopy and fluorescence microscopy indicate that there is a chemical reaction between the polyurethane semi-prepolymer and the asphalt, while the SBS and the asphalt are physically cross-linked. The dynamic shear rheometer (DSR) tests indicate that the polyurethane semi-prepolymer-modified asphalt exhibits resistance to deformation at high temperatures, remarkable elastic recovery, minimal stress sensitivity, and higher viscosity. However, its low-temperature performance is inferior to that of SBS-modified asphalt. Based on the asphalt mixture rutting test, the study confirms the excellent rutting resistance of polyurethane semi-prepolymer-modified asphalt. Moreover, the three-point beam bending test and semi-circular bending test (SCB) indicate that the low-to-medium temperature cracking resistance of the polyurethane semi-prepolymer-modified asphalt mixture is inferior to that of SBS-modified asphalt. Therefore, polyurethane semi-prepolymer-modified asphalt exhibits significant application potential in high-temperature regions and on heavy-duty roadways.

This study aims to investigate the failure modes at the interface of semi-flexible pavement (SFP) materials. The cohesive and wetting properties of asphalt materials, as well as two types of grout (early strength cement grout - ELS and high strength cement grout - CHS), were evaluated through pull-out tests and contact angle experiments. The rheological properties of the grout/asphalt mortar were assessed using dynamic shear rheometer (DSR) testing. The interaction coefficient, complex shear modulus, and complex viscosity coefficients of the grout/asphalt mortar were calculated to analyze the interaction between the grout and asphalt. Failure modes were identified through image analysis of semi-circular bending test (SCB) specimens. Results indicate that ELS specimens exhibit a lower grout/asphalt interface failure ratio compared to CHS specimens, due to the superior wettability and interaction of ELS grout. As the temperature increases, the proportions of cement fracture and aggregate failure decrease, while the proportion of asphalt cohesive failure surfaces increases. Furthermore, the bonding strength of SBS-modified asphalt with the grout exceeds that of pure asphalt.

CONTEXT:Asphalt recycling represents an advanced, eco-friendly pavement rehabilitation technology where proper rejuvenation of aged asphalt ensures the economic viability of reclaimed asphalt pavement (RAP). In this study, molecular models of raw asphalt and aged asphalt were constructed using Materials Studio. The reaction between the epoxy resin and curing agent was automated via a Perl script, establishing molecular dynamics models of epoxy asphalt and epoxy-aged asphalt containing approximately 30% epoxy resin and achieving a cross-linking rate of 87.5%. Through a dual-method approach-directly analyzing cross-linked epoxy resin's impact on aged asphalt molecules and comparatively evaluating aging degradation in virgin versus epoxy asphalt-we employed cohesive energy density, free volume fraction, and mean square displacement analyses. Results demonstrate that cross-linked epoxy resin weakens strong polar interactions between aged asphalt molecules, increases molecular free volume and diffusion capacity, and significantly inhibits polar molecule aggregation, thereby collectively enhancing aged asphalt performance. Rheological testing confirms that epoxy resin partially restores the viscoelastic properties of aged asphalt, providing macroscopic validation of molecular simulation results. This multi-scale verification advances fundamental understanding of epoxy-recycled asphalt (ERA) systems and establishes theoretical foundations for optimizing pavement performance in sustainable regeneration applications. METHODS:To investigate the effect of epoxy polymers on the aging behavior of asphalt, molecular models of virgin asphalt, aged asphalt, epoxy asphalt, and epoxy-aged asphalt were constructed using the Amorphous Cells module of the Materials Studio 2020 software. Molecular dynamics simulations of these four asphalt models were then performed using the Forcite module, with atomic and molecular interactions described by the COMPASS II force field.

Polyurethane (PU) is recognized as a promising material for asphalt modification due to its tunable physicochemical properties. To reduce reliance on petroleum-based polyols, this study employed bio-derived castor oil (CO) combined with polytetrahydrofuran (PTMEG), diphenylmethane diisocyanate (MDI), and 1,4-butanediol (BDO) as raw materials. Polyether-type PU (PTMEG-MDI) and polyether/castor oil composite PU (PTMEG/ CO-MDI) were successfully synthesized through controlled hard segment content (Ch) and isocyanate index (r), followed by application in asphalt modification. The structure-property relationships were investigated using FTIR, TGA, DSC, and mechanical testing systems. The results demonstrated that the incorporation of CO significantly enhanced the comprehensive performance of PU composites. Compared to the single polyether-type PU, the PTMEG/CO composite PU exhibited better thermal stability, mechanical strength, and elongation at break. Increasing Ch continuously improved the Shore hardness and tensile strength of PU, while reducing its thermal stability and elongation at break. When r reached 1.2, the PU molecular chains attained an optimal stability equilibrium state. FTIR analysis confirmed chemical reactions between the -NCO groups in PU and active components of asphalt, forming characteristic urethane absorption peaks, thereby achieving chemical bonding modification. In terms of asphalt modification performance, the PTMEG/CO-MDI system notably enhanced high-temperature stability while maintaining favorable low-temperature performance. This research establishes fundamental correlations between PU molecular design parameters (Ch and r) and asphalt modification performance, providing theoretical guidance for developing eco-friendly high-performance asphalt modifiers.

Semi-Flexible Pavement (SFP) material, prepared by pouring cement-based grouting material into the voids of a porous asphalt mixture, has good load bearing capacity and excellent resistance to rutting. It is gaining increased applications in areas where permanent deformation of asphalt mixtures is a concern. When applied as the pavement surface course, the major distress observed in SFP is cracking. Currently, there is a lack of comprehensive understanding of the cracking mechanism of SFP. To improve such understanding, this study investigated the effects of fracture parameters of asphalt mortar and asphalt-aggregate interface on the crack resistance of SFP materials through laboratory experiments and numerical simulation using the finite element method. Firstly, a three-point bending test was performed on a beam SFP specimen. A multi-scale mesoscopic heterogeneity model was then established based on the mesoscopic structure of the specimen and calibrated and validated using the load-displacement curves and the cracking process features. With the validated model, the effects of different fracture parameters on the beam cracking process were investigated. It was found that the load-bearing capacity of SFP increased with the increase of the tensile strength of asphalt mortar and asphalt-aggregate interface in a certain range, while the crack propagation rate after crack initiation also increased. An increase in the fracture energy of asphalt mortar and asphalt-aggregate interface delayed the crack propagation rate, but with an attenuative effect with the increase of fracture energy. Based on the actual test conditions, the desirable range of key cracking parameters of SFP materials were recommended.

In order to regulate the directional transfer and collection of heat in pavements, a novel solution has been proposed, named Umbrella-Shaped Heat-induced Channels (UHC). This UHC is composed of carbon fibers with high axial thermal conductivity and a heat-induced layer. A finite element heat transfer model is employed to analyze the heat transfer behaviors of asphalt mixtures. And an indoor irradiation experiment is conducted for feasibility verification. The results indicate that enhancing the thickness of the heat-induced layer or increasing the disparity in thermal conductivity between the heat-induced layer and asphalt mixtures can enhance the oriented heat transfer effect of UHC. The heat-induced layer boosts the horizontal heat flux of the UHC by 60.3% compared to the side without the heat-induced layer. This enhancement is attributed to the secondary thermal convergence effect of the heat-induced layer, which further amplifies the thermal induction and heat collection capabilities of UHC. This phenomenon is crucial for achieving directed heat conduction. The designed UHC can enhance the heat transfer efficiency of the asphalt pavement in the designated direction. Furthermore, it can alleviate the heat island effect, address permafrost thawing and high-temperature rutting issues, and enhance the efficiency of solar energy harvesting on pavements.

Autonomous Rail Rapid Transit (ART), featuring multi-axles, high tire pressure, and complete channelization, leads to severe rutting on conventional asphalt pavements. Semi-flexible pavement materials (SFP) were applied to ART corridors to mitigate rutting. Mechanical response characteristics were obtained by embedding sensors to understand the interaction between ART and SFP. Results found that the damage of corridor pavement shifted from rutting to top-down transverse cracking after adopting SFP. Nonresidual longitudinal tensile strains primarily caused top-down transverse cracking. The compressive stress at the bottom of corridor pavement caused by ART is 41%, 36%, and 58% higher than that of the BUS, respectively, under the condition of constant speed, acceleration, and deceleration. The maximum strain response caused by ART under a high-temperature environment was ten times higher than that of buses. These findings can provide data support for numerical simulations, material failures, and structural damage of ART corridors. Highlights 1. Mechanical responses of semi-flexible pavement materials influenced by Autonomous Rail Rapid Transit (ART) were first captured using sensors. 2. ART with high tire pressure exhibits a multi-axial cumulative effect in high-temperature conditions, resulting in pavement strains that can be up to ten times those of buses. 3. After adopting semi-flexible pavement, the damage in ART corridors shifted from rutting to top-down transverse cracking. 4. Nonresidual longitudinal tensile strains are the underlying cause of top-down transverse cracking.

Graphene and its derivatives have garnered significant attention as novel nanomodifiers in the asphalt industry. Despite its vast potential, poor compatibility and dispersion between graphene and asphalt have been persistent challenges for researchers. To prepare well-dispersed graphene materials, polyvinylpyrrolidone (PVP) was grafted onto water-soluble graphene (WG), resulting in PVP-WG composites. This PVP-WG composite was introduced into matrix asphalt as a modifier to improve the compatibility and dispersion of graphene with asphalt. Various advanced techniques such as Fourier transform infrared spectroscopy, laser particle size analyzer, scanning electron microscopy, and X-ray diffraction confirmed the successful attachment of PVP to the surface of water-soluble graphene, thereby increasing the spacing between WG and promoting the intercalation of asphalt molecules. The loose structure of PVP facilitated the effective binding between WG and asphalt molecules. The multiple stress creep recovery and dynamic shear rheometer tests demonstrated that PVP-WG was effective in enhancing the elastic recovery performance, high temperature resistance to deformation, and viscoelastic properties of the asphalt binder. In addition, the results of the bending beam rheometer test showed that PVP-WG slightly reduces the low-temperature performance of asphalt, but PVP significantly improves the low-temperature cracking resistance of WG-modified asphalt. This study provides valuable insights into the potential application of graphene in asphalt pavement materials.

This study aims to investigate the failure mechanism of semi-flexible pavements (SFP) under freeze-thaw conditions and to provide theoretical support for optimizing the material properties. By simulating the freeze-thaw damage process of SFP in actual service scenarios and combining various experimental methods, the strength characteristics and microstructural change rules of SFP in the freeze-thaw process are systematically analyzed. The study used freeze-thaw tests to simulate the real environment, combined with indirect tensile tests (IDT) and three-point bending tests to evaluate the mechanical properties of SFP. To further investigate the failure mechanism, scanning electron microscopy (SEM) was used to observe the interfacial changes between asphalt and early-strength sulphoaluminate cement (JGM301). Additionally, CT scanning was used to capture the structural changes of SFP during freeze-thaw cycles. The results showed that freeze-thaw cycles significantly and negatively affected the split tensile strength of SFP. SEM observations revealed that cracks appeared at the asphalt-cement interface (ITZ), the cement-SBS bond weakened, and the structure of the cement itself became loose. CT revealed structural changes such as cracking at the interface of the two-phase material, creation of new voids, and linkage of old voids during freeze-thawing of the SFP. In summary, the reduction in adhesion at the cement-asphalt interface and the frost swelling of JGM301 are the main reasons for the damage of SFP in freeze-thaw cycles. This study provides an important basis for an in-depth understanding of the freeze-thaw damage mechanism of SFP and optimization of its performance.

为探究养护条件对半柔性路面材料抗裂性能的影响规律,首先,基于抗压和抗折试验,表征了2 种不同强度灌浆料在3 种不同养护条件下的强度特性.其次,基于弯拉荷载模式的半圆弯拉试验(SCB)和间接拉伸试验(IDT),研究了灌注后的2 种半柔性路面材料在3 种不同养护条件下的宏观抗裂力学性能.最后,采用扫描电镜(SEM)分析了不同养护条件和不同养护龄期水泥基灌浆料的微观结构,揭示了养护温度与养护湿度对水泥基灌浆材料的水化产物和分布的影响,并结合宏观力学性能探明了养护条件对抗裂性的作用机理.结果表明:养护条件对浆料强度、断裂特性和微观结构均有明显影响,浆料3d 抗压强度与SCB 测试的峰值荷载具有较好的线性相关性;在25 ℃时,室温养护条件SFP 试件的抗裂性能最佳.在-10 ℃ 时,普通型浆料的SFP 试件在高温养护时性能最佳,早强型浆料的SFP 试件则在室温养护条件时性能最佳;浆料微观结构致密程度与其抗压抗折强度有较好的对应性,浆料微观结构致密时SFP 试件在25 ℃具有较好的抗裂性能,而浆料具有微孔结构,与沥青形成良好的界面连接,其SFP 试件在-10 ℃ 时具有较好的抗裂性能.研究结果对半柔性路面材料的铺筑与应用具有指导意义.

为研究环氧沥青的高温性能,制备了环氧树脂掺量不同的改性沥青进行动态剪切流变试验并探究了固化时间对环氧沥青流变性能的影响.结果表明,随着环氧树脂含量的增加及固化时间的延长,沥青的复数剪切模量G*和车辙因子G*/sinδ增大,相位角δ和蠕变变形量减小,这表明环氧树脂改性使沥青的刚性明显增强,有利于提高其抗车辙性能.基于分子动力学模拟了环氧沥青的流变行为,通过对内聚能密度(CED)、自由体积分数(FFV)和均方位移(MSD)的分析,揭示了环氧树脂改善沥青高温稳定性的内在机理.从宏观和分子尺度研究了环氧沥青的高温性能,为丰富环氧沥青材料的研究方法和评价手段提供了新的思路.

CONTEXT:Graphene oxide(GO) has been widely used in asphalt modification due to its excellent properties. To reveal the interaction effect between GO and asphalt materials, the microscopic behavior and molecular structure changes of asphalt and GO/asphalt were investigated by molecular dynamics (MD) simulations. Mean square displacement (MSD) results showed that GO significantly inhibited the diffusion of molecules of asphalt components. Radial distribution function (RDF) results that GO destroys the original sol-type structure of asphalt. Simultaneously, GO adsorbed resins at low-temperature, adsorbed asphaltenes at high-temperature, and dispersed as a dispersed phase in the light components. The concentration of the dispersed phase in the asphalt colloidal structure was increased and the mutual attraction was enhanced. This improves the deformation resistance at high temperature, but weakens the ductility at low temperatures.METHODS:To investigate the mechanism of action of GO-modified asphalt, the asphalt model and the GO/asphalt composite system model were constructed using the Amorphous Cell module in Materials Studio 2020 software. Subsequently, molecular dynamics simulations of the GO/asphalt composite system were performed using the Forcite module, while the interactions between atoms and molecules were described using the COMPASS II force field.

电子导向胶轮系统(智轨)是一种能缓解交通压力的交通新制式,因其重载、渠化、多轴的交通特点,导致路面典型车辙病害问题十分突出,严重限制了其在交通领域的应用和发展.基于株洲市电子导向胶轮系统工程,研究了半柔性路面技术运用于系统廊道路面结构的设计及施工方法.通过在路面层中埋设传感器跟踪观测了路面在电子导向胶轮系统车辆运行过程中的应力应变响应,并与普通公交车进行了对比分析.测试了路表弯沉值、平整度、抗滑性等关键指标并表征了其应用效果.传感器数据表明:相比于普通公交车,系统车辆增大了路面应变响应,加速了路面破坏;半柔性路面能显著降低路面弯沉.应用 1 a后,电子导向胶轮系统路面未产生车辙病害,路面使用效果良好.电子导向胶轮系统路面修建中采用半柔性路面技术,有效解决了传统路面无法满足其行驶要求的难题,有利于该类重载渠化交通的推广和应用.

Cracking is one of the main diseases of cement grouted asphalt mixture (CGAM). This paper aims to disclose the whole process failure characteristics of CGAM under different loads. Three types of tests under acoustic emission monitoring were designed to observe the performance of CGAM under indirect tension, bending tension and compression. Stone matrix asphalt (SMA) was used as the control group. The results show that the failure process of CGAM can be divided into three stages. Large damage will be produced in one or more short periods. The cracking of cement mesh is one of the main factors to form cracks in CGAM, and its brittleness leads to the proportion of macro cracks of CGAM in each stage being greater than that of SMA. The proportion of shear failure of CGAM is higher than that of SMA, so more attention should be paid to its shear resistance in material design.

Semi-flexible pavement (SFP) has been widely used for ant-rutting performance and resistance in heavy load conditions. The asphalt mixture skeleton was the central part in the complex-skeleton material system. However, few studies have been made on the connection of asphalt mixture skeleton composition and performance on semi-flexible pavement material. Therefore, the relationship between the skeleton gradation volumetric characteristic and mechanical properties of semi-flexible pavement material was investigated. Eight gradations with different coarse aggregate contents were constituted. The mechanical performances were conducted to establish the relationship between primary gradation performance. The result shows that the porosity of the asphalt matrix and Cantabro abrasion test are related to the composition of gradation. The tensile performance, shear characteristics, and compressive strength were affected by the voids filled asphalt (VFA), porosity, and fine aggregate to asphalt ratio (FB), respectively. The Burgers model accurately reflected the creep curves of the semi-flexible pavement material specimens. The creep modulus was related to the VFA, porosity, and effective asphalt content (Pbe). The gradation design parameters of open-gradation asphalt mixtures for semi-flexible pavement materials could be obtained based on the target performance. It is possible to reduce material testing times based on the correlation analysis effectively.