摘要：
This study aimed to develop a method to determine nonlinear viscoelastic properties of subgrade soil using the light weight deflectometer (LWD) test. Firstly, a constitutive model was developed to accurately characterize the nonlinear viscoelastic behavior of subgrade soil. A User-Defined Material Subroutine (UMAT) was coded to define this constitutive model in ABAQUS, which was verified by the virtual triaxial test analysis. Secondly, a numerical model was developed to simulate the LWD test, which considered the true LWD load pattern and the constitutive nature of subgrade soil. The sensitivity analysis demonstrated that the viscoelastic parameters significantly affected the deflection-time history curves. Subsequently, a batch calculation program was developed via MATLAB and ABAQUS to automatically compute the dynamic responses of subgrade in the LWD test. A total of 42,057 groups of subgrade deflection data were calculated under the LWD load, covering a wide range of nonlinear viscoelastic parameters. Finally, two machine-learning approaches (i.e., artificial neural network [ANN] and convolutional neural network [CNN]) were proposed to backcalculate these viscoelastic parameters of soil from the LWD load–deflection-time history data. The results showed that the CNN approach was much more accurate than the ANN approach for the backcalculation of the nonlinear viscoelastic properties of subgrade.
摘要：
Internal erosion refers to the movement of fine particles within soil framework due to subsurface water seepage. Existing criteria for assessing internal erosion usually are based on static loading, and the effect of cyclic load is not considered. Additionally, there are limited studies to examine the particle -size distribution and origin of eroded fine particles. This study presents an experimental investigation that examines the impact of cyclic loading on internal stability through a series of seepage tests. The composition and origin of lost particles are quantitatively studied using particle staining and image recognition techniques. With increasing hydraulic gradient, particle erosion progresses from top layer to bottom layer, with a gradual increase in the maximum particle size of eroded particles from each layer. After significant loss of particles, the specimens reach a state of transient equilibrium, resulting in a gradual slowdown of both particle loss rate and average flow velocity. The results indicate that cyclic loading promotes massive particle loss and causes erosion failure of specimens that are considered stable according to existing criteria. The reason is that under cyclic loading, local hydraulic gradients is oscillating, and a larger than average hydraulic gradient may occur, which is responsible for the internal instability. The analysis suggests that existing criteria can provide a reasonable assessment of the relative stabilities of specimens under static loads but fail to capture the stabilities under cyclic loading conditions.
摘要：
Recycled rubber materials represent an environmentally sustainable option as asphalt modifiers. This research delves into the modification effects of Styrene Butadiene Rubber (SBR) asphalt at varying SBR content levels, employing a blend of molecular simulation techniques and laboratory experimentation. A comprehensive molecular model of SBR-modified asphalt is established, and molecular dynamics simulations are executed to scrutinize the thermodynamic attributes, dipole moments, mechanical characteristics, and adhesion properties inherent to SBR asphalt. The outcomes of this inquiry reveal that SBR exhibits notable compatibility with a majority of asphalt molecules, as evidenced by their dipole moments. The introduction of SBR into the asphalt matrix results in the adsorption of a substantial quantity of lightweight components, fostering the formation of a cross-linked network that bolsters the asphalt's resilience against external deformation forces. Furthermore, in terms of adhesion work, asphalt demonstrates heightened affinity with alkaline aggregates, and SBR serves to augment van der Waals interactions at the asphalt-aggregate interface, thereby amplifying interfacial bonding strength. However, when the content of SBR reaches 30%, some SBR molecules will be aggregated in the asphalt, which will lead to phase separation and affect the stability of the colloid. Therefore, it is recommended that the content of SBR should be limited to about 20% in practical engineering applications. In this work, the modification mechanism of SBR was analyzed at the molecular scale and verified experimentally, and the results provide a theoretical basis for the rational use of recycled SBR powder in asphalt applications.
摘要：
The accuracy of the data is crucial to the real-time prediction of autonomous driving. Due to factors such as weather and the accuracy of data collection equipment, there frequently exist noises in the data collected in real time. Therefore, it is necessary to perform analysis on acquired kinematic features related to driving behavior prediction. This study proposes a novel deep learning framework to explore influences of data noises on lane-changing intention prediction. Kinematic features including the longitudinal distance difference, velocity and acceleration, lateral velocity and acceleration of the vehicles are first extracted from the HighD. Then, the anti-interference performance of deep learning models such as transformer is tested. By comparing dataset with and without noises, we develop an evaluation method containing several predictive performance metrics and statistical measures. The results show that: (1) the longitudinal acceleration of the vehicle has the lowest sensitivity to noise, and the lateral velocity has the weakest anti-interference and the highest sensitivity. (2) The Bi-LSTM model with multi-head attention mechanism performs well in reducing the sensitivity of longitudinal acceleration and prediction accuracy. This study provides valuable information for data acquisition and model selection of real-time driving intention prediction.
期刊：
World Electric Vehicle Journal,2024年15(1):3- ISSN：2032-6653
通讯作者：
Chenhui Liu
作者机构：
[Qinglu Ma] School of Traffic and Transportation, Chongqing Jiaotong University, Chongqing 400074, China;[Meiling Su; Xuerui Hou] College of Civil Engineering, Hunan University, Changsha 410082, China;Research Institute of Hunan University in Chongqing, Chongqing 401120, China;Key Laboratory of Highway Engineering of Ministry of Education, Changsha University of Science & Technology, Changsha 410114, China;Author to whom correspondence should be addressed.
通讯机构：
[Chenhui Liu] C;College of Civil Engineering, Hunan University, Changsha 410082, China<&wdkj&>Research Institute of Hunan University in Chongqing, Chongqing 401120, China<&wdkj&>Key Laboratory of Highway Engineering of Ministry of Education, Changsha University of Science & Technology, Changsha 410114, China<&wdkj&>Author to whom correspondence should be addressed.
关键词：
traffic safety;electric vehicles;traffic accidents;accident size;ordered logit model
摘要：
With the great increase of electric vehicles (EVs) in the past decade, EV-involved traffic accidents have also been increasing quickly in many countries, bringing many new traffic safety challenges. Norway has the largest EV penetration rate in the world. Using the EV accident data from Norway in 2020 and 2021, this study aims to investigate the features of EV safety comprehensively. Firstly, a descriptive analysis is conducted. It has been found that rear-end collisions are the major collision type of EVs, and EVs are very likely to collide with pedestrians/cyclists. In addition, in terms of roadway type, EV accidents mainly occur on medium- and low-speed roads; in terms of environment, they mainly occur in good visibility conditions and dry road surface conditions. Then, a regression analysis is conducted to identify the key factors affecting the accident size, which is the number of traffic units involved in an accident and taken as the accident severity surrogate here. Since EV accidents are divided into four categories in order of accident size, the ordered logit model is adopted. It divides a multi-categorical dependent variable into multiple binary data points in order and calculates the probability of the dependent variable falling into each category with the logit model, respectively. The estimation results indicate that time of day, speed limit, and presence of medians have statistically significant impacts on the EV accident size. Finally, some countermeasures to prevent EV accidents are proposed based on the research results.
摘要：
Currently, the research on the mechanical properties of rubber-modified asphalt mixtures primarily focuses on small-scale investigations, with insufficient exploration into the performance of rubber particles and their relationship with the mechanism and properties of modified asphalt mixtures. Limited studies have been conducted on large-scale rubber modification in asphalt mixtures. Due to frequent use and subsequent high damage to existing asphalt pavements, incorporating rubber-modified asphalt mixtures can partially alleviate premature deterioration. Dynamic modulus tests were conducted using MTS equipment under unconfined conditions to investigate the viscoelastic behavior of rubber-modified asphalt mixtures with high rubber content and elucidate the influence of rubber particle content on the elastic deformation and recovery capability. The dynamic mechanical properties of the mixtures were determined at different loading rates, temperatures, and types of rubber-modified asphalt mixtures. Based on the test data, variations in the dynamic modulus, phase angle, storage modulus, loss modulus, loss factor, and rut factor of the rubber-modified asphalt mixtures under different loading frequencies, temperatures, and types were analyzed. The results demonstrate the pronounced viscoelastic behavior of rubber-modified asphalt mixtures. The mixtures exhibit enhanced elasticity at low temperatures and high frequencies, while their viscosity becomes more prominent at high temperatures and low frequencies. Under constant test temperatures, an increase in load loading frequency leads to a higher dynamic modulus; conversely, a decrease in dynamic modulus is observed with increasing test temperatures. The dynamic modulus of ARHM-25 at a frequency of 10 Hz is found to be 12.99 times higher at 15 degrees C compared to that at 60 degrees C, while at 30 degrees C, the dynamic modulus at 25 Hz is observed to be 2.72 times greater than that at 0.1 Hz. Furthermore, the rutting resistance factors of the asphalt mixtures increase with loading frequency but decrease with temperature. The rutting factor for ARHM-13 at a frequency of 10 Hz is found to be 22.98 times higher at 15 degrees C compared to that at 60 degrees C, while at a temperature of 30 degrees C, the rutting factor for this material is observed to be 3.09 times greater at a frequency of 25 Hz than at 0.1 Hz. These findings suggest that rutting is most likely when vehicles drive at low speeds in hot weather conditions.
摘要：
This study addressed the complex problems of selecting a constitutive model to objectively characterize asphalt mixtures and accurately determine their viscoelastic properties, which are influenced by numerous variables. Inaccuracies in model or parameter determination can result in significant discrepancies between the calculated and measured results of the pavement’s structural dynamic response. To address this, the research utilized the physical engineering principles of asphalt pavement structure to perform dynamic modulus tests on three types of high-content rubberized asphalt mixtures (HCRAM) within the surface layer. The research aimed to investigate the influencing factors of the dynamic modulus and establish a comprehensive master curve. This study also critically evaluated the capabilities of three viscoelastic models—the three-parameter solid model, the classical Maxwell model, and the classical Kelvin model—in depicting the dynamic modulus of HCRAM. The findings indicated a negative correlation between the dynamic modulus of the asphalt mixture and temperature, while a positive association exists between the loading frequency and temperature, with the impact of the loading frequency diminishing as the temperature increases. Notably, the three-parameter solid model was identified as the most accurate in describing the viscoelastic properties of the HCRAM. Furthermore, the dynamic response calculations revealed that most indexes in the surface layer’s dynamic response are highest when evaluated using the three-parameter viscoelastic model, underscoring its potential to enhance the pavement performance’s predictive accuracy. This research provides valuable insights into optimizing the material performance and guiding the pavement design and maintenance strategies.
摘要：
The asphalt mixture splitting test is one of the most important methods for measuring asphalt's tensile properties. To characterize the limitations of the traditional splitting test and the influence of the specimen size and loading conditions on the accuracy of the test, the factors affecting the strength of the splitting test were analyzed to reveal the splitting failure state and establish a unified representation model between the splitting and direct tensile tests. Initially, the moment of specimen cracking was taken as a key indicator, combined with image processing technology, to establish a set of criteria to judge the splitting test. Subsequently, standardized splitting tests were conducted and compared to tests of different specimen sizes and loading methods. Based on the octahedral strength theory, the stress points before and after the improved test were compared to the existing failure criteria. Direct tensile and splitting tests were conducted at different rates, and a unified strength-rate function model was established, realizing the unified representation of direct tensile and splitting tests. The research results indicate that the standardized splitting test is prone to the phenomenon wherein the specimen end face cracks before the center, affecting the accuracy of the test and potentially leading to redundant material strength evaluations. Using a loading method with a "35 mm specimen thickness" and a "0.3 mm rubber gasket + 12.7 mm arc-shaped batten" can essentially achieve the test hypothesis of "cracking at the center first", resulting in less discrete outcomes and closer alignment to the three-dimensional stress failure state. The tensile and splitting strengths are both power function relationships with the rate as the independent variable, establishing a unified function model of the tensile and failure strengths. The research provides a more reliable testing method and calculation model for asphalt pavement structure design, and it also provides an effective basis for the improvement of splitting tests on materials such as concrete and rock.
摘要：
The emission of volatile organic compounds (VOCs) from asphalt during construction processes presents substantial risks to human health and the environment. To advance sustainable transportation development, this review offers a comprehensive study of the methods for characterization, release characteristics, influencing factors, release mechanisms, and environmental impacts of asphalt VOCs. At present, research has been conducted on characterization methods, component characteristics, influencing factors, and environmental and health risks. The findings indicate that gas chromatography-mass spectrometry is the most comprehensive method for characterizing asphalt VOCs. Asphalt VOCs mainly comprise alkanes, aromatics, and aliphatic hydrocarbons. Factors including the temperature, asphalt source, and ultraviolet radiation can all affect the release characteristics of asphalt VOCs. Elevated VOC levels contribute to the photochemical production of ozone and fine particulate matter, exacerbating air pollution and climate change. Additionally, specific asphalt VOCs, including benzene and polycyclic aromatic hydrocarbons, pose health risks to humans. While progress has been achieved in the current research, challenges persist in quantifying VOCs, assessing their environmental impacts and health risks, and implementing effective mitigation technologies. To address these challenges, future research should focus on establishing asphalt VOC fingerprints, quantitative methods, evaluation criteria, material innovation, optimization of construction processes, exposure assessment, and collaborative solution implementation.
作者：
Chao Chen;Qinhao Deng;Chuangmin Li;Shuaibing Yi;Lubiao Liu
期刊：
Case Studies in Construction Materials,2024年20:e03038 ISSN：2214-5095
通讯作者：
Qinhao Deng<&wdkj&>Chuangmin Li
作者机构：
College of Civil Engineering, Hunan University, Changsha, Hunan 410082, China;School of Traffic and Transportation Engineering, Changsha University of Science and Technology, Changsha, Hunan 410114, China;Key Laboratory of Road Structure and Material of Ministry of Transport (Changsha), Changsha University of Science and Technology, Changsha, Hunan 410114, China;[Chao Chen] College of Civil Engineering, Hunan University,Changsha,Hunan 410082,China;[Qinhao Deng; Chuangmin Li; Shuaibing Yi; Lubiao Liu] School of Traffic and Transportation Engineering, Changsha University of Science and Technology,Changsha,Hunan 410114,China<&wdkj&>Key Laboratory of Road Structure and Material of Ministry of Transport (Changsha), Changsha University of Science and Technology,Changsha,Hunan 410114,China
通讯机构：
[Qinhao Deng; Chuangmin Li] S;School of Traffic and Transportation Engineering, Changsha University of Science and Technology, Changsha, Hunan 410114, China<&wdkj&>Key Laboratory of Road Structure and Material of Ministry of Transport (Changsha), Changsha University of Science and Technology, Changsha, Hunan 410114, China
摘要：
This study explores the potential applications of steel slag and tire pyrolysis oil (TPO) in creating self-healing road construction materials, aiming to address environmental concerns related to industrial waste and to extend the service life of roadways. A novel functional steel slag asphalt mixture was developed, utilizing steel slag as the aggregate and TPO as a healing agent. This agent permeates the pores of the steel slag, with microwave induction facilitating its controlled release. The research embarked on identifying the optimal process for preparing the functional steel slag aggregate through orthogonal experiments. It puts forward the optimum parameters of microwave induction based on the results of the low-temperature bending beam test and evaluates the effectiveness of the microwave-induced asphalt mixture’s self-healing. The study revealed that the recommended process for preparing functional steel slag aggregates is vacuuming the steel slag submerged in TPO for 30 minutes, followed by a soaking period of 10 minutes under standard atmospheric pressure, and concluding with a 48-hour standing period after removal from the TPO. Under this process, the absorption rate of TPO by steel slag reaches its maximum. Employing the Marshall test design method, the optimal asphalt-aggregate ratio was determined to be 5.15%. Significantly, the microwave heating rate of the functional steel slag asphalt mixture was found to be 3.25 times that of a conventional limestone asphalt mixture. The recommended microwave induction parameters were established at 700 W of power for a duration of 80 seconds. Initially, the crack healing rate reached 64.6%, which decreased to 47.6% after five microwave cycles. Remarkably, the healing rate of the functional steel slag asphalt mixture outperformed that of the ordinary steel slag asphalt mixture without TPO by 69.5% after the same number of cycles. These findings offer valuable contributions to the development of self-healing road construction materials, presenting a promising path for enhancing the durability of road infrastructures while addressing environmental challenges posed by industrial waste.
摘要：
This paper aims to incorporate the fractional derivative viscoelastic model into a finite element analysis. Firstly, based on the constitutive equation of the fractional derivative three-parameter solid model (FTS), the constitutive equation is discretized by using the Grunwald-Letnikov definition of the fractional derivative, and the stress increment and strain increment relationship and Jacobian matrix are obtained by using the difference method. Subsequently, we degrade the model to establish stress increment and strain increment relationships and Jacobian matrices for the fractional derivative Kelvin model (FK) and fractional derivative Maxwell model (FM). Finally, we further degrade the fractional derivative viscoelastic model to derive stress increment and strain increment relationships and Jacobian matrices for a three-component solid model and Kelvin and Maxwell models. Based on these developments, a UMAT subroutine is implemented in ABAQUS 6.14 finite element software. Three different loading modes, including static load, dynamic load, and mobile load, are analyzed and calculated. The calculations primarily involve a convergence analysis, verification of numerical solutions, and comparative analysis of responses among different viscoelastic models.
通讯机构：
[Li, X ] C;Changsha Univ Sci & Technol, Natl Engn Res Ctr Highway Maintenance Technol, 960,Wanjiali RD S,Sect 2, Changsha 410114, Hunan, Peoples R China.;Changsha Univ Sci & Technol, Sch Traff & Transportat Engn, Changsha 410114, Hunan, Peoples R China.;Ecole Ponts ParisTech, Lab Navier, CERMES, 6&8 Ave Blaise Pascal, F-77455 Marne La Vallee 2, France.
关键词：
Drop distance;Dynamic compaction;Ground improvement;Soil densification efficiency;Tamper weight
摘要：
Estimating the densification efficiency of soil fillers is the main topic in dynamic compaction (DC). However, existing methods fail to assess the different contributions between tamper weight (M) and drop distance (H). In this study, a DC laboratory setup was developed to allow such different contributions to be analyzed. A series of DC tests were conducted on a red clay from China with six combinations of tamper weight and drop distance and twenty multiple blows in each combination. The soil responses including crater depth, plastic deformation, impact stress, and inside stress spectrum were recorded. It was observed that with the same tamping energy and momentum, a heavier tamper with a lower drop distance enabled a deeper crater depth and larger plastic deformation. Further examination showed that a heavier tamper caused impact stress with a longer period, increasing the stress wavelength and propagation ability. Therefore, a larger soil body was involved in the compaction process. Additionally, with the same value of MH0.3, different combinations of tamper weight and drop distance shared similar impact stress and soil responses, which is recommended as the new index to estimate the DC densification efficiency for the studied red clay.
期刊：
Construction and Building Materials,2024年421:135710 ISSN：0950-0618
通讯作者：
Weiwei Han<&wdkj&>Hui Peng
作者机构：
National-Local Joint Laboratory of Engineering Technology for Long-term Performance enhancement of Bridges in Southern District(Changsha University of Science & Technology), Changsha, Hunan 410114, China;School of Civil Engineering, Changsha University of Science and Technology, Changsha, Hunan 410114, China;School of Traffic and Transportation Engineering, Changsha University of Science and Technology, Changsha, Hunan 410114, China;[Yigang Lv] National-Local Joint Laboratory of Engineering Technology for Long-term Performance enhancement of Bridges in Southern District(Changsha University of Science & Technology),Changsha, Hunan 410114,China<&wdkj&>School of Civil Engineering, Changsha University of Science and Technology,Changsha, Hunan 410114,China;[Jinghang Zhang; Miao Su; Xianliang He; Hui Peng] School of Civil Engineering, Changsha University of Science and Technology,Changsha, Hunan 410114,China
通讯机构：
[Weiwei Han; Hui Peng] S;School of Civil Engineering, Changsha University of Science and Technology, Changsha, Hunan 410114, China<&wdkj&>School of Traffic and Transportation Engineering, Changsha University of Science and Technology, Changsha, Hunan 410114, China
摘要：
To clarify the bond performance between steel rebar and ultrahigh performance concrete containing coarse aggregates (UHPC-CA), a total of 33 pull out specimens was cast. The effects of coarse aggregate particle size, coarse aggregate content, and steel fiber content on the failure modes and bond stress-slip curves of the specimens were studied. Based on the virtual crack model, considering the tensile contribution of steel fibers and the bridging effect of coarse aggregates, a model for the bond strength between UHPC-CA and steel rebar was established. The research findings indicated that there was a corresponding matching relationship between coarse aggregate particle size and the spacing of steel rebar ribs. In the 5–8 mm particle size group, the specimens showed 7.95% and 9.01% increases in bond strength compared to the 3–5 mm and 8–10 mm particle size groups, respectively. When the coarse aggregate content of UHPC-CA was 20%, the bond strength was the highest, increasing by 11.39% compared to specimens without coarse aggregates. The bond strength first increased and then decreased with increasing steel fiber content. Excessive steel fiber content could lead to the clustering of steel fibers, reducing the effective number of steel fibers contributing to toughening. The calculated results from the established bond strength model were compared with experimental and literature results, yielding an average ratio of 0.993 and a standard deviation of 0.166. This model effectively predicts the bond strength between UHPC-CA and steel rebar.
摘要：
Based on the orthogonal test method, the mixture proportion design of cement-stabilized macadam (CSM) modified with rubber powder and fiber is studied. With strength and shrinkage as key indices, the influence of length of polyvinyl alcohol (PVA) fiber, fiber content, particle size of rubber powder, and rubber powder content on the performance of CSM analyzed, and the optimum mixing proportion is determined. Based on this, the modification mechanism of CSM by rubber powder and fiber is further studied from a micro perspective. results show that the 7-day unconfined compressive strength of CSM gradually increases the increase of fiber length. With the increase of fiber content, the compressive strength shows a trend of first increasing and then decreasing. The 7-day unconfined compressive strength CSM gradually increases with the increase of rubber powder mesh size and linearly decreases with the increase of rubber powder content. The 28-day average dry-shrinkage coefficient CSM shows a trend of first decreasing and then increasing with the increase of fiber length fiber content, and gradually increasing with the increase of rubber powder mesh number rubber powder content. Considering the strength and shrinkage characteristics, the optimum mixing parameters are 40 mesh rubber powder, 0.5 % rubber powder, 18-mm fiber length, and 1.2-kg/m3 fiber content. Scanning electron microscopy results show that there is a between the rubber powder and the cement matrix, and the interface between the two is continuous, with weak bonding, resulting in a decrease in the compressive strength of PVA fiber can improve the toughness of CSM. It has good adhesion with cement matrix. It forms a three-dimensional network support structure in the CSM mixture and can restrain water loss in the cement matrix, thus greatly improving the cracking resistance of CSM.
摘要：
Cold-mixed epoxy asphalt (CEA) is a superior pavement material that can be constructed and cured at room temperature, attracting increasing attention. However, the lack of research on CEA molecular model selection, structure, and energy evolution during curing has limited the accuracy of CEA performance research. To address this, three kinds of CEA molecular models were established: the Mixing model, the epoxy resin (ER)-asphalt interface (RA) model, and the ER-asphalt-ER interface (RAR) model. Their accuracy in describing the basic properties, structure, energy evolution, and mechanical properties of CEA was investigated and compared with experimental results. The RAR model was found to be the closest to the real structure. The curing process did not change the phase structure of CEA significantly, which maintained a "sea-island" structure with new hydrogen bonds forming between the ER and asphalt molecules. The crosslinking of ER consumed polar epoxy groups in CEA, resulting in a decrease of valence bond energy by up to 29.1% and an increase of van der Waals energy by up to 104.3% for the RAR model. The curing network also restricted the molecular chain movement and fixed the intermolecular distance and orientation. It was suggested that uniaxial tension simulation should be performed at 3 x 10-5/fs under the NPT ensemble when not studying yield behavior. The main fracture mechanisms of CEA were crack deflection, pinning, debonding, and asphalt particle pull-out. Many short-range rigid segments in CEA also explained its high strength.
