关键词：
Circulating fluidized bed fly ash;Ground granulated blast-furnace slag;Grout materials;Geopolymers;Performance;Microstructure
摘要：
Circulating fluidized bed fly ash (CFBFA) is a significant byproduct of power plants and has attracted considerable attention due to its potential as a low-cost geopolymer precursor. However, unstable components in CFBFA, such as sulfur trioxide (SO 3 ) and free lime (f-CaO), can lead to volumetric expansion, which limits its widespread application in cementitious materials. To address this issue, this study effectively combines CFBFA with ground granulated blast furnace slag (GGBS) to develop an environmentally friendly micro-expansive geopolymer subgrade grouting material. This approach enhances the utilization of CFBFA in cementitious applications. The research demonstrates that the utilization rate of CFBFA in the geopolymer grouting material can reach 70 %, and the material meets the subgrade grouting specifications for fluidity, setting time, and compressive strength. The developed grout material exhibits micro-expansive behavior that significantly improves repaired subgrade performance. Furthermore, freeze-thaw cycle test results confirm the durability of the grouting material, indicating that micro-expansion has a negligible effect on its durability. Additionally, X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) analyses were conducted to investigate the composition and microstructure of the grouting material with varying CFBFA dosages. These analyses reveal the performance evolution mechanisms of the grouting material, providing valuable insights into its preparation. Based on the experimental results, it is recommended to use a CFBFA content of 65–70 %, a GGBS content of 30–35 %, a 1.0 M alkaline activator at 35 % dosage, and a water-to-solid ratio of 0.65 to prepare high-performance subgrade grouting materials with micro-expansive properties and excellent durability. Therefore, this paper introduces a novel method for producing geopolymer subgrade grouting materials using CFBFA and GGBS, offering a new perspective on the wide application of CFBFA in cementitious materials and contributing to the reduction of its environmental impact.
Circulating fluidized bed fly ash (CFBFA) is a significant byproduct of power plants and has attracted considerable attention due to its potential as a low-cost geopolymer precursor. However, unstable components in CFBFA, such as sulfur trioxide (SO 3 ) and free lime (f-CaO), can lead to volumetric expansion, which limits its widespread application in cementitious materials. To address this issue, this study effectively combines CFBFA with ground granulated blast furnace slag (GGBS) to develop an environmentally friendly micro-expansive geopolymer subgrade grouting material. This approach enhances the utilization of CFBFA in cementitious applications. The research demonstrates that the utilization rate of CFBFA in the geopolymer grouting material can reach 70 %, and the material meets the subgrade grouting specifications for fluidity, setting time, and compressive strength. The developed grout material exhibits micro-expansive behavior that significantly improves repaired subgrade performance. Furthermore, freeze-thaw cycle test results confirm the durability of the grouting material, indicating that micro-expansion has a negligible effect on its durability. Additionally, X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) analyses were conducted to investigate the composition and microstructure of the grouting material with varying CFBFA dosages. These analyses reveal the performance evolution mechanisms of the grouting material, providing valuable insights into its preparation. Based on the experimental results, it is recommended to use a CFBFA content of 65–70 %, a GGBS content of 30–35 %, a 1.0 M alkaline activator at 35 % dosage, and a water-to-solid ratio of 0.65 to prepare high-performance subgrade grouting materials with micro-expansive properties and excellent durability. Therefore, this paper introduces a novel method for producing geopolymer subgrade grouting materials using CFBFA and GGBS, offering a new perspective on the wide application of CFBFA in cementitious materials and contributing to the reduction of its environmental impact.
摘要：
Thin-layer covers easily crack under traffic load, shortening their service life. Incorporating fiber materials into the mix can enhance crack resistance thanks to their abundance, affordability, and flexibility. However, different types of fibers have different performances in bitumen and mixtures due to different material properties. To explore this problem, basalt fiber, polypropylene fiber, and glass fiber were selected in this paper. The surface characteristics, internal structure, and adsorption capacity of oily substances were observed via scanning electron microscopy and oil absorption rate testing. The effects of fibers on the high-temperature and low-temperature properties of styrene-butadiene-styrene block copolymer-modified bitumen were investigated using the dynamic shear rheometer and the force ductility method. Ultimately, through indirect tensile testing and semi-circular bending tests, and the introduction of the toughness index and fracture toughness, a comprehensive evaluation was conducted on how varying fiber types and content affect the crack resistance and toughness of bitumen mixtures. The results show that the density and dispersion of the bundle fibers are the key to the oil absorption capacity under similar internal and external structural conditions. The oil absorption rate of polypropylene fiber is the best, reaching 5.423. Fiber incorporation can significantly improve the high-temperature rheological properties of bitumen. At 4% dosage, G*/sinδ increased by about 107.04% on average at 76 °C. At low temperatures, the increase in fiber content leads to a decrease in bitumen elasticity, and the influence of glass fiber is more obvious. The area of toughness did not reach 2000 N·mm at 4% dosage. After adding fibers, the toughness index and fracture toughness of the mixture increased by more than 2% and 35%, respectively. The maximum increases in fracture energy and crack initiation energy of the mixture are 14.29% and 47.29%, respectively. It shows that the fiber enhances the toughness, crack resistance, and crack propagation resistance of the mixture. The research results can provide some reference for the application of fiber-reinforced bitumen mixtures.
摘要：
In order to investigate the influence of the coexistence of clay and silt on the compression characteristics of sand, one-dimensional compression consolidation tests were carried out on reconstituted saturated sand-silt-clay mixtures with a constant initial void ratio, and the effects of fines content (FC) and clay-silt ratio (CS) on the compression characteristics of mixed soils were studied. The mechanism of the experimental results was additionally explained from a microscopic perspective. The test results show that: the compressibility of mixed soil increased with the increase in FC; the compressibility change rule of mixed soils with different CS is consistent under the same FC; the influence of CS on the e-lgp (the void ratio (e) versus logarithm of the pressure (p)) curve of mixed soil is inconsistent when FC is different: when FC = 3%, the compressibility of mixed soil decreased with the increase in CS; when FC = 7% and 10%, the compressibility of mixed soil gradually increased with the increase in CS; when FC = 5%, the compressibility of mixed soil did not show an obvious changing law with the increase in CS, and the compressibility of the specimen with FC = 5%-CS = 1 (FC = 5%, CS = 1) was the largest; when CS was same, the difference between e-lgp curves of mixed soil with different FC increased with the increase in CS. The compression model of sand-silt-clay mixtures was established, which can consider the effects of FC and CS. The reliability and applicability of the proposed model were verified by combining the experimental results of this paper and the test data of sand-clay mixture and sand-silt mixture in other literature.
通讯机构：
[Zhou, CJ ] G;Guangzhou Univ, Sch Civil Engn & Transportat, Guangzhou 510006, Peoples R China.
关键词：
urban rail transit ridership;land use;temporal heterogeneity;panel data analysis;transit-oriented development
摘要：
Understanding how land use affects urban rail transit (URT) ridership is essential for facilitating URT usage. While previous studies have explored the way that land use impacts URT ridership, few have figured out how this impact evolves over time. Utilizing URT turnstile and land use data in Beijing, we employed panel data analysis methods to verify the existence of the temporal heterogeneity of the impact and capture this temporal heterogeneity. The results identified time-varying impacts of land use on the URT boarding and alighting trips on weekdays and non-weekdays and also demonstrated the rationality of the mixed effects time-varying coefficient panel data (TVC-P) model in capturing this temporal heterogeneity accurately. The TVC-P model revealed how land use density appealed to URT commuting during weekday morning peak times, and how it triggered the generation of URT commutes during the weekday evening rush hours. The land use diversity promoted URT trips over an extended period on non-weekdays. Additionally, the study identified the time-varying impacts of specific land use on URT ridership. These insights provide both theoretical and empirical support for developing policies and actions that improve the efficiency of transportation systems and foster alignment between land use and transport.
摘要：
This paper proposes a novel hierarchical controller for connected truck platoons. To this end, the predecessor following topology is used to characterize the communication connectivity between connected trucks. Then, a longitudinal efficient controller consisting of upper-level and lower-level controllers is proposed. In particular, the upper-level controller is designed based on the kinematic model to handle the car-following interactions between connected trucks and delays in communication and input. The lower-level controller comprises a feedforward and a feedback control law. The feedforward control law converts the desired acceleration from the upper-level controller into the vehicle throttle or braking pressure using the inverse dynamic model, while the feedback control law compensates for the control error caused by unknown vehicle parameters. In addition, in the linear region, the internal stability is analyzed based on the second-order kinematic model using s-domain analysis and linearization method, respectively. Then, the string stability is proved. The influence of parameters on the stability performance is extensively discussed using the stability diagram. Finally, the feasibility of the proposed controller is verified via co-simulations in PreScan and TruckSim, in terms of acceleration, velocity, and spacing error profiles.
摘要：
Currently, isocyanate modified asphalt (IMA) has gradually attracted attention in the pavement field due to its good mechanical properties and environmental benefits. However, there also exists some challenges, such as high viscosity and poor low-temperature performance, for its further application. In this study, an environmental-friendly potential solving method is proposed by employing waste engine oil (WEO) as a co-modifier with polyaryl polymethylene isocyanate (PAPI). And the effect and modification mechanism of WEO and PAPI on neat asphalt are studied. Specifically, the optimal compositions of PAPI/WEO modified asphalt (PWMA) were firstly determined by learning the effects of the PAPI and WEO amounts on the viscosity, high- and low- temperature performance of neat asphalt. Then, the traditional physical properties, storage stability and aging resistance of PWMA and SBS modified asphalt (SBSMA) were analyzed and compared. Finally, the performance improvement mechanism of PWMA was detected by microscopic analyses. The result shows that adopting WEO as a kind of co-modifier can prepare excellent performance modified asphalt with PAPI. The prepared PWMA qualifies similar viscosity and high- and low- temperature performance to SBSMA, while has the better storage stability and aging resistance. Microscopic test results reveal that in the PWMA, PAPI reacts chemically with the neat asphalt to generate carbamate or urea macromolecular products, while WEO mainly plays the role of adsorbent and filler. These findings are significant for guiding the performance regulation of IMA by the environmental-friendly method.
Currently, isocyanate modified asphalt (IMA) has gradually attracted attention in the pavement field due to its good mechanical properties and environmental benefits. However, there also exists some challenges, such as high viscosity and poor low-temperature performance, for its further application. In this study, an environmental-friendly potential solving method is proposed by employing waste engine oil (WEO) as a co-modifier with polyaryl polymethylene isocyanate (PAPI). And the effect and modification mechanism of WEO and PAPI on neat asphalt are studied. Specifically, the optimal compositions of PAPI/WEO modified asphalt (PWMA) were firstly determined by learning the effects of the PAPI and WEO amounts on the viscosity, high- and low- temperature performance of neat asphalt. Then, the traditional physical properties, storage stability and aging resistance of PWMA and SBS modified asphalt (SBSMA) were analyzed and compared. Finally, the performance improvement mechanism of PWMA was detected by microscopic analyses. The result shows that adopting WEO as a kind of co-modifier can prepare excellent performance modified asphalt with PAPI. The prepared PWMA qualifies similar viscosity and high- and low- temperature performance to SBSMA, while has the better storage stability and aging resistance. Microscopic test results reveal that in the PWMA, PAPI reacts chemically with the neat asphalt to generate carbamate or urea macromolecular products, while WEO mainly plays the role of adsorbent and filler. These findings are significant for guiding the performance regulation of IMA by the environmental-friendly method.
期刊：
Advances in Space Research,2025年 ISSN：0273-1177
通讯作者：
Qing Xia
作者机构：
[Qiong Zheng; Huangteng Zhu; Qing Xia; Zixiao Guo; Lihong Zhu] Engineering Laboratory of Spatial Information Technology of Highway Geological Disaster Early Warning in Hunan Province, Changsha University of Science and Technology, Changsha, China
通讯机构：
[Qing Xia] E;Engineering Laboratory of Spatial Information Technology of Highway Geological Disaster Early Warning in Hunan Province, Changsha University of Science and Technology, Changsha, China
摘要：
Ensuring that land use efficiency and urbanization are in harmony has emerged as a critical concern requiring immediate attention to achieve sustainable urbanization in China. Taking the Chang-Zhu-Tan urban agglomeration (CZTUA) as an example, this study establishes an evaluation index system of land use efficiency and urbanization using multi-source remote sensing data in 2020 and analyzes the coupling coordination degree (CCD) between these factors. Furthermore, the standardization methods and exploratory spatial data analysis method are combined to investigate the spatial correlation of the CCD among land use efficiency and urbanization. The study shows that: (1) In CZTUA, there is a positive correlation between land use efficiency and urbanization and this promotes urbanization. (2) The overall coupling degree in the CZTUA is in the running-in level and most districts are at the elementary or middle rank coordinated levels. (3) The spatial clustering characteristics have the “center-periphery” pattern, with the further away from the core city, the lower the level of coupling coordination becomes. (4) From the perspective of geographical association, the High-High agglomeration, mainly located in Changsha City, showed higher development levels compared to surrounding areas. Development gradually diminished as one moves outward, forming a Low-High agglomeration. Low-Low agglomeration was represented by You, Chaling and Yanling districts. The methodology used in this study is relevant for promoting urbanization and improving land use efficiency in Chinese city clusters.
Ensuring that land use efficiency and urbanization are in harmony has emerged as a critical concern requiring immediate attention to achieve sustainable urbanization in China. Taking the Chang-Zhu-Tan urban agglomeration (CZTUA) as an example, this study establishes an evaluation index system of land use efficiency and urbanization using multi-source remote sensing data in 2020 and analyzes the coupling coordination degree (CCD) between these factors. Furthermore, the standardization methods and exploratory spatial data analysis method are combined to investigate the spatial correlation of the CCD among land use efficiency and urbanization. The study shows that: (1) In CZTUA, there is a positive correlation between land use efficiency and urbanization and this promotes urbanization. (2) The overall coupling degree in the CZTUA is in the running-in level and most districts are at the elementary or middle rank coordinated levels. (3) The spatial clustering characteristics have the “center-periphery” pattern, with the further away from the core city, the lower the level of coupling coordination becomes. (4) From the perspective of geographical association, the High-High agglomeration, mainly located in Changsha City, showed higher development levels compared to surrounding areas. Development gradually diminished as one moves outward, forming a Low-High agglomeration. Low-Low agglomeration was represented by You, Chaling and Yanling districts. The methodology used in this study is relevant for promoting urbanization and improving land use efficiency in Chinese city clusters.
摘要：
High-modulus asphalt mixtures are extensively employed in pavement engineering due to their exceptional resistance to high-temperature deformation. Nonetheless, fatigue failure remains a critical mode of degradation for these materials. This study aims to enhance the fatigue resistance design of high-modulus asphalt pavements by evaluating their fatigue damage behavior under varying conditions, specifically different maximum nominal particle sizes (AC-13C and AC-20C) and aging durations (1, 3, 5, and 7 days). An empirical model was formulated to characterize the performance degradation of high-modulus asphalt mixtures during fatigue testing, and the corresponding decay patterns were systematically analyzed. The results demonstrate that the modulus decay behavior of high-modulus asphalt mixtures can be categorized into three distinct phases: migration, stability, and failure, as revealed by indirect tensile tests. The parameters m and n in the fatigue modulus decay model exhibited a positive correlation with aging time. Moreover, as aging progressed, the k parameter in the S-N fatigue equation decreased, while the n parameter increased. Both the initial and critical fatigue modulus values of the high-modulus asphalt mixtures showed a significant increase with aging. Specifically, the initial modulus ranged from 4500 MPa to 8500 MPa, while the critical modulus varied between 1000 MPa and 1800 MPa, depending on the aging period. These findings offer crucial insights for optimizing the fatigue-resistant design of high-modulus asphalt pavements.
High-modulus asphalt mixtures are extensively employed in pavement engineering due to their exceptional resistance to high-temperature deformation. Nonetheless, fatigue failure remains a critical mode of degradation for these materials. This study aims to enhance the fatigue resistance design of high-modulus asphalt pavements by evaluating their fatigue damage behavior under varying conditions, specifically different maximum nominal particle sizes (AC-13C and AC-20C) and aging durations (1, 3, 5, and 7 days). An empirical model was formulated to characterize the performance degradation of high-modulus asphalt mixtures during fatigue testing, and the corresponding decay patterns were systematically analyzed. The results demonstrate that the modulus decay behavior of high-modulus asphalt mixtures can be categorized into three distinct phases: migration, stability, and failure, as revealed by indirect tensile tests. The parameters m and n in the fatigue modulus decay model exhibited a positive correlation with aging time. Moreover, as aging progressed, the k parameter in the S-N fatigue equation decreased, while the n parameter increased. Both the initial and critical fatigue modulus values of the high-modulus asphalt mixtures showed a significant increase with aging. Specifically, the initial modulus ranged from 4500 MPa to 8500 MPa, while the critical modulus varied between 1000 MPa and 1800 MPa, depending on the aging period. These findings offer crucial insights for optimizing the fatigue-resistant design of high-modulus asphalt pavements.
作者机构：
[Shi, Liwan; Li, Xiongxin; Liang, Hehao] School of Transportation and Civil Engineering and Architecture, Foshan University, Foshan, Guangdong, China;[Guo, Hongjie] Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong, China;Foshan Road and Bridge Supervision Station Co., Ltd., Foshan, Guangdong 528041, China;Foshan Transportation Science and Technology Co., Ltd., Foshan, Guangdong 528041, China;[Zhou, Rong] Guangzhou Jishan Construction Technology Co., Ltd, Guangzhou, Guangdong, China
通讯机构：
[Hehao Liang] S;School of Transportation and Civil Engineering and Architecture, Foshan University, Foshan, Guangdong, China
作者：
Juan Xie*;Yan Zhou;Xucheng Zhao;Yuhang Jiang;Hao Huang;...
期刊：
Construction and Building Materials,2025年482:141728 ISSN：0950-0618
通讯作者：
Juan Xie
作者机构：
[Yan Zhou; Xucheng Zhao; Yuhang Jiang; Hao Huang] School of Transportation, Changsha University of Science and Technology, Changsha 410114, China;National Key Laboratory of Green and Long-Life Road Engineering in Extreme Environment (Changsha), Changsha University of Science and Technology, Changsha 410114, China;[Juan Xie; Qunshan Ye] School of Transportation, Changsha University of Science and Technology, Changsha 410114, China<&wdkj&>National Key Laboratory of Green and Long-Life Road Engineering in Extreme Environment (Changsha), Changsha University of Science and Technology, Changsha 410114, China
通讯机构：
[Juan Xie] S;School of Transportation, Changsha University of Science and Technology, Changsha 410114, China<&wdkj&>National Key Laboratory of Green and Long-Life Road Engineering in Extreme Environment (Changsha), Changsha University of Science and Technology, Changsha 410114, China
摘要：
The service performance of crumb rubber modified asphalt pavement will be negatively affected by the poor storage stability of crumb rubber modified asphalt (CRMA). Therefore, in this study, bio-desulfurized crumb rubber (BCR) was procured via the desulfurization effect of two types of microorganisms, after which bio-desulfurized crumb rubber modified asphalt (BCRMA) was fabricated. Meanwhile, a combined approach integrating macroscopic experiments and molecular dynamics (MD) simulation was utilized to investigate the storage stability of BCRMA. First and foremost, an organic element analyzer (EA) and a Fourier Transform Infrared Spectrometer (FTIR) were utilized to characterize the desulfurization state of crumb rubber (CR) subjected to different bio-desulfurization durations. Based on these findings, research on how bio-desulfurization treatment affects the storage stability of CRMA was conducted. Subsequently, CRMA models with varying degrees of desulfurization were established. The compatibility between BCR and base asphalt (BA) was then analyzed using parameters such as solubility parameters, mean squared displacement (MSD), diffusion coefficient (DC), free fraction volume (FFV), and glass transition temperature (T g ). This was done to further evaluate the storage stability of BCRMA. The results indicate that the bio-desulfurization treatment has a notable effect on boosting the storage stability of CRMA. Specifically, the segregation softening point differences of the modified asphalts subjected to bio-desulfurization for 7 days and 14 days are decreased by 29.1 % and 41.8 %, respectively. The molecular simulation results further validate this conclusion. In comparison with the non-desulfurized CR, the structural units of BCR and BA exhibit a smaller difference in interaction energy. Moreover, FFV and DC demonstrate that the diffusion capacity of BCR within BA is augmented, and its interaction with each component in the asphalt is strengthened as well. This situation is more favorable for the mutual dissolution of the two substances, thus strengthening the storage stability of BCRMA accordingly.
The service performance of crumb rubber modified asphalt pavement will be negatively affected by the poor storage stability of crumb rubber modified asphalt (CRMA). Therefore, in this study, bio-desulfurized crumb rubber (BCR) was procured via the desulfurization effect of two types of microorganisms, after which bio-desulfurized crumb rubber modified asphalt (BCRMA) was fabricated. Meanwhile, a combined approach integrating macroscopic experiments and molecular dynamics (MD) simulation was utilized to investigate the storage stability of BCRMA. First and foremost, an organic element analyzer (EA) and a Fourier Transform Infrared Spectrometer (FTIR) were utilized to characterize the desulfurization state of crumb rubber (CR) subjected to different bio-desulfurization durations. Based on these findings, research on how bio-desulfurization treatment affects the storage stability of CRMA was conducted. Subsequently, CRMA models with varying degrees of desulfurization were established. The compatibility between BCR and base asphalt (BA) was then analyzed using parameters such as solubility parameters, mean squared displacement (MSD), diffusion coefficient (DC), free fraction volume (FFV), and glass transition temperature (T g ). This was done to further evaluate the storage stability of BCRMA. The results indicate that the bio-desulfurization treatment has a notable effect on boosting the storage stability of CRMA. Specifically, the segregation softening point differences of the modified asphalts subjected to bio-desulfurization for 7 days and 14 days are decreased by 29.1 % and 41.8 %, respectively. The molecular simulation results further validate this conclusion. In comparison with the non-desulfurized CR, the structural units of BCR and BA exhibit a smaller difference in interaction energy. Moreover, FFV and DC demonstrate that the diffusion capacity of BCR within BA is augmented, and its interaction with each component in the asphalt is strengthened as well. This situation is more favorable for the mutual dissolution of the two substances, thus strengthening the storage stability of BCRMA accordingly.
期刊：
SAE International Journal of Connected and Automated Vehicles,2025年9(1):1-16 ISSN：2574-0741
作者机构：
[Zhaolei Zhang; Zhizhen Liu; Feng Tang] Changsha University of Science and Technology, China;[Xibin Ding] Changsha University of Science and Technology, School of Transportation Engineering, China
摘要：
The existing variable speed limit (VSL) control strategies rely on variable message signs, leading to slow response times and sensitivity to driver compliance. These methods struggle to adapt to environments where both connected automated vehicles (CAVs) and manual vehicles coexist. This article proposes a VSL control strategy using the deep deterministic policy gradient (DDPG) algorithm to optimize travel time, reduce collision risks, and minimize energy consumption. The algorithm leverages real-time traffic data and prior speed limits to generate new control actions. A reward function is designed within a DDPG-based actor-critic framework to determine optimal speed limits. The proposed strategy was tested in two scenarios and compared against no-control, rule-based control, and DDQN-based control methods. The simulation results indicate that the proposed control strategy outperforms existing approaches in terms of improving TTS (total time spent), enhancing the throughput efficiency of the bottleneck area, and reducing the spatial and temporal extent of traffic congestion. Compared to the suboptimal DDQN-based VSL control, the proposed strategy improves TTS by 9.3% in Scenario 1 and by 11% in Scenario 2. The sensitivity analysis shows that the proposed control strategy improves performance as the penetration rate of CAVs increases. However, when the penetration rate reaches a certain threshold, the potential for further optimization becomes limited. Furthermore, higher time-to-collision (TTC) values, influenced by the reward function r 2, enhance traffic safety.
摘要：
As an emerging environmentally friendly solid waste-based composite foam lightweight soil, saponified slag fly ash (SS-FA) foam lightweight soil has a wide range of application prospects in road engineering. In this paper, the dynamic characteristics of SS-FA foam light soil material were investigated. Dynamic triaxial tests under different cyclic loading conditions were designed to analyze the variation rules of dynamic elastic modulus and damping ratio. The results showed that the stress-strain curve of SS-FA foam lightweight soil can be divided into three stages: elastic stage, plateau stage, and stress yielding stage. Under cyclic dynamic load, with the increase of dynamic stress amplitude, the dynamic elastic modulus of 400–700 kg/m3 samples gradually increased to the maximum, reaching 235.24 MPa, 324.54 MPa, 356.45 MPa, 379.67 MPa, respectively. The damping ratio, on the other hand, shows a tendency to first decrease and then slowly increase to stabilize. The dynamic elastic modulus is positively correlated with density grade, confining pressure and loading frequency. The damping ratio decreases with the increase of density grade and loading frequency, and increases with the increase of confining pressure. The electron microscope test was designed and image processing and data statistics were carried out. Through the grey correlation analysis, the correlation degree between the microstructure parameters of SS-FA foamed lightweight soil and the macroscopic mechanical properties is basically above 0.6, indicating that the two have a significant correlation. A normalized prediction formula model between the dynamic elastic modulus of materials and the conditional parameters was established. The R 2 of the linear fitting of the predicted value is 0.964, indicating that the prediction model has a high degree of fitting and a good prediction effect. The research results revealed the dynamic mechanical properties of foamed lightweight soil, and provided a reference for the application of SS-FA foamed lightweight soil in subgrade engineering.
As an emerging environmentally friendly solid waste-based composite foam lightweight soil, saponified slag fly ash (SS-FA) foam lightweight soil has a wide range of application prospects in road engineering. In this paper, the dynamic characteristics of SS-FA foam light soil material were investigated. Dynamic triaxial tests under different cyclic loading conditions were designed to analyze the variation rules of dynamic elastic modulus and damping ratio. The results showed that the stress-strain curve of SS-FA foam lightweight soil can be divided into three stages: elastic stage, plateau stage, and stress yielding stage. Under cyclic dynamic load, with the increase of dynamic stress amplitude, the dynamic elastic modulus of 400–700 kg/m3 samples gradually increased to the maximum, reaching 235.24 MPa, 324.54 MPa, 356.45 MPa, 379.67 MPa, respectively. The damping ratio, on the other hand, shows a tendency to first decrease and then slowly increase to stabilize. The dynamic elastic modulus is positively correlated with density grade, confining pressure and loading frequency. The damping ratio decreases with the increase of density grade and loading frequency, and increases with the increase of confining pressure. The electron microscope test was designed and image processing and data statistics were carried out. Through the grey correlation analysis, the correlation degree between the microstructure parameters of SS-FA foamed lightweight soil and the macroscopic mechanical properties is basically above 0.6, indicating that the two have a significant correlation. A normalized prediction formula model between the dynamic elastic modulus of materials and the conditional parameters was established. The R 2 of the linear fitting of the predicted value is 0.964, indicating that the prediction model has a high degree of fitting and a good prediction effect. The research results revealed the dynamic mechanical properties of foamed lightweight soil, and provided a reference for the application of SS-FA foamed lightweight soil in subgrade engineering.
关键词：
infrastructure;roadway design;performance effects of geometric design AKD10;curves;safety;safety performance and analysis;Bayesian methods
摘要：
The safety performance of horizontal and crest vertical curve combinations (also named as crest combinations or crest combined curves) is substantially associated with their geometric design. To evaluate their safety performance accurately, three Bayesian hierarchical negative binomial (NB) models with various structures of temporal correlation (including linear time trend, quadratic time trend, and autoregressive-1) are proposed for building a relationship between crash frequency and the separated and combined geometric design attributes of crest combination on freeways. An 8 year (2011-2018) crash dataset of 124 crest combination sections on four freeways in Washington state is collected and used for the model development and comparison. The results of model assessment indicate that the hierarchical NB model with autoregressive-1 is clearly superior to other alternatives. The parameter estimation results in the model reveal that in addition to the crash exposure variables (i.e., section length and annual average daily traffic), four geometric design attributes (vertical curvature, horizontal curvature, approach grade, and overlapping proportion) and two roadway configuration characteristics (lane width and left shoulder width) have significant effects on the safety performance. Considerable over-dispersion, cross-group heterogeneity, and temporal correlation are also found in the best-performing model. According to the results, some strategies for highway design are proposed to improve the safety performance of freeway crest combinations.
摘要：
As an essential component of China's comprehensive transportation network, freeways play an irreplaceable role in promoting regional economic integration, improving logistics efficiency, and serving public travel. However, the development of freeways faces challenges such as the underutilization of road resources, significant financial pressure for construction and maintenance, and imbalanced revenue and expenditure leading to heavy debt burdens, which severely impact the sustainable development of freeways. Optimizing freeway toll rates is an effective measure to alleviate these issues, playing a crucial role in enhancing the operational efficiency of the road network and increasing the revenue of freeway operating enterprises. Existing studies have focused on finding the optimal toll rates for freeways based on bi-level programming models, neglecting the dynamic relationships among individual travel behavior preferences, toll rates, travel demand, and toll revenue. Grounded in bounded rationality theory, the research employs microscopic traffic simulation technology to analyze the dynamic relationships among freeway toll rates, travel demand, and toll revenue. The results confirm that travel demand decreases as toll rates increase, while toll revenue exhibits asymmetric "synchronization" and "asynchronization" phases, peaking at CYN 58.9 thousand (USD 8246) when the toll rate reaches CYN 0.45/km (USD 0.06/km). Additionally, users' rationality levels significantly affect the stabilization time of toll revenue, and the speed difference between freeways and parallel roads demonstrates a threshold effect on travel demand and revenue. These findings provide theoretical and technical support for optimizing freeway toll strategies, enhancing operational efficiency, and promoting sustainable transportation development.
关键词：
transient infiltration;unsaturated soil;Rankine earth pressure;shear strength envelope shell;infiltration transitoire;sol non saturé;pression de terre selon Rankine;coque enveloppante de la résistance au cisaillement
摘要：
To investigate the spatiotemporal effect of transient rainfall infiltration on the earth pressures, a novel solution scheme is proposed by integrating transient seepage and the envelope shell model of unsaturated shear strength. The acquisition method of equivalent parameters (i.e., cohesion and friction angle) is put forward, presenting the nonlinearity of shear strength in both two dimensions: net normal stress and matric suction. Moreover, Iverson model is modified to depict the general initial distribution of pressure head and the post-rainfall dissipation by introducing the Gaussian function and the recession coefficient. Finally, the nonlinear Rankine earth pressure characteristics are captured by linking the matric suction, mass density, and the shear strength parameters in a self-consistent fashion. Case validation and parametric analysis show good adaptability of the proposed model in calculating the unsaturated earth pressure with depicting the subtle and overlooked effect of soil unit weight during water infiltration. Thus, it contributes to evaluating the influence of transient infiltration on the performance of retaining structures under rainfall conditions.
摘要：
The dry process modification is characterized by simplicity, flexibility, low energy consumption, and low pollution, making it an ideal choice in pavement repair engineering. This study aims to optimize the use of waste rubber powder and SBS modifiers in dry process composite modification by preparing dry process WR/SBS composite modified particles (WR/SBS CMP) using a twin-screw extruder. The optimum mixing content of modified particles was determined through comparative analysis of pavement performance of dry process WR/SBS composite modified, wet-process SBS-modified, and matrix asphalt mixtures. The rheological properties and modification mechanism of the asphalt binder extracted from these mixtures were tested and analyzed. The results indicate that when the content of dry process WR/SBS CMP is 2.3% of the aggregate weight in the mixture, the comprehensive pavement performance of the dry process composite-modified asphalt mixture is optimal. Melt extrusion granulation at high temperatures, along with the addition of additives such as naphthenic and aromatic oils, promoted the degradation and refinement of the rubber powder and SBS, improving their compatibility and dispersion within the asphalt binder. The modified particles uniformly interact with the asphalt binder, increasing the proportion of elastic components, reducing stress sensitivity, and enhancing performance at both high and low temperatures, and fatigue resistance. Fourier Transform Infrared Spectroscopy (FTIR) confirmed that the modification mechanism was a physical modification. This research promotes the broad application of waste rubber powder and dry process modification in asphalt mixtures, offering significant economic and social benefits.
The dry process modification is characterized by simplicity, flexibility, low energy consumption, and low pollution, making it an ideal choice in pavement repair engineering. This study aims to optimize the use of waste rubber powder and SBS modifiers in dry process composite modification by preparing dry process WR/SBS composite modified particles (WR/SBS CMP) using a twin-screw extruder. The optimum mixing content of modified particles was determined through comparative analysis of pavement performance of dry process WR/SBS composite modified, wet-process SBS-modified, and matrix asphalt mixtures. The rheological properties and modification mechanism of the asphalt binder extracted from these mixtures were tested and analyzed. The results indicate that when the content of dry process WR/SBS CMP is 2.3% of the aggregate weight in the mixture, the comprehensive pavement performance of the dry process composite-modified asphalt mixture is optimal. Melt extrusion granulation at high temperatures, along with the addition of additives such as naphthenic and aromatic oils, promoted the degradation and refinement of the rubber powder and SBS, improving their compatibility and dispersion within the asphalt binder. The modified particles uniformly interact with the asphalt binder, increasing the proportion of elastic components, reducing stress sensitivity, and enhancing performance at both high and low temperatures, and fatigue resistance. Fourier Transform Infrared Spectroscopy (FTIR) confirmed that the modification mechanism was a physical modification. This research promotes the broad application of waste rubber powder and dry process modification in asphalt mixtures, offering significant economic and social benefits.
摘要：
In this paper, the effects of polyvinyl alcohol fiber incorporation on the crack resistance of low-dose cement-stabilized crushed stone have been investigated. The resulting change in the compressive strength, compressive rebound modulus, splitting strength, dry shrinkage factor, and impact toughness with fiber incorporation was evaluated through the unconfined compressive strength test, compressive rebound modulus test, crack strength test, dry shrinkage test, and impact toughness test. The results showed the positive influence of PVA fibers on the crack resistance of low-dose cement-stabilized crushed stone. PVA fibers have been shown to improve the compressive strength, splitting strength, and impact toughness of low-dose cement-stabilized crushed stone while reducing the compressive rebound modulus and dry shrinkage factor. With the increase of fiber incorporation, the compressive strength, splitting strength, and impact toughness tend to increase first and then decrease. The compressive resilience modulus and dry shrinkage coefficient showed a tendency to decrease first and then increase. When the fiber dosage is 0.9 kg/m3, the maximum energy consumed in the fracture of the specimen, the strongest impact resistance and impact ductility of the material, the indexes reach the optimal value, indicating that the crack resistance of PVA fiber low-dose cement-stabilized crushed stone is optimal at this dosage. This study provides a theoretical basis for promoting and applying PVA fiber in low-dose cement-stabilized gravel.
摘要：
Hot mix asphalt mixture is considered the ideal approach to reuse waste plastics in high-value applications because of its very high amount of usage in highway construction. However, the differences in polarity and density between polymers and asphalt lead to polymer coalescence and therefore the poor storage stability of modified asphalt. These challenges are exalted when recycling commingled plastics. This study introduced an innovative compatibilization strategy and mechanism for co-stabilizing commingled plastics and pyrolyzed rubber in asphalt. Commingled plastics were first grafted with maleic anhydride for surface activation, followed by reactive kneading with pyrolyzed rubber and crosslinking agent to form an integrated thermoplastic elastomer (ITPE) for asphalt modification. The mechanical, thermal, and interfacial behaviors of the ITPE were evaluated through tensile testing, thermogravimetric analysis, and scanning electron microscopy. The storage stability and rheological properties of the modified binder blends were evaluated through the cigar tube test and dynamic shear rheometer testing. Results demonstrated a successful formation of imide bonds in the ITPE, which can improve the strength, ductility, and thermal stability of rubber-plastic composites. Appropriate utilization of crosslinking agents can improve both rutting and fatigue resistance of ITPE-modified asphalt with good storage stability because of the co-existence of rigid plastic and soft rubbery regimes and the formation of a crosslink network. However, excessive content of crosslinker led to severe phase separation and reduced storage stability of modified binder blends. Extra crosslinker tended to float in asphalt because of its low density and caused an excessive formation of the crosslink network in the top section of the asphalt.
摘要：
The occurrence of top-down (TD) cracking has gradually become a prevalent issue in semi-rigid base asphalt pavements after prolonged service. A coupled simulation model integrating the finite difference method (FDM) and discrete element method (DEM) was employed to investigate the mechanical behavior of asphalt pavement containing a pre-existing TD crack. The mesoscopic parameters of the model were calibrated based on the mixture modulus and the static mechanical response on the MLS66 test road. Finally, an analysis was performed to assess how variations in TD crack depth and longitudinal length affect the distribution patterns of transverse tensile stress, vertical shear stress, and vertical compressive stress. The results indicate that the vertical propagation of TD crack significantly increases both the tensile stress value and range on the middle surface, while the longitudinal development of TD crack has minimal impact. This phenomenon may result in more severe fatigue failure on the middle surface. With the vertical and longitudinal development of TD crack, the vertical shear stress and compressive stress show obvious "two-stage" characteristics. When the crack's vertical length reaches 40 mm, there is a sharp increase in stress on the upper surface. As the crack continues to propagate vertically, the growth of stress on the upper surface becomes negligible, while the stress in the middle and lower layers increased significantly. Conversely, for longitudinal development of TD crack, any changes in stress are insignificant when their length is less than 180 mm; however, as they continue to develop longitudinally beyond this threshold, there is a sharp increase in stress levels. These findings hold great significance for understanding pavement structure deterioration and maintenance behavior associated with TD crack.
The occurrence of top-down (TD) cracking has gradually become a prevalent issue in semi-rigid base asphalt pavements after prolonged service. A coupled simulation model integrating the finite difference method (FDM) and discrete element method (DEM) was employed to investigate the mechanical behavior of asphalt pavement containing a pre-existing TD crack. The mesoscopic parameters of the model were calibrated based on the mixture modulus and the static mechanical response on the MLS66 test road. Finally, an analysis was performed to assess how variations in TD crack depth and longitudinal length affect the distribution patterns of transverse tensile stress, vertical shear stress, and vertical compressive stress. The results indicate that the vertical propagation of TD crack significantly increases both the tensile stress value and range on the middle surface, while the longitudinal development of TD crack has minimal impact. This phenomenon may result in more severe fatigue failure on the middle surface. With the vertical and longitudinal development of TD crack, the vertical shear stress and compressive stress show obvious "two-stage" characteristics. When the crack's vertical length reaches 40 mm, there is a sharp increase in stress on the upper surface. As the crack continues to propagate vertically, the growth of stress on the upper surface becomes negligible, while the stress in the middle and lower layers increased significantly. Conversely, for longitudinal development of TD crack, any changes in stress are insignificant when their length is less than 180 mm; however, as they continue to develop longitudinally beyond this threshold, there is a sharp increase in stress levels. These findings hold great significance for understanding pavement structure deterioration and maintenance behavior associated with TD crack.
通讯机构：
[Hu, L ] S;Southwest Jiaotong Univ, Sch Transportat & Logist, Chengdu, Peoples R China.
关键词：
Carsharing services;Carbon emissions;Hybrid electric vehicles;Multiple-objective simulation-optimization;Pareto optimality;MGD-SPSA
摘要：
Hybrid electric vehicles (HEVs) are perceived as transitional products bridging the gap between fueled vehicles and electric vehicles (EVs) because people intuitively believe that EVs are more environmentally friendly than HEVs. But is this perception true in the context of carsharing services (CSSs)? This paper pioneers a general large-scale multi-objective simulation–optimization (MOSO) method to explore the values of deploying HEVs in CSSs. We firstly develop a physically logical simulation model, emulating operations of CSSs and capturing mesoscopic dynamics of shared vehicles in a link-based traffic network. This model adopts an event-driven discrete-event mechanism, enhancing efficiency while maintaining high fidelity. Subsequently, we design a simulation–optimization framework aimed at achieving Pareto optimality by jointly optimizing station capacity, fleet size, and trip pricing. The goal is twofold: to maximize operational profits and to minimize carbon emissions, thereby quantitatively analyzing the potential of shared HEVs (SHEVs). To tackle the high-dimensional MOSO problem, we introduce the multi-objective optimization into stochastic approximation field by proposing a general algorithm that incorporates the multiple gradient descent algorithm with the simultaneous perturbation stochastic approximation algorithm. Furthermore, we derive its analytical expression for bi-objective optimization problems. We theoretically prove and practically demonstrate its strong global convergence. The efficiency of this method was validated through large-scale computational experiments conducted in Chengdu, Sichuan Province, involving 66,710 decision variables. These experiments showcased the method’s superiority over existing MOSO algorithms. Several groups of sensitivity experiments focusing on vehicle types and traffic scenarios reveal some interesting findings. (1) Regardless of the increase in travel distances, SHEVs, which can be viewed as shared EVs (SEVs) without range anxiety (RA), continue to primarily rely on electricity rather than fuel for their operational mileages. This high utilization of electricity results in lower carbon emissions compared to SEVs. (2) Under any traffic condition, the dual-engine feature of SHEVs significantly reduces the number of failed pickups. (3) As travel demand increases, the state of charge for SEVs may rapidly fall below the threshold that triggers RA, whereas SHEVs maintain a more reliable power supply.
Hybrid electric vehicles (HEVs) are perceived as transitional products bridging the gap between fueled vehicles and electric vehicles (EVs) because people intuitively believe that EVs are more environmentally friendly than HEVs. But is this perception true in the context of carsharing services (CSSs)? This paper pioneers a general large-scale multi-objective simulation–optimization (MOSO) method to explore the values of deploying HEVs in CSSs. We firstly develop a physically logical simulation model, emulating operations of CSSs and capturing mesoscopic dynamics of shared vehicles in a link-based traffic network. This model adopts an event-driven discrete-event mechanism, enhancing efficiency while maintaining high fidelity. Subsequently, we design a simulation–optimization framework aimed at achieving Pareto optimality by jointly optimizing station capacity, fleet size, and trip pricing. The goal is twofold: to maximize operational profits and to minimize carbon emissions, thereby quantitatively analyzing the potential of shared HEVs (SHEVs). To tackle the high-dimensional MOSO problem, we introduce the multi-objective optimization into stochastic approximation field by proposing a general algorithm that incorporates the multiple gradient descent algorithm with the simultaneous perturbation stochastic approximation algorithm. Furthermore, we derive its analytical expression for bi-objective optimization problems. We theoretically prove and practically demonstrate its strong global convergence. The efficiency of this method was validated through large-scale computational experiments conducted in Chengdu, Sichuan Province, involving 66,710 decision variables. These experiments showcased the method’s superiority over existing MOSO algorithms. Several groups of sensitivity experiments focusing on vehicle types and traffic scenarios reveal some interesting findings. (1) Regardless of the increase in travel distances, SHEVs, which can be viewed as shared EVs (SEVs) without range anxiety (RA), continue to primarily rely on electricity rather than fuel for their operational mileages. This high utilization of electricity results in lower carbon emissions compared to SEVs. (2) Under any traffic condition, the dual-engine feature of SHEVs significantly reduces the number of failed pickups. (3) As travel demand increases, the state of charge for SEVs may rapidly fall below the threshold that triggers RA, whereas SHEVs maintain a more reliable power supply.
