交通运输工程学报

Review on cold recycling technology development of emulsified asphalt and foamed asphalt

MA Tao, LUAN Ying-cheng, HE Liang, HUANG Xiao-ming, WANG Si-qi, WANG Ning, MA Yuan

Abstract: For the key research issues in the development of cold recycling technology of emulsified asphalt and foamed asphalt, the development status of cold recycling technology was introduced. The properties of material components of emulsified asphalt and foamed asphalt mixture were analyzed. The design methods of mix ratio of cold-recycled asphalt mixture and pavement structure were summarized. The evolution law of related road performance and construction technologies and equipment were discussed. The development trend of cold recycling technology in the future was proposed. Research results show that the interaction and strength failure mechanisms between material components of cold-recycled asphalt mixture are complicated. The material properties of cold-recycled asphalt mixture can be significantly affected by the source and content of recycled asphalt pavement, the aging degree of asphalt, and the type and content of asphalt and admixture. Different design methods of cold-recycled asphalt mixture are greatly different in terms of gradation selection, asphalt grade, forming method, maintenance method, and performance evaluation indexes. Most of them employ the experimental test method to guide the design of the mix ratio. The design method of cold-recycled asphalt pavement has experienced a transformation from an empirical method to a mechanical-empirical one. It usually regards the cold-recycled materials as unbonded granular materials or asphalt bonding materials for the structural design. At present, the mechanical failure design principles conforming to the material properties of cold-recycled asphalt mixture are still lacking. As for the engineering application, the cold-recycled structure layer and its mechanical response should be fully considered. The performance requirements of resistance to rutting, water damage, fatigue, and low temperature cracking should be identified to guide the design of material composition of cold-recycled asphalt mixture. In the future, the research on the performance optimization of cold-recycled asphalt mixture should be strengthened from the two aspects of construction technology and material composition. The maintenance time evaluation system based on the mechanical index needs to be established. Meanwhile, the construction specifications of cold-recycled structure layers suitable for China's climatic conditions should be further improved. Moreover, the data detection and collection of field test roads need to be strengthed to achieve the effective calibration of the structure design equation of cold-recycled asphalt pavement.More>

2023, 23(2): 1-23. doi: 10.19818/j.cnki.1671-1637.2023.02.001

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Review on warm mixing asphalt technology

LIANG Bo, ZHANG Hai-tao, LIANG Yuan, WANG Xiao-feng, ZHENG Jian-long

Abstract: To further promote the carbon neutrality in the field of transportation, the advantages and limitations of the warm mixing asphalt technology were summarized in terms of energy conservation and emission reduction according to the research status in China and abroad. The temperature and viscosity reduction mechanisms of common warm mixing agents and warm mixing technologies and the influences of different warm mixing technologies on their properties were studied. The latest research progress of warm mixing technology in the modified asphalt mixture, recycled asphalt mixture, and other asphalt mixtures was reviewed. The effectiveness of energy conservation and emission reduction under reducing the construction temperature was analyzed when the warm mixing technology was applied in the modified asphalt mixture and recycled asphalt mixture. Then, the impacts of temperature reduction on the high-temperature performance, low-temperature performance, water stability, and fatigue performance of asphalt mixture were discussed. Research results show that the warm mixing technology has such advantages as environmental friendliness, energy conservation, emission reduction, and construction facilitation. However, it has also some drawbacks such as the high cost of warm mixing agent and the residual moisture in the warm mixing asphalt which exerts adverse effects on its performance. The commonly used warm mixing technology is mostly patented abroad, and it has been widely used in various asphalt mixtures after research, digestion, and absorption in China. Fully understanding the mechanism of warm mixing technology is crucial to the development of warm mixing asphalt materials and technologies characterized by low energy consumption, low emission, and low cost. The application of warm mixing technology in the modified asphalt mixture, recycled asphalt mixture, and other asphalt mixtures can reduce the viscosity and temperature during the construction, with remarkable effects of saving energy and reducing emission. The limitation factors of its application in engineering are the initial high cost of investment and the lack of low-temperature performance and water stability of the mixture. Exploring the scheme of combining the warm mixing technology with other types of asphalt mixtures is beneficial to promote the innovation and development of green highway. In a word, the warm mixing asphalt technology is an inevitable trend to achieve the goal of global carbon neutrality and is also one of the important ways to implement the development concept of green highway.More>

2023, 23(2): 24-46. doi: 10.19818/j.cnki.1671-1637.2023.02.002

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Review on soil solidified technologies in road engineering in China

JI Jie, LIANG Ben, HAN Bing-ye, SUO Zhi, WANG Jia-ni, YU Hai-chen

Abstract: To enhance the versatility of various soil solidified technologies in road construction and to improve the regulations of solidified soil, a comparative analysis was conducted on the solidified effects and applicability ranges of stabilizers for different soils. Additionally, the specifications of road engineering design and construction were reviewed, and their strength requirements for base and sub-base were analyzed and compared with the solidified soil specifications. The compatibility of strength ranges of different grades of solidified soils and the requirements of the road specifications was studied. The internal relation between organic solidified soil and inorganic solidified soil in the strength requirements was established by integrating the solidified strength effect with the specification requirements in real situation. Research results show that inorganic, ion, and organic soil stabilizers display good solidification effects on non-special soils like clay, etc, whereas organic soil stabilizers exhibit a wider range of application and superior performance in stabilizing special soils like laterite, etc. The overlapping interval of the different 7 d unconfined compressive strength requirements for the base specified in the highway regulations and the lower limit interval comprised of various points for the minimum 7 d unconfined compressive strength requirements were combined to form an intersection interval of [1.5, 5.0] MPa. However, the minimum strength requirement for tertiary solidified soil is 2.5 MPa, which greatly differs from 5.0 MPa in the intersection interval in the highway specifications. Considering the characteristics of solidified soil and the diverse requirements of road types and structural specifications on material mechanical properties, it is suggested to refine the grading system of solidified soils by introducing three new grades: Grade Ⅳ [3.0, 4.0) MPa, Grade Ⅴ [4.0, 5.0) MPa, and Grade Ⅵ [5.0, +∞) MPa. There is no technical requirement for organic solidified soil in the current specifications and its mechanical properties are basically close to inorganic solidified soil. Its scope of application is better than inorganic solidified soil, so it is suggested that the subsequent revision of the specifications adds organic solidified soil category for standardized application.More>

2023, 23(2): 47-66. doi: 10.19818/j.cnki.1671-1637.2023.02.003

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Self-healing behavior and microscopic mechanism of microencapsulated asphalt

JI Xiao-ping, YAO Bing-chen, SI Wei, WANG Chao-hui, YI Ke, HE Shu-peng, ZHANG Xue-jun

Abstract: In order to explore the self-healing behavior of microencapsulated asphalt and its influencing factors, microcapsules were prepared by in-situ polymerization, and the micro-mechanism of self-healing behavior of microcapsules was revealed from three aspects: stress-controlled release, capillary action, and diffusion behavior by combining macro-test and micro-test. The pull-heal-pull test of microencapsulated asphalt was carried out, the self-healing rate (the ratio of pulling strength after healing to initial pulling strength) was used as the evaluation index, and the effect rules of microcapsule content and healing time on the self-healing rate were investigated. The dynamic shear rheological test of microencapsulated asphalt was carried out, and the stress-controlled release characteristics of microencapsulated asphalt were investigated by comparing the microstructures of microencapsulated asphalt before and after the fatigue test. The horizontal and vertical capillary action of core material in micro-cracks and the diffusion process of core material in microencapsulated asphalt were visualized by the fluorescence microscope. The healing process of micro-cracks in microencapsulated asphalt was observed by the real-time video recording function in microscopic image software. The release behavior of core material in microencapsulated asphalt was investigated by testing the functional groups of microcapsule core material and microencapsulated asphalt before and after the pull-heal-pull test based on infrared spectrum. Analysis results show that the self-healing rate increases from 16.70% to 48.92% when the microcapsule dosage increases from 0 to 8%, indicating that the self-healing rate of microencapsulated asphalt increases gradually with the increase of microcapsule dosage. When the microcapsule dosage is 4%, the self-healing rate in 120 min is 1.85 times that in 10 min, indicating that the self-healing rate of microencapsulated asphalt increases gradually with the extension of asphalt healing time. Obviously, increasing the load rest period and microcapsule dosage has a positive effect on enhancing the self-healing performance of microencapsulated asphalt. The microscopic self-healing mechanism of microencapsulated asphalt is that the microcapsule shell is punctured under the stress at the tip of the microcrack, then the core healing agent is released, so that the core material flows and diffuses under the drive of capillary force, contacts with nearby asphalt and is soaked, so as to achieve the purpose of repairing asphalt microcracks.More>

2023, 23(2): 67-77. doi: 10.19818/j.cnki.1671-1637.2023.02.004

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Discrete element simulation of porous asphalt mixture clogging law

HE Liang, ZHOU Zi-dong, VAN DEN BERGH Wim, BALIEU Romain, CANNONE FALCHETTO Augusto, ZHU Ji-qing, ALEXIADIS Alessio, KOWALSKI Karol, VALENTIN Jan, CAI Hao-dong, LI Hou-jun, QIAO Ya-ning

Abstract: To reveal the pore clogging law of porous asphalt mixture, the combination study of model experiment and simulation of porous asphalt mixture clogging was conducted. The pore characteristics of the porous asphalt mixture were analyzed based on the CT-scanning and discrete element software PFC3D V5.0, and the pore data of the porous asphalt mixture were obtained. The aggregates of different particle sizes were put into PFC3D V5.0, and the compacted virtual specimens were generated according to the pore characteristics. The accuracy of the model was verified by comparing the pore images of actual specimens with the MATLAB slices. In the self-weight condition, the simulation was set with the porous asphalt mixture specimen being intruded by clogging particles with specific gradation composition. The data of indoor experiments were compared and verified. The particle sizes of clogging particles were changed, and the pore decay rates of the specimen were analyzed. The clogging-sensitive particles were identified. In the self-weight condition, the fluid simulation experiment was introduced, and the change law of specimen clogging was analyzed by changing the seepage rate of fluid. Analysis results show that the virtual specimen generated by PFC3D V5.0 has high accuracy, and the simulation reveals the clogging law of the specimen. The small particles not only accumulate at the throat position causing clogging, but also congregate and interlock with the particles of larger sizes resulting in clogging too. In the self-weight condition, the clogging is mainly concentrated at the upper 30 mm of the mixture specimen, and the size distribution of corresponding clogging-sensitive particles is 0.150-0.600 mm. The size distribution of clogging particles has a great impact on the clogging results. In the conditions of gravity and fluid, with the seepage rate increasing from 0.005 m·s^-1 to 0.030 m·s^-1, the changing rate of pore decay rate increases. In addition, the clogging particles remaining in the mixture decrease, accompanied by the reduction of the pore decay rate. Therefore, the local rainfall conditions should also be considered in the design and maintenance of drainage asphalt pavement.More>

2023, 23(2): 78-91. doi: 10.19818/j.cnki.1671-1637.2023.02.005

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Optimization on evaluation indicators of asphalt pavement surface segregation based on smartphone image acquisition method

WANG Hai-nian, WAN Tong-tong, LIU Yuan-yuan, ZHENG Wen-hua, GAO Jun-feng

Abstract: In order to optimize the evaluation indicators of asphalt pavement surface segregation, three different gradation types of asphalt mixture slab specimens were prepared in laboratory. An image acquisition method was proposed to obtain the surface images of asphalt mixture by using smartphone. The box-counting method and multifractal spectrum algorithm were used to calculate the fractal dimension and multifractal spectrum indexes of the binary image. Image-Pro Plus software was adopted to extract the concave distribution percentage and macro-structure width. The surface texture depth was tested by using the indoor sand patching method, and the mean texture depth was calculated to evaluate asphalt mixture surface segregation. The concave distribution characteristics of asphalt mixture surfaces with different gradations were analyzed. The grey relational entropy of the evaluation indicators of asphalt mixture surface segregation was studied. Research results show that the error rate of reliability analysis for obtaining binary images based on smartphones is less than 3%, indicating that the obtaining method has high repeatability. The concave asphalt mixed surface has considerable fractal characteristic, the larger the aggregate particle size, the more complex surface structure analysis is. There is a linear correlation between the evaluation indicators of asphalt pavement surface segregation based on image processing method and the mean texture depth, but the correlation varies. The surface fractal characteristic indicator of the identical asphalt mixture has wide error range, however, the concave distribution percentage index has a minimum error range, changing from -1.89% to 1.89%. The entropy correlation degree between concave distribution percentage and mean texture depth is highest, which is 0.996 2, and followed by the indexes of multifractal spectrum, fractal dimension and macro-structure width. Thus, the concave distribution percentage is recommended as a reliable indicator for evaluating asphalt mixture surface segregate.More>

2023, 23(2): 92-102. doi: 10.19818/j.cnki.1671-1637.2023.02.006

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Influencing factors and mechanism analysis for evaluation of fatigue characteristics of emulsified asphalt residues

WANG De-cai, DONG Shi, HU Lei, HAO Pei-wen, ZHANG Qing, CHEN Yuan-zhao

Abstract: The stress-strain response characteristics, fatigue damage characteristics, and fatigue life prediction of emulsified asphalt residues were investigated based on the simplified viscoelastic continuum damage (S-VECD) theory. Microscopic approaches such as Fourier transform infrared spectrometer (FTIR), scanning electron microscope (SEM), and atomic force microscope (AFM) were adopted to study the influence mechanisms of morphology structure, blending modification, and fatigue damage of emulsified asphalt residues. Research results show that the damage curves of common emulsified asphalt residues are staggered. The addition of modifiers makes the damage curves no longer staggered, and the fatigue performance of emulsified asphalt residues is improved. Furthermore, the improvement effect of the SBR modifier is more obvious. The damage curves of modified emulsified asphalt residues prepared by the EN and ASTM evaporation methods are smoother than those prepared by the DHM evaporation method, which indicates that the residues obtained by the EN and ASTM evaporation methods have stronger resistance to damage. From the perspective of the fatigue life improvement, the maximum fatigue life of common emulsified asphalt residues prepared by different evaporation methods is 56.9% higher than the minimum fatigue life, and the SBS and SBR modified emulsified asphalt residues increase by 179.1% and 67.8%, respectively. This means that the modified emulsified asphalt residues are highly affected by the evaporation methods, and the fatigue life of modified emulsified asphalt residues is the smallest under the DHM evaporation method. Functional group contents, colloid structures, and microscopic roughness will be changed by adding modifiers and adjusting evaporation methods. The DHM evaporation method is more likely to cause oxidation of modified emulsified asphalt residues and promote the production of more asphaltenes. It decreases the solubility of micelles and enhances the gelation. As a result, the fatigue performance of emulsified asphalt residues reduces, and the evaluation result of fatigue performance is affected. AFM test results suggest that the exchange condensation reaction between O^2- and H⁺ occurs in the molecular structure of modified emulsified asphalt residues prepared by the DHM evaporation method. In addition, chemical cementation structures may appear, and thus the accurate characterization and evaluation of fatigue performance of emulsified asphalt residues are affected.More>

2023, 23(2): 103-115. doi: 10.19818/j.cnki.1671-1637.2023.02.007

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Asphalt viscosity and asphalt mixture pavement performance under vibration

RONG Hong-liu, NING Zhi-kang, LI Zheng-hua, YANG Xiao-long, MENG Yong-jun

Abstract: To reduce the vast energy consumption and exhaust emissions during the construction of asphalt mixture, a vibration function was added to the traditional mixing technology to reduce the temperature required for the mixing process. The effects of vibration parameters (vibration frequency and amplitude) and test temperature on the viscosity reduction for the SBS modified asphalt were investigated by the Brockfield rotational viscosity test. The basic performance indicators (penetration, softening point, and ductility) of the asphalt were tested to reveal the effects of two vibration methods on the basic performance of SBS modified asphalt. Based on the standard, high-temperature and heavy load rutting tests, water immersion Marshall stability test, and freeze-thaw splitting test, the effects of vibratory mixing on the high-temperature stability and water stability of SBS modified asphalt mixture were investigated separately. Test results show that the vibratory mixing can significantly reduce the viscosity of SBS modified asphalt, improve the mobility of the asphalt. With the increase in the vibration parameters, the viscosity reduction effect of modified asphalt is better, and the maximum viscosity reduction rate is up to 14%. The viscosity reduction by vibration can be equivalent to the temperature viscosity reduction, and the temperature equivalent effect brought by the vibration effect is more significant with the increase in temperature. After the vibratory mixing, the viscosity property of SBS modified asphalt can be recovered, and hence, no negative impact is exerted on its basic performance. When the vibration frequency is less than 40 Hz, the dynamic stability, residual stability, and tensile strength ratio of SBS modified asphalt mixture increase with the rise in the vibration frequency. It is indicated that the vibratory mixing can improve the high-temperature stability and water stability of asphalt mixture. However, when the vibration frequency is 50 Hz, the pavement performance of asphalt mixture is consistent with that at 30 Hz. In other words, the effect of vibration frequency increase on the pavement performance of asphalt mixture is limited.More>

2023, 23(2): 116-125. doi: 10.19818/j.cnki.1671-1637.2023.02.008

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Effect of time-temperature coupling on moisture stability of RHAM in post-production stage

GAO Jie, YAO Yu-quan, WANG Di, HE Liang, LIU Zhuang-zhuang, YANG Jian-gang, ZHAO Long

Abstract: To reveal the evolution of blending degree of aged and virgin asphalt in the post-production stage of recycled hot-mix asphalt mixture (RHAM) and its effect on the moisture stability of RHAM, the temperature dissipation law and time consumption of RHAM in the post-production stage were investigated, and four typical post-production stage working conditions were constructed, with the time-temperature equivalent as the indicator. The effect of time-temperature equivalent on promoting the blending of aged and virgin asphalt was revealed by using Pb to identify the virgin asphalt, with the help of the energy dispersive spectrometer analysis. The scouring effect of rainwater on the recycled asphalt pavement under the action of tire running was simulated through the moisture-induced sensitivity test of asphalt mixture. The quantitative relationship between the time-temperature equivalent and the moisture stability of RHAM under the dynamic water scouring conditions was analyzed. The strength differences of seven types of RHAMs before and after the post-production stage in five plant-mixed hot recycled asphalt pavement projects were compared, and the effect of time-temperature equivalent on the compaction of recycled asphalt pavement was demonstrated. Research results show that the blending degree of aged and virgin asphalt is directly proportional to the time-temperature equivalent in the post-production stage. The void development of RHAM under the dynamic water scouring can be prevented by increasing the time-temperature equivalent, so as to improve its moisture stability. As the time-temperature equivalent increases by 10%, the Marshall stabilities of RHAM under unscoured, weak, medium, and strong scouring conditions increase by 0.86%, 2.94%, 2.13%, and 3.34%, respectively, and the splitting strengths before and after freeze-thawing increase by 1.24% and 0.21%, respectively. The stability of RHAM after the post-production stage improves significantly, with the increase amplitude ranging from 9.0% to 32.4%. Under the premises of ensuring the compaction temperature and standardized construction, there is no inevitable relationship between the time-temperature equivalent and the compaction quality. Since the time-temperature equivalent can improve the performance of RHAM, it is recommended to extend the post-production stage under the premise of ensuring the compaction temperature.More>

2023, 23(2): 126-140. doi: 10.19818/j.cnki.1671-1637.2023.02.009

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Quantum chemistry-based thermal and UV aging mechanism of asphalt

HU Dong-liang, GU Xing-yu, SUN Li-jun, BO Wu, WU Cheng-bin

Abstract: In order to reveal the underlying mechanisms of thermal and ultraviolet (UV) aging of asphalt at the atomic level, the aging reaction paths and corresponding potential energy parameters of asphaltenes under various temperature and UV radiation conditions were analyzed based on ab initio molecular dynamics and density functional theory. The change rules of chemical functional groups on the surfaces of virgin, thermal-aged, and UV-aged asphalt specimens were analyzed based on Fourier transform infrared spectroscopy tests, and their aging degrees were compared. Research results indicate that the involved subreactions of asphaltene aging include the cycloalkane aromatization and the formation of oxygen-containing groups triggered by O₂ or radicals induced hydrogen abstraction, as well as direct homolytic cleavage on the side chains. The aging mechanism of asphaltenes can be summarized as follows: asphaltenes lose hydrogen atoms constantly and transform into highly reactive and unstable structures under the attack of O₂ molecules or radicals, and thus their energy reduces through subsequent reactions such as molecular isomerization or adsorption of oxygen atoms. As a result, the continuous progress of asphaltene aging behavior is triggered. The increase in temperature not only accelerates the rate of aging reactions, but also triggers more types of aging reactions. The aromatization reaction has the lowest energy barrier and thus can occur at lower temperatures, followed by the formation of oxygen-containing groups, and the homolytic cleavage reaction on the side chains has the highest energy barrier and can only occur at higher temperatures. Under UV radiation, the asphaltene molecule transitions to the excited state, and its reaction energy barrier is significantly lower than that under the ground state. Therefore, it can significantly accelerate the aging reaction. Fourier transform infrared spectroscopy tests show that the aging degree of UV aging asphalt specimens is much higher than that of thermal-aged asphalt specimens, which verifies the theoretical calculation results.More>

2023, 23(2): 141-152. doi: 10.19818/j.cnki.1671-1637.2023.02.010

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Preparation and characterization of carbon nanotubes reinforced volcanic ash-based geopolymer

LI Feng, ZHANG Rong-rong, ZHOU Si-qi, YANG Zhan-ning

Abstract: To investigate the reinforcing effect and mechanism of multi-walled carbon nanotubes on volcanic ash-based geopolymer, the numbers and areas of aggregates of multi-walled carbon nanotubes dispersions at different ultrasonic times were compared by using microscopy and image recognition, and an appropriate ultrasonic dispersion time was determined. Geopolymers were prepared by mixing the dispersion, alkaline activator solution, and volcanic ash in different orders. The effects of different types and concentrations of multi-walled carbon nanotubes on the workability and mechanical properties of the geopolymer were investigated by the consistency test of the slurry and the three-point bending test and the uniaxial compression test of hardened specimens. The micro-morphologies and pore structures of the geopolymer products were characterized by scanning electron microscope-energy dispersive spectrometer and mercury intrusion porosimetry. Analysis results show that the dispersion effect of multi-walled carbon nanotubes improves with the increase of ultrasonic time. After 45 min ultrasonication, the areas of more than 85% aggregates decrease to 0-100 μm², the total ratio of the aggregate areas is less than 1%, and the average area is less than 50 μm². The order of adding multi-walled carbon nanotube dispersion before adding NaOH solution is more favorable for the uniform dispersion of fibers and the preservation of the geopolymer workability. At a mass content of 0.10%, the multi-walled carbon nanotubes have little effect on the flowability of volcanic ash-based geopolymer and can effectively enhance the mechanical properties. The functionalized multi-walled carbon nanotubes have stronger hydrophilicity and wettability, leading to a slighter impact on the workability of the slurry and a more significant improvement in the mechanical properties of the hardened specimens. The 28 d flexural and compressive strengths can increase by up to 31.0% and 15.9%, respectively, compared with the reference group. The microscopic test results show that multi-walled carbon nanotubes play bridging, filling, and nucleation roles in the geopolymer, thus achieving the improvement of the performance.More>

2023, 23(2): 153-165. doi: 10.19818/j.cnki.1671-1637.2023.02.011

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Extraction and quantification of pavement alligator crack morphology based on VGG16-UNet semantic segmentation model

ZHANG Wei-guang, ZHONG Jing-tao, HUYAN Ju, MA Tao, ZHU Jun-qing, HE Liang

Abstract: A pavement alligator crack segmentation technology was proposed based on the VGG16-UNet semantic segmentation model, and a quantitative evaluation method was developed for extracting alligator crack morphology via the proposed model. Alligator crack images were collected by a mobile camera under the conditions of dry pavement, waterlogged pavement, and road marking. A multi-scene alligator crack image dataset was established including light, medium, and heavy damages. The alligator crack image segmentation effects and corresponding segmentation indexes of VGG16-UNet, VGG19-UNet, PSPNet, SegNet, and DeepLab v3 + were analyzed to select the optimal segmentation model, and the alligator crack morphology features were extracted. Three contour fitting boundary methods of the circumscribed regular rectangle, minimum circumscribed rectangle, and convex hull were compared. The optimal fitting boundary was determined, and the area of alligator cracks was calculated. A calculation method of alligator crack fragmentation based on the coordinates of the extreme points of the contour boundary was proposed. The pavement alligator crack area and fragmentation features were analyzed accordingly. Research results show that compared with four semantic segmentation models of VGG19-UNet, PSPNet, SegNet, and DeepLab v3 +, VGG16-UNet has the smallest model parameter quantity of 14 710 464, and the training speed can reach 118 s for each training epoch. It possesses the highest prediction speed of 0.021 s for each image. Additionally, VGG16-UNet shows a precision of 81%, recall of 82%, harmonic mean of 0.81, and mean intersection over union (MIoU) of 0.73 on open-source Crack500 dataset, CrackTree dataset, and EdmCrack600 dataset. It outperforms the other four models and shows higher generalization ability. The proposed convex hull boundary fitting method gets the smallest alligator crack area. Compared with the boundary fitting methods of circumscribed regular rectangle and minimum circumscribed rectangle, the proposed method increases the fitting rate by 14.47% and 9.30%, respectively, and obtains the optimal pavement alligator crack contour boundary. The alligator crack fragmentation values calculated by the extreme points of the contour boundary can evaluate the damage level of alligator cracks, which solves the difficulty of existing pavement alligator crack fragmentation calculation.More>

2023, 23(2): 166-182. doi: 10.19818/j.cnki.1671-1637.2023.02.012

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Full-scale experiment on pressure changes inside and outside high-speed trains in tunnels

MEI Yuan-gui, WANG Zhi-jun, LYU Bo, DU Yun-chao, YANG Yong-gang

Abstract: Based on the full-scale experiment of 350 km·h^-1 Chinese standard EMUs in the scientific test section of Datong-Xi'an High-Speed Railway, the variation characteristics of pressures inside and outside the train through the whole test section were studied by combining with the working state of the pressure protection valve. The impacts of tunnel length, line slope, tunnel group and train speed on the variations of pressures inside and outside the train were analyzed. The estimation method of the maximum pressure variation in the full-scale experiment in EN 14067-5—2010 and the clause "a pneumatic sealed chamber can be formed inside the whole train" in TB/T 3250—2010 were verified by the measured data. The variation characteristics of the whole train sealing efficiency and its relationship with the pressure comfort inside the train were studied. Analysis results show that the results obtained through the calculation method of the pressure peak outside the train in EN 14067-5—2010 are largely different from the measured data. The differences between the calculation results and measured data reduce significantly after the variable substitution correction of pressure variation caused by the friction between the train and the tunnel walls. When the pressure protection valve is closed, the large difference between the pressure outside and inside the train maintains for a long time after passing the tunnel with a steep slope. The closing of the interior end door, windshield through the platform door, and driver's cab door produces almost no airtightness effects, and the whole train throughout the space can be regarded as a pneumatic sealed chamber. The pressure variation caused by the head and tail ends entering tunnels and pressure variation induced by the air friction with the train and tunnel walls are proportional to the square of the train speed. The sealing efficiency of the whole train shows a decreasing trend with the increase of tunnel length, and the decrease will cause passengers' discomfort in ears. The research results can provide strong support for the in-depth understanding of the variation characteristics of pressures inside and outside the high-speed train when passing through tunnels and further improvement of relevant test standards in China and abroad.More>

2023, 23(2): 183-198. doi: 10.19818/j.cnki.1671-1637.2023.02.013

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Weight balance problem modeling and benders decomposition algorithm design of preighter

ZHAO Xiang-ling, LI Yun-fei

Abstract: The weight balance problem (WBP) of civil aviation preighter was studied. The WBP differences between preighter, passenger aircraft, and cargo aircraft were compared. A linear integer programming model of preighter WBP was built with the combined optimization characteristics of main cargo compartment assignment problem and lower cargo backpack problem. The multi-objective function of the maximum payload and the minimum deviation of the center of gravity (CG) from the specified target was realized, including the cargo holds and their position constraints, various mass constraints, joint constraints on upper and lower cabins, as well as the CG envelope constraints of the preighter in actual operation. The benders decomposition algorithm was designed to solve the model, dividing the original problem into two parts: the main problem and the subproblem. To solve the main problem, a modified simulated annealing algorithm was proposed, which improved the coding, variation, and individual modification strategies of discrete variables. The y-check algorithm based on logical check was designed to check the complex constraints such as joint weight limits of upper and lower cabins and the CG envelope of subproblems. The benders' cut constraint model was given. Twenty groups of examples with different scales were designed by taking a B757-200 preighter as an example. The Gurobi, Lingo, artificial stowing, and the proposed algorithm were tested to verify the model. Research results show that the Gurobi has the best resolution quality and speed, whose average payload, CG deviation and solution time are 29 517.3 kg, 0.02%, and 0.13 s, respectively. The artificial stowing method is the worst, and its average payload, CG deviation, and solution time reach 27 131.9 kg, 5.26%, and 581.75 s, respectively. As an intelligent heuristic algorithm, the proposed algorithm gets a payload of 28 379.1 kg, which is slightly worse than the optimized solutions of Gurobi and Lingo. Its CG deviation is only 0.05%, which can be ignored. The average solution speed is 20.33 s, much faster than the Lingo's 7 370.65 s.More>

2023, 23(2): 199-211. doi: 10.19818/j.cnki.1671-1637.2023.02.014

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Cell transmission model considering queuing characteristics of channelized zone at intersections

HUANG Wei, HU Yang

Abstract: In order to describe the evolution law of traffic flows at urban intersections more accurately, the signalized intersection with entrance widening areas and shared lanes was taken as the research object, and the cell transmission model (CTM) was improved by considering four practical factors: queue discharge process, divergence process, optional lane changing, and shared lanes. According to the geometric characteristics of the intersection, a method to divide cells at road sections was proposed based on lane groups. On this basis, the cell sending capacity function was adjusted to reflect and model the queue discharge process. The blocking factors were introduced in the divergence process modeling to describe the interaction of spatial queuing among different lane groups. The optional lane changing behavior in the transition zone was modeled with the goal of balancing the spatial queuing of adjacent lane groups, and the conflict effect of traffic flows with different directions was considered in the modeling of shared lanes. On the basis of an actual intersection, the maximum queue length of the lane group cycle was selected as the evaluation index to verify the effectiveness of the improved CTM. Test results show that the improved CTM can simultaneously estimate the queue lengths of different lane groups. With the increase in the proportion of through traffic flows, the estimation error of the improved CTM decreases. The mean absolute error (MAE), root mean square error (RMSE), and weighted mean absolute percentage error (WMAPE) of the maximum queue length at road sections are less than 16.43, 21.36 m, and 13.51%, respectively, under different traffic scenarios. Compared with the benchmark method, the improved CTM can reduce the MAE by 15.31%-90.03% for the maximum queue length at road sections under different scenarios, and the estimation accuracy under high-traffic scenarios improves more obviously. Thus, it can be seen that the improved CTM can more accurately describe the operational characteristics of traffic flow at intersections and improve the estimation accuracy of queue length, which can be used as an important basis for the traffic management and control.More>

2023, 23(2): 212-224. doi: 10.19818/j.cnki.1671-1637.2023.02.015

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Direct sales channel pricing strategy of international cruise lines after epidemic

YANG Zhong-zhen, YANG Yun-qian, XIE Xie, GUO Wei-you, LIAN Feng

Abstract: The differences between the distribution mode of cruise products abroad and the charter mode of travel agencies in China were compared and analyzed. The reason that the charter modes of travel agencies has become a bottleneck restricting the further development of Chinese cruise tourism market was analyzed. According to the Steinberg game and Cournot game theory, a direct sales and consignment sales price game model considering consumers' choice behavior was constructed. A numerical analysis test taking one cruise line and multiple travel agencies as the objects was designed. The relationship between the price game behavior of cruise line direct sales and travel agency consignment sales and the market demand features was analyzed in the market monopolized by the cruise line, the competitive market of travel agencies, and the competitive market of the cruise line and travel agencies. Research results show that in the early development stage of Chinese cruise market, the charter mode of travel agencies is in agreement with the needs of the international cruise line for rapid market penetration, and the indirect influence of the international cruise line on the price of agency channels is weak. Therefore, travel agencies are needed to obtain a reasonable price for their cruise products. In the mature period of the market, when the number of travel agencies for cruise products is 4-6, the prices of direct sales channels and agency consignment sales channels can be guaranteed to be in a reasonable range. However, as Chinese cruise market gradually becomes mature, the efforts of the international cruise line should be strengthened to develop direct sales channels. Regulating the cost price of unit shipping space and controlling the number of travel agencies when ordering shipping space is capable of indirectly controlling the sales price of agency consignment sales channels. An effective advertisement may be achieved by negative news on the cruise epidemic, and a positive role may be played by these reports in enhancing the popularity of cruise products in the post-epidemic era.More>

2023, 23(2): 225-239. doi: 10.19818/j.cnki.1671-1637.2023.02.016

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Yaw stability control strategy of modern trackless train

ZHANG Li-wei, LIU Jin-qi, ZHANG Meng-lei, SONG Zhong-chao

Abstract: To improve the problem of poor yaw stability and path tracking performance of modern trackless trains, a vehicle dynamics model was established based on the Lagrange equation, and the influence of hydraulic rod stiffness on the vehicle steering performance was analyzed. To solve the problem that the unknown constraints in the equation made it difficult to solve its quantitative relationship, the yaw rate error and trajectory tracking error were taken as optimization objectives, and the genetic algorithm was used for offline optimization of stiffness parameters. The function interpolation method was adopted for online prediction to obtain the optimal hydraulic rod stiffnesses under different vehicle speeds and front wheel angles. To improve the vehicle trajectory tracking performance, the yaw rate tracking error and trajectory tracking error were used as the criteria to evaluate the vehicle yaw stability. The lateral error and heading angle error of each axis in the vehicle driving process were defined. A vehicle yaw motion controller was designed based on the sliding mode control (SMC) algorithm, the expected yaw rate was calculated, and the stability proof and steady state error analysis were carried out. The proportional integral (PI) controller was used to calculate the yaw moment of the vehicle body distributed to each drive shaft, and simulation and test were conducted on the U-shaped curve path. Research results show that the hydraulic rod stiffness is directly related to the vehicle speed and the front wheel angle when the vehicle turns in a steady state, and in any case, the front hydraulic rod stiffness of the connection module must be greater than the rear hydraulic rod stiffness. When the vehicle speed is about 22 km·h^-1, the optimal hydraulic rod stiffness is the smallest. When the vehicle speed is greater than 22 km·h^-1, as the speed increases, the optimal hydraulic rod stiffness rises, and the change rate of the front hydraulic rod stiffness is significantly greater than that of the rear hydraulic rod stiffness. When the speed is less than 22 km·h^-1, as the speed gets smaller, the optimal hydraulic rod stiffness becomes greater. The lateral error of the axle on the straight section is less than 0.03 m, and the heading angle error is less than 0.03 rad. The lateral error of the axle on the curve section is less than 0.06 m, and the heading angle error is less than 0.06 rad. In the driving process, the yaw rate of the vehicle body can quickly track the given value, and the driving stability of the vehicle improves, which verifies the effectiveness of the control strategy.More>

2023, 23(2): 240-250. doi: 10.19818/j.cnki.1671-1637.2023.02.017

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Sliding mode active disturbance rejection adhesion control method of high-speed train

LI Zhong-qi, HUANG Lin-jing, ZHOU Liang, YANG Hui, TANG Bo-wei

Abstract: In order to solve the problems of idling or sliding due to the change of rail surface during the operation of high-speed train so that train did not reach the maximum adhesive utilization, a sliding mode active disturbance rejection controller (SM-ADRC) of adhesion based on the maximum adhesion coefficient was designed. Considering the complex, time-varying and nonlinear characteristics of wheel-rail adhesion, a mechanical model of wheel-rail traction system was established based on the analysis of adhesion mechanism. The maximum likelihood estimation (MLE) method was used to identify the relevant parameters of different rail surfaces, and the maximum adhesion coefficient of the current rail surface was calculated to ensure that the train could always achieve the maximum adhesion utilization. The nonlinear error feedback control law in the active disturbance rejection control (ADRC) was improved by introducing the sliding mode algorithm, a SM-ADRC algorithm of adhesion was designed, the Levant tracking differentiator was used to reduce the initial tracking error, and the extended state observer (ESO) was used to estimate and compensate the total external disturbance of the system. The robustness of the system was improved by the sliding mode control. The CRH380A high-speed train was simulated by the MATLAB software. When the rail surface condition changed, the SM-ADRC of adhesion controlled the train to track the set speed, and was compared with the proportional-integral-differential (PID) controller, sliding mode controller and ADRC in the simulation results. Simulation results show that the maximum adhesion coefficient of the dry rail surface is 0.160, and the true value is identified at 16 s. The maximum adhesion coefficient of the wet rail surface is 0.106, and the true value is identified at 18 s. The speed tracking error range of the ADRC is within ±1 km·h^-1, and the speed tracking error fluctuates greatly after the rail surface changes. The speed tracking error range of the SM-ADRC of adhesion is within ±0.4 km·h^-1. After the rail surface changes, the speed tracking error fluctuates less, and the speed is more smooth and stable. The speed control tracking accuracy is higher than PID and sliding mode control methods. It can be seen that the proposed SM-ADRC of adhesion can realize the fast adhesion control of the train and achieve the maximum adhesion utilization.More>

2023, 23(2): 251-263. doi: 10.19818/j.cnki.1671-1637.2023.02.018

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Sliding mode periodic adaptive learning control method for medium-speed maglev trains

ZHANG Wen-jing, RUAN Yu-xin, GAO Ya-ping, CHEN Yu-feng, YUE Qiang, XU Hong-ze

Abstract: In order to improve the operation control performance of the medium-speed maglev train, the periodic characteristic of the train running along a fixed line was considered, and an operation control algorithm based on the sliding mode periodic adaptive learning control (SMPALC) method for the train was proposed. The corresponding sliding mode periodic adaptive controller was composed of the equivalent proportional-integral-differential (PID) and speed feedforward control part, the magnetic resistance and air resistance compensation part, and the ramp resistance sliding mode periodic adaptive compensation part. The operation controller parameters were tuned through the particle swarm optimization (PSO) algorithm. The sliding mode periodic adaptive controller was used to learn the train operation information in the previous period, the ramp resistance during train operation in real time was estimated and compensated, and the influence of ramp resistance on the train operation performance was eliminated. The semi-physical simulation test line of a medium-speed maglev train with a total route length of 5 076 m was numerically simulated, and the designed sliding mode periodic adaptive controller was compared with the PID controller through the simulation. Simulation results show that the maximum position tracking errors under the sliding mode periodic adaptive controller and PID controller are 0.004 and 0.007 m, respectively, and the maximum speed tracking errors are 0.007 and 0.036 m·s^-1, respectively. After four iterative periods, the sliding mode periodic adaptive controller has accurately estimated the given ramp resistance. When the control system is disturbed, the position and speed tracking curves under the sliding mode periodic adaptive controller and PID controller both fluctuate. However, compared with those under the PID controller, the tracking curves under the sliding mode periodic adaptive controller have a smaller fluctuation. Therefore, the proposed SMPALC method can improve the operation control performance of medium-speed maglev trains.More>

2023, 23(2): 264-272. doi: 10.19818/j.cnki.1671-1637.2023.02.019

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Stability model verification and control strategy optimization of train platoon based on stochastic priced timed game

LU Wan-li, LYU Ji-dong, GAO Jin-jin, CHAI Ming, LIU Hong-jie, TANG Tao, LI Dan-yong, SONG Dong-liang

Abstract: In order to ensure the safe operation of the train platoon and improve the platoon stability, the problems of stability model verification and control strategy optimization of the train platoon were studied. The train platoon based on train-train communication adopted three control strategies including constant distance interval, constant time interval, and variable time interval. A platoon control model consisting of a leader train and following trains was established by using the stochastic priced timed game(SPTG) automata, and the stability of the platoon model was analyzed. Under the premise of ensuring the safety of train operation, the relative position difference, relative speed difference, and time interval difference of the trains were taken as the cost function, and a control strategy set was obtained by the SPTG automata model of the platoon. The optimal driving strategy of the platoon was obtained by the Q-Learning method, and the safety and stability of the platoon operation were verified. In addition, the train operation tracking scenario was utilized to analyze the stability of the platoon. Simulation results show that through formal verification, the safety of the train platoon under the three control strategies is guaranteed. For SPTG theory, covariance optimization control, and Q-Learning method compared with PID control, the maximum errors of platoon stability under the constant distance interval strategy reduce to 0.19%, 0.18% and 0.11%, respectively, the maximum errors of platoon stability under the constant time interval strategy reduce to 30.21%, 10.34%, and 9.24%, respectively, and the maximum errors of platoon stability under the variable time interval strategy are 118.37%, 56.12%, and 39.80%, respectively. Therefore, the SPTG theory using the Q-Learning method can improve the stability of the train platoon under the premise of safety.More>

2023, 23(2): 273-286. doi: 10.19818/j.cnki.1671-1637.2023.02.020

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Lane-change risk warning in interweaving area considering information from intelligent connected near-neighboring vehicles

XIE Ji-ming, XIA Yu-lan, QIAN Zheng-fu, LIU Bing, QIN Ya-qin

Abstract: In view of the problems of large feature differences, unbalanced samples, and long parameter tuning time in predicting the lane-change risk of vehicles, the high-precision microscopic vehicle trajectory data were combined with the hyperparametric optimization machine learning method, and a method for identifying and warning of the lane-change risk in interweaving areas was proposed, which could be applied to intelligent connected vehicles (ICV). According to the unmanned aerial vehicle video, lane-change trajectories with time accuracy of 0.1 s and spatial accuracy of 0.1 m per pixel in the urban expressway interweaving area were extracted from a wide-area view, and the lane-change risk perception information, such as the vehicle spacing, vector velocity, acceleration, proximity rate, and velocity angle, was measured. A lane-change time-to-collision (TTC) model that took into account information from near-neighboring vehicles was introduced, and the urgent need for vehicles to merge into or leave arteries was reflected. In addition, the difference in the lane-change behaviors at different locations was described. The 15th quartile method and the interquartile range method were used, and the warning levels for lane-change risks were classified. With several evaluation metrics, such as the accuracy, true positive rate, and sensitivity, the linear classifier, support vector machine, K-nearest neighbor, and RUSBoost model were selected and compared in terms of the lane-change risk prediction results, and the optimal model for the real-time warning of lane-change risks in interweaving areas was selected. For the optimal model, the hyperparameters were optimized and validated. Research results show that the RUSBoost model is the optimal model. When the hyperparametric optimization machine learning method iterates 24th times, the minimum error and optimal point hyperparameter of RUSBoost appear, and the prediction accuracies of RUSBoost and optimized BRUSBoost models are 91.40% and 99.80%, respectively. The AUC values are 0.96 and 0.99, respectively, and the warning accuracy of the optimized BRUSBoost model for level Ⅰ and Ⅲ lane change risks improves by 50.9% and 41.2%, respectively. As a result, the defects of more complex and less predictable lane-change conditions of extreme risks improves effectively. The research results can help the ICV lane-change decisions and trajectory optimization and guide traffic management departments to develop ICV dynamic warning schemes.More>

2023, 23(2): 287-300. doi: 10.19818/j.cnki.1671-1637.2023.02.021

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