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Tongjing, China

Qian Z.,Nanjing Southeast University | Wang J.,Suzhou Highway Bureau | Wang L.,Virginia Polytechnic Institute and State University
Geotechnical Special Publication | Year: 2014

To describe the crack development of epoxy asphalt concrete (EAC) from the three-dimensional (3-D) scale perspective, a 3-D heterogeneous digital sample independent of laboratory is reconstructed. A bilinear cohesive-softening model is implemented into the discrete element method (DEM) framework to simulate the crack behavior. The corresponding micromechanical models describing the interaction of micro-scale components of the virtual specimen are assigned. The simulation results of a single-edge notched beam test are shown to compare favorably with the experimental results and accurately capture the distributions of fracture zone and stress within the model. The developed 3-D visualization modeling technique is capable of simulating the initiation and propagation of cracks during the bending fracture of EAC. ALso the 3-D user-defined microstructural DEM fracture model also has the potential ability to help understand various fracture mechanisms and shows a realistic cracking process of quasi-brittle materials such as EAC. © ASCE 2014. Source


Qian Z.-D.,Nanjing Southeast University | Wang J.-Y.,Suzhou Highway Bureau
Gongcheng Lixue/Engineering Mechanics | Year: 2015

In order to determine the critical points of the crack initiation and unstable propagation for epoxy asphalt concrete (EAC), firstly, a three-dimensional (3D) virtual specimen of EAC with heterogeneous (coarse aggregates, asphalt mastic and air voids) and multilayer (aggregate gradation) morphological features was reconstructed. Secondly, the virtual three-point bending test of a single-edge notched beam was implemented using the discrete element method (DEM), and a digital camera method was used to capture the surface crack development of the experimental beam specimen. Finally, the changing relationship between the crack tip opening displacement (CTOD) and the crack mouth opening displacement (CMOD) throughout the crack development was analyzed. The results indicate that the introduction of δ25 representing CTOD provides a new idea for understanding the energy occurring in the fracture zone used for crack propagating. Additionally, the two governing points on the relationship curve between CTOD and CMOD approximately describe the initiation and critical unstable propagation of cracks, respectively. Meanwhile, the crack development of EAC includes three stages, namely, initiation, stable and unstable propagation. Furthermore, it is found that the analysis method based on the δ25-CMOD curve can be used as a supplemental tool to investigate the fracture behavior of EAC. ©, 2015, Tsinghua University. All right reserved. Source


Qian Z.-D.,Nanjing Southeast University | Wang J.-Y.,Suzhou Highway Bureau | Chen L.-L.,Nanjing Southeast University | Wang L.-B.,Virginia Polytechnic Institute and State University
Journal of Testing and Evaluation | Year: 2015

Cracking in epoxy asphalt concrete (EAC) used for a steel bridge wearing course has always been a major cause of structural and functional deterioration of this material, particularly in cold climate. Therefore, it is important to understand the complex fracture behavior of this heterogeneous mixture, which is composed of irregularly shaped and randomly distributed aggregates surrounded by asphalt mastics. A three-dimensional (3D) fracture model independent of laboratory, based on the discrete element method (DEM), is reconstructed using a randomly generating algorithm to investigate the fracture behavior. A bilinear cohesive-softening model is implemented into the DEM framework to simulate the crack initiation and propagation in EAC. Several experimental tests are performed to obtain input parameters of materials for numerical models. The simulation results of a single-edge notched beam test agree well with experimental results and accurately capture the stress distribution and development of fracture zone. The modeling technique herein provides insight into the progressive cracking process; 3D visualization of crack trajectories also demonstrates the influence of heterogeneity on crack path. The 3D user-defined microstructural DEM fracture model is capable of giving a realistic cracking process of quasibrittle materials such as EAC and can help us better understand various fracture mechanisms through numerical simulations. Copyright © 2014 ASTM International. Source


Chen L.,Nanjing Southeast University | Qian Z.,Nanjing Southeast University | Wang J.,Suzhou Highway Bureau
International Journal of Geomechanics | Year: 2016

Cracking is a major distress in steel bridge deck pavements. To determine the critical cracking zone, a numerical multiscale structural analysis was proposed and performed on the basis of a case study. First, a whole bridge model was analyzed, which revealed that the critical segment under critical load combination was one-fourth of the bridge span. Second, the critical segment was modeled using the finite mixed element method, and the critical local plate was determined. Third, using a submodel technique, the critical orthotropic steel plate with pavement was analyzed. The constructed model was then updated through an equivalent impact factor obtained from a numerical model analysis that considered vehicle-pavement interaction. From such multiscale model analysis, the crack distribution law of steel deck pavements was determined. Comparison of the analysis results from a traditional model with the multiscale model revealed the non-negligible effects of bridge structure and pavement evenness. Findings from this study may provide guidance for improving the preservation practice of steel deck pavements. © 2015 American Society of Civil Engineers. Source

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