Semiflexible pavement (SFP) is a composite material composed of porous asphalt mixtures and cementitious grout substances. Numerous asphalt-grout interfacial transition zones (ITZ) exist within this material and present inherent susceptibility to cracking. However, the microstructural changes within these interfaces remain inadequately understood due to the material's complex and multiphase nature. This study investigates the microstructural characteristics of the asphalt-grout ITZ and its relationship with SFP's macroscale performance, focusing on silane coupling agent modification. Atomic force microscopy (AFM) was first employed to analyze the effects of curing age, grout strength, and interfacial modification. Then, scanning electron microscopy (SEM) analysis was used to explore the correlation between the micromorphology and macroscopic mechanical properties of the asphalt-grout ITZ. Finally, a semicircular bending test was applied to test the crack resistance of SFP after interface modification. The results show that immersion of the porous asphalt mixture specimens with the interface modifier can enhance the microscopic properties of the asphalt and cementitious grout materials. The ITZ between asphalt and grout forms a double-layer structure, with smoother interfaces observed after applying the interfacial modifier. The width of the asphalt-grout ITZ may exceed 30 μm after SFP formed for 28 days. Microcracks in the asphalt-grout ITZ were significantly reduced after interface modification. These findings provide insights into proactive strategies for reducing cracking at asphalt-grout interfaces, thereby enhancing the overall performance of SFP.

Urban rail transit is an energy-intensive sector with substantial carbon emissions, particularly during its operational phase. Despite the rapid emergence of energy-saving technologies, the lack of systematic quantification of their carbon emission reduction efficiencies hinders comparative evaluation and informed decision-making. This study addresses this gap by developing a carbon emission calculation framework for key energy-saving technologies, incorporating an enhanced Bass diffusion model to forecast future emissions. A marginal abatement cost analysis and a Multi-Constraint Interior Point Method are further employed to formulate an optimized, multi-dimensional integrated strategy encompassing energy, vehicle, storage, and network systems. Results reveal that, in terms of carbon emission impact, the technologies rank as follows: Permanent Magnet Synchronous Motors (PMSM) traction systems, Regenerative Braking Systems (RBS), Life-Cycle Smart Environmental Control Systems (LCSMS), and various energy storage systems. While Flywheel Energy Storage (FES) technology and LCSMS initially exhibit high marginal abatement costs, these decline significantly before 2030. In contrast, Photovoltaic (PV) generation technology maintains the lowest marginal costs throughout. Investment optimization shows that the shares allocated to PV and LCSMS increase linearly, jointly approaching 85% by 2060. Consequently, investment in PV and LCSMS should be progressively scaled up to enhance carbon reduction performance. This study provides a theoretical basis for the formulation of urban rail transit policies and supports the achievement of the dual carbon strategy goals, holding significant theoretical and social value.

The Traffic Speed Deflectometer (TSD) is increasingly utilised as a nondestructive tool for measuring continuous deflections in asphalt pavements. These deflections are calculated from real-time measurements of deformation velocities recorded using the device’s laser vibrometer, combined with the vehicle's travelling speed. However, existing methods for calculating TSD deflections are limited by accuracy and computational efficiency constraints. To address these issues, an improved deflection calculation method was developed. First, finite element (FE) simulations were performed to clarify the deflection slope distribution characteristics of typical flexible and semi-rigid pavements under various conditions. Various fitting curves were then applied to the deflection slope data to identify the most suitable models, and an improved curve area integration method was employed to calculate the corresponding deflection values. Additionally, the impact of different subgrade moduli on the far-end deflection basin of semi-rigid pavements was analyzed, allowing for the determination of the zero-response position of the deflection slope, leding to a proposed correction method for TSD measurements. Finally, the improved deflection calculation method was validated through comparative error analysis with TSD-measured values and FE model results, demonstrating its accuracy and reliability. The findings are expected to support more precise TSD deflection basin determination, improving pavement condition assessment.

Semi-flexible pavement (SFP) is extensively used in airport and tunnel pavements due to its high strength and toughness. As a multiphase composite material, SFP contains widely distributed aggregate-asphalt interface transition zones (ITZ) and asphalt-grout ITZ. These ITZs are the weakest areas in SFP and are susceptible to cracking during operation. To enhance the crack resistance of SFP, this paper proposes an interface immersion method to immerse the porous asphalt mixtures in a silane coupling agent before grouting. However, the cracking mechanism and interface enhancement process of the ITZ in SFP are not clear. This paper employs atomic force microscopy (AFM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and nanoindentation (NI) to analyze the micro- and nanoscale properties of the aggregate-asphalt ITZ and asphalt-grout ITZ before and after interface reinforcement. Experiment results show that the aggregate-asphalt ITZ exhibits minimal interaction before and after enhancement, with the primary interaction occurring in the asphalt-grout ITZ, which has superior adhesion. Grout diffusion is more pronounced in the asphalt-grout ITZ, where cracks are significantly reduced after reinforcement. The element distribution in the aggregate-asphalt ITZ is uniform with a gradual transition, while the asphalt-grout ITZ shows a denser, more continuous distribution after surface immersion, enhancing mechanical properties. The width of the aggregate-asphalt ITZ remains constant (60–90 μm), while the asphalt-grout ITZ width increases notably after modification (from 60 to 90 μm to 90–120 μm). The research results can provide theoretical support for SFP design and maintenance.

Semi-flexible pavement (SFP) is a composite material comprising porous asphalt and cementitious grout. Its asphalt-grout interfacial transition zones (ITZ) are prone to cracking. While interfacial modifiers can improve ITZ crack resistance, their effects on microscopic morphology and chemical composition remain unclear, limiting the understanding of mechanisms influencing ITZ performance and the optimised use of modifiers. To achieve this challenge, the study characterised the microscopic morphology and chemical composition of the asphalt-grout ITZ in SFP, particularly those modified by immersion in a silane coupling agent solution. The asphalt-grout ITZ in SFP material is analyzed using a series of micromechanics techniques, including scanning electron microscopy (SEM) for microscopic morphology, energy dispersive spectrum analysis (EDS) for chemical components, X-ray diffraction (XRD) for phase composition, and Fourier-transform infrared spectroscopy (FTIR) for chemical bond information. The results indicate that an interfacial modifier can effectively enhance the microscopic bonding between asphalt and grout material, reducing the likelihood of tiny cracks between these two phases. The asphalt-grout ITZ exhibits a distinct double-layer structure, with altered morphology compared to the bulk material, including hexagonal calcium hydroxide crystals aggregation, which is more prone to cracking than hydrated calcium silicate (C–S-H) gel. Element distribution at the enhanced interface is more continuous, with synchronous enrichment. These findings provide insights into proactive strategies for improving crack resistance at asphalt-grout ITZ, thereby strengthening the road performance of SFP materials.

Asphalt concrete overlay is typically designed to be thin to minimise maintenance and rehabilitation costs, which makes it challenging to be compacted and may affect its bonding conditions with the existing pavement. The short-term preheating involves swiftly heating the pavement surface before overlay paving commences, aiming to enhance the bonding conditions between the overlay and the existing pavement. Implementing the preheating approach requires a comprehensive understanding of thermal behaviours exhibited by existing pavement under short-term preheating and the factors affecting it. In this research, the feasibility of using electric heating tubes as short-term preheating heat source was analysed, and a finite element (FE) model for analysing the thermal behaviour of asphalt pavements under rapid preheating was developed. The key control parameter between the heat source and the pavement were determined and calibrated by field tests. Further sensitivity analyses of the effects of multiple factors on the thermal response of the pavement during rapid preheating were conducted, and a prediction model of the maximum pavement temperature achievable through preheating was developed. The established prediction model is expected to provide references for implementing short-term preheating in pavement overlay construction.

Developed by Delft University of Technology, the tri-component polyurethane modified cold binder (PMCB) displays impressive durability and strength in asphalt mixtures, showing promise as a reliable binder for cold in-place recycling. However, when applying PMCB for rapid, in-situ recycling, the presence of moisture in reclaimed asphalt pavement (RAP) poses a significant challenge. To address this, an innovative approach involving treatment of the wet RAP with Calcium dioxide (CaO) prior to the integration of PMCB was tested. Evaluation methods used included the Indirect Tensile Test (ITT), followed by the calculation of the Indirect Tensile Strength Ratio (ITSR) to assess moisture susceptibility. Furthermore, Cantabro tests were performed to determine the material loss under abrasion and weathering conditions. These assessments underscored the feasibility of this approach. The treatment of wet RAP with CaO has proven a viable strategy for rapid in-situ recycling with PMCB, contributing to sustainable pavement construction. In addition, the research identified that a 5.5% concentration of the PMCB binder maximizes structural integrity and performance in the considered RAP.

The film thickness of asphalt mixtures is critical for determining their performance and aging durability. However, understanding of the appropriate film thickness and its influence on performance and aging behavior for high-content polymer-modified asphalt (HCPMA) mixtures is still limited. This research aims to examine the relationship between film thickness, performance, and aging behavior of HCPMA mixtures in order to establish an optimal film thickness that ensures satisfactory performance and aging durability. HCPMA specimens with film thicknesses ranging from 6.9 μm to 17 μm were prepared using a 7.5% SBS-content-modified bitumen. Various tests, including Cantabro, SCB, SCB fatigue, and Hamburg wheel-tracking tests, were conducted to evaluate raveling, cracking, fatigue, and rutting resistance before and after aging. The key findings indicate that insufficient film thickness negatively affects aggregate bonding and performance, while excessive thickness reduces mixture stiffness and resistance to cracking and fatigue. A parabolic relationship between the aging index and film thickness was observed, suggesting that increasing film thickness improves aging durability up to a point, beyond which excessive thickness adversely impacts aging durability. The optimal film thickness for HCPMA mixtures, considering performance before and after aging and aging durability, falls within the 12.9 to 14.9 µm range. This range ensures the best balance between performance and aging durability, offering valuable insights for the pavement industry in designing and utilizing HCPMA mixtures.

This research aimed to investigate the attenuation mode of the layer modulus of asphalt pavement in accelerated pavement testing (APT). A full-scale experimental section was constructed and tested using the APT facility. Two non-destructive testing (NDT) methods, named falling weight deflectometer (FWD) technique and portable seismic property analyzer (PSPA) test, were used to obtain the layer moduli of asphalt pavement during the APT test. The variation patterns of layer moduli obtained by FWD and PSPA tests were calculated and compared after the temperature was corrected to 20 ℃. It was found that the variation pattern of surface layer modulus based on field FWD measurements was consistent with the one measured from PSPA tests. That is the modulus of the surface layer increases with the APT load repetitions firstly and then decreases with the rise of the repetitions. The modulus values of the surface layer measured from PSPA tests are obviously larger than those backcalculated based on deflection basins. The ratio of the measured surface layer modulus based on the PSPA test to the backcalculated one based on the FWD test ranges between 2.06 and 2.71. The backcalculated base layer modulus always declines with the increasing loading repetitions. The attenuation patterns of the surface layer modulus and the base layer modulus in the damage stage are described as E_a=421100*N^-0.6119 and E_b=128000*N^-0.1096, respectively.

High-Content SBS Polymer Modified Asphalt Mixtures (HCPMA) combined with fibers have gained popularity in porous pavement construction due to their superior performance. Although the aging behavior of HCPMA has been extensively studied, the impact of fibers on performance and aging susceptibility remains unclear. This research investigates the influence of two representative fibers (lignin and polyester) on the raveling, cracking, fatigue, and rutting resistance of HCPMA before and after aging using Cantabro loss tests, SCB strength tests, SCB fatigue tests, and Hamburg Wheel-Tracking tests. The results indicate that in the original state, polyester fiber slightly enhances HCPMA performance, while lignin fiber shows limited or even adverse effects on cracking, raveling, fatigue, and rutting resistance. However, both fibers exhibit a more pronounced enhancement effect after short- and long-term aging. FTIR analysis reveals that fiber addition does not significantly impact bitumen oxidation and polymer degradation. The excellent properties of High-Content SBS Polymer Modified Bitumen (HCPMB) in the original state create a "masking" effect that conceals the enhancement effect of fibers, which becomes more evident after
long-term aging. Consequently, it is recommended that the performance evaluation and design of open-graded asphalt mixtures containing HCPMB be based on post-aging performance.

In a mechanistic-empirical (ME) pavement design method, the modulus of asphalt concrete (AC) is essential. The in-situ AC modulus can be obtained by the surface wave method (SWM). However, the measured modulus needs to be adjusted to the design frequency values. This study aimed to propose a frequency adjustment method for the in-situ AC seismic modulus. For this purpose, coring and dynamic modulus tests, FWD (Falling Weight Deflectometer) tests, and PSPA (Portable Seismic Pavement Analyzer) tests were carried out in the accelerated pavement test (APT). The master curves generated by the dynamic modulus results correlated well with the moduli determined from the other tests. Based on this relationship, a frequency adjustment factor was developed for the seismic modulus of the undamaged AC layer. For the damaged AC layer, the proposed factor was modified by incorporating the effect of the damage. Finally, to validate the frequency adjustment factor, the measured maximum tensile strains in the APT were compared with the values determined from the adjusted seismic moduli. The results prove that the frequency adjustment factor is appropriate to obtain the design modulus from the surface wave test. The PSPA test is also recommended to obtain the in-situ AC seismic modulus.

The modulus back-calculation of asphalt pavement layers using falling weight deflectometer (FWD) data has become one of the most important methods of evaluating pavement bearing capacity. Several back-calculation methods have been proposed to estimate material properties. A new modulus back-calculation method called the deflection basin regulation algorithm (DBRA) has emerged recently. This algorithm requires an inertial point and two characteristic points in a deflection basin for back-calculating the moduli of three-layer pavement. However, the existing characteristic point positions are determined based on the theoretically calculated deflections and have not been verified by measured deflections. In this research, the field-measured deflection basins of different pavement structures are used to determine the optimal characteristic point positions to improve the new back-calculation method. First, the optimal point positions are determined based on the effects of the positions on the back-calculation variability. Then the back-calculated results based on the optimal characteristic points are compared to the results obtained using the MODULUS program. Finally, the improved modulus back-calculation method is also verified by the deflections from two pavement structures at different temperatures and loading levels. It was found that the optimal characteristic point positions were located at distances of 0 and 60 cm from the load center. Both comparative analysis and independent verification prove that the determined optimal characteristic point positions work well for back-calculating the layer moduli of other pavement structures. The findings of this research may facilitate the application of the DBRA for modulus back-calculation.

The modulus of an asphalt layer subjected to repeated loadings was measured to reasonably analyze the damage development therein. The ratio of the reduction in the modulus to the modulus of the undamaged asphalt layer is used to reflect the damage of the asphalt layer; the evolution of the damage with the number of the loadings was analyzed. Full-scale accelerated pavement testing was conducted to simulate the repeated vehicle loadings on the asphalt layer. Falling-weight deflectometer, pavement seismic property analyzer (PSPA), and uniaxial compression dynamic modulus tests were conducted to obtain the modulus of the undamaged asphalt layer in the unloaded area. PSPA was used to obtain the moduli of the damaged asphalt layers in the loading area; the ratios of the reduction in these moduli to the modulus of the undamaged asphalt layer were calculated. The damage development in the asphalt layer was analyzed, and a nonlinear damage-evolution model was established, which assisted in obtaining the speed of the damage development in the asphalt layers at different depths. It is found that the S-type master curve can be used to unify the undamaged moduli derived from the three tests. The results of the field-detection method are in accordance with the predictions obtained from the laboratory master curves. In addition, the regression parameter in the damage-evolution model assists in judging the speed of the damage development in the asphalt layer. The normalization result shows that the lateral asphalt layer at the outer edge of the wheel paths and that at the center of the wheel gap experience slower damage as the depth increases. The mid-depth asphalt layers at the other positions and directions experience faster damage. In conclusion, the nonlinear damage-evolution model can provide the basis for damage development judgment and lay foundation for optimizing the maintenance timing and strategy.

Asphalt concrete (AC) modulus reduction caused by repeated axle loading significantly affects pavement long-term performance; including when built on a semi-rigid layer. However, quantifying this effect is challenging. The primary objective of this paper was to monitor and evaluate modulus reduction and fatigue damage accumulation at various AC depths utilizing data obtained from two semi-rigid pavement sections. During loading, a non-destructive method, portable seismic pavement analyzer (PSPA), was used to predict the modulus ratio. PSPA test results show that the damage is nonlinear with respect to the loading passes. Also, depth and AC thickness can influence the development of damage. A developed model showed that it could predict the aforementioned nonlinear relationship. The model parameters can be used to identify the damage level at various AC depths. Unexpected compared with previous understanding, the damage in AC layers was found to increased first, then decreased, and finally increased with the depth. Since PSPA is cheap, portable, and easy to apply, this method to identify the damage level in AC layers is proven to be applicable and practical.

The temperature field of asphalt pavement with thick asphalt layer (>30 cm) was analyzed. Based on the cumulative effect of air temperature and solar radiation on pavement temperature, a regression analysis was conducted on the measured pavement temperature from four selected test sites and the obtained meteorological data. The prediction models for different sites were determined as a function of depth, average air temperature and total solar radiation. Then, the cause for the difference between the models at each site was analyzed, and the historical mean monthly air temperatures were incorporated into the model. The model can be applied to the pavement temperature prediction in different areas. The results show that the model has high applicability and high accuracy.

Asphalt pavement is a multi-layer continuous structure with an interlayer bonding condition that can greatly influence its bearing capacity and must be monitored over the whole service length. Hence, proper maintenance and rehabilitation measures are taken and better feedback can be made for the design. Nevertheless, asphalt pavement interlayer bonding condition plays a hidden role and is difficult to quantify unless applying damage discovery techniques like drilling core process. The original structure is destroyed by the damage detection approaches, the results also suffer from low coverage rate and high dispersion, therefore, actual engineering demands are not satisfied. Here, some recent methods are briefly presented based on asphalt pavement interlayer bonding condition non-destructive diagnosis and their restrictions are discussed. Moreover, a new technique is provided with the merits of utilizing only mechanical simulation and overall superficial distresses condition evaluation index with high accuracy. This simulation procedure adopts bridging principles to build a connection between asphalt pavement superficial distresses and asphalt pavement micro mechanic parameters. It uses a structure behavior equation capable of identifying four typical deterioration modes and has specific physical meaning parameters to predict asphalt pavement overall superficial distresses. The established model allows the asphalt pavement interlayer bonding acting as a hypothetical input variable. The known input variables include easily obtainable design parameters of the asphalt pavement structure, historical superficial distresses, surface deflection, traffic load, and environmental factors, however, the output is the predicted asphalt pavement overall superficial distresses condition. The asphalt pavement interlayer bonding condition is defined by contrasting the theoretical asphalt pavement overall superficial distresses conditions between its complete bonding condition and discontinuous bonding condition to a certain degree. Examples in parts of the Jingha highway show that great discrepancies exist between theoretical asphalt pavement overall superficial distress in the condition of complete interlayer bonding and actual asphalt pavement overall superficial distress. The actual asphalt pavement sections in overall superficial conditions are deteriorated much faster than normal ones. By setting the asphalt pavement interlayer bonding continuations as 75% and 90% for K315-K316 section and K316-K317 section, respectively, the revised and predicted overall superficial distresses of the theoretical asphalt pavement are consistent with the real ones. The hypothetical values are then chosen as the diagnosed quantitative asphalt pavement interlayer bonding continuations and are proven to be correct through drilling core sample results. The analyses in other sections show that middle traffic volume asphalt pavement structure is quite weak when its interlayer bonding continuation is 70%, and under this value, its bearing capacity is almost equivalent to the situation when its interlayer bonding continuation is 0%; when its interlayer bonding continuation is 85% or more, its bearing capacity is almost equivalent to the situation where its interlayer bonding continuation is 100%. This proposed non-destructive diagnosis method for asphalt pavement interlayer bonding condition is effective and shows good application prospects in road engineering.

The modulus of asphalt mixture is traditionally measured from the laboratory dynamic modulus test. However, different laboratory test methods often lead to obviously different test results. To evaluate the moduli of asphalt mixtures as constructed in field pavements, this study back-calculated the moduli of the pavement layers, based on measured strain data in Accelerated Pavement Testing (APT). Field tests were conducted to measure strains at different locations of the built pavement section at different temperatures and wheel motion speed. The loading frequencies of the asphalt layer subject to different motion speeds were calculated based on the duration of measured strain pulses. Subsequently, the relationship between the motion speed and the loading frequency was established. An finite element (FE) model of the pavement section was created, which was used to back-calculate the moduli of asphalt pavement layers using the measured strain data. Based on the back-calculation results at different loading conditions, the master curve of the field asphalt layer was determined. This master curve was further used to compare with that obtained from laboratory uniaxial compressive test. The relationship between the field and laboratory moduli was determined to be E_Laboratory= 1.298E_Field.

The asphalt-based pavement performance evaluation includes the derivation of the dynamic moduli and loading frequencies of pavement layers under various traffic- and climatic-induced loading conditions. The traffic-induced strain pulses and loading frequencies of commonly used (semi-rigid, flexible, and steel deck) asphalt pavements were experimentally determined by vehicular loading field tests with embedded strain gauges for different axle loads, motion speeds, and temperatures. It was found that the axle load values had no noticeable effect on the pavement loading frequency, which was mainly controlled by the vehicular motion speed. The transverse frequencies were found to be higher than longitudinal ones, while the distributions of loading frequencies by pavement depth differed for three pavements under study. The frequency values at temperatures over 35 °C exceeded those at lower temperatures, while in the temperature range from 4 to 31 °C, the motion speed vs. loading frequency relations for three pavements were nearly identical. The loading frequency f increased approximately linearly with the motion speed V, according to the unified fitting equation for three types of pavements under study, namely f = 0.127 × V. This unified equation was further proved valid to predict the dynamic modulus properties of field asphalt pavement layers. Moreover, several previous prediction models for loading frequency, including the Brown model, Ullidtz model, MEPDG procedure and Ulloa model, were compared to the results in this study. These previous models were found to overestimate the loading frequencies within the asphalt layer. The prediction errors of the Brown model and the Ullidtz model were pronounced. The loading frequencies calculated by the MEPDG procedure and the Ulloa model need to be modified by dividing 2.8 and 1.7, respectively.

To meet the high temperature and anti-reveling properties required in open-graded friction course, high content polymer modified asphalt (HCPMA) is gradually widely used in China, but the rheological, chemical and aging characteristic is not clear yet. In this paper, HCPMA with different SBS content and different base asphalt are prepared, and Pressure Aging Vessel (PAV) aging was conducted to simulate the long-term aging condition. The chemical and rheological evaluation of HCPMA before and after aging were tracked with Fourier transform infrared, gel permeation chromatography test, dynamic shear oscillatory test, master curve and multiple stress creep and recovery test. The results show that firstly, the aging of HCPMA is combined with hardening of asphalt and degradation of Styrene–butadiene–styrene (SBS) polymer. Furthermore, the addition of high content of SBS polymer can reduce the formation of carbonyl, but the degradation rate of SBS polymer is not related to the content of SBS or the type of base asphalt. Besides, HCPMA with a higher SBS content will have better rheological properties, but in consideration of economy, 9% is optimum dosage. At last, HCPMA prepared with Esso asphalt as base binder exhibits better rheological properties than HCPMA prepared with SK asphalt. However, the rheology difference reduces with the increase of SBS content and after PAV aging.

Terminal Blend (TB) hybrid asphalt binders are composed of crumb rubber, SBS polymer and polyphosphoric acid (PPA). Understanding the relationship between the chemical composition and low temperature properties has a guiding significance for asphalt modification. In this study, BBR (Bending Beam Rheometer) test, GPC (Gel Permeation Chromatography) test, FTIR (Fourier Transform Infrared) test and DSC (Differential Scanning Calorimetry) test were used to evaluate the rheological and chemical properties of TB hybrid binder and TSRST (Thermal Stress Restrained Specimen test) was conducted to estimate the low temperature properties of mixture. The results indicated that crumb rubber and SBS improved low temperature properties, while PPA had an adverse effect. Furthermore, during the degradation of crumb rubber, aliphatic component was released, which played an important role in improving low temperature properties. Finally, TB hybrid asphalt mixture also had better low temperature properties than SBS modified asphalt mixtures according to TSRST results.