The short-term goals of this integrated research and education activities within the project period include: 1) development of a microstructure-based discrete element modeling approach to characterize asphalt materials; 2) implementation of the model to evaluate asphalt material response and performance to improve pavement structural design; 3) integration of the proposed research activities into the educational programs for high school students, K-12 educators, and undergraduate and graduate students, and; 4) dissemination of the research results through publications, conferences, and professional development for practicing professionals. The long-term goals are to: 1) establish a multi-user research and education center for asphalt material and virtual testing by integrating the proposed advanced modeling approach, and; 2) implement advanced technologies into pavement materials, locally through the Michigan Department of Transportation, and broadly through research collaborators and industry partners. This project will: 1) advance the understanding of asphalt pavement materials and pavement structures; 2) increase collaboration among researchers at many leading institutions and industries; 3) enhance scientific and technological understanding of micromechanical aspects of pavement infrastructure, and; 4) significantly reduce the cost of pavement infrastructure construction and maintenance. The development and application of the microstructure-based discrete element model in asphalt materials will enhance understanding by correlating material behavior to pavement performance. The research will translate directly into improved asphalt mixture design and pavement thickness design. This in turn should create substantial cost savings. A one-percent decrease in asphalt concrete life-cycle cost would amount to approximately $500 million in U.S. Federal government savings alone. Activities are planned to advance discovery and understanding of asphalt pavement infrastructure materials while promoting teaching, training, and learning through specific activities for K-12 students and teachers, undergraduate and graduate engineering and science majors, and practicing engineers.
NSF GRANT # 0701264 PI: Zhanping You Asphalt materials are usually on the top layer of an asphalt road. There is a common misconception that asphalt materials are cheap, low-tech and simple. However, driven by the current high costs for oil and transportation and the need to develop sustainable transportation infrastructure, this is no longer the case. The asphalt material is a composite material of mineral aggregates, asphalt, additives, and air voids. spatial distribution and the proportions of those components could significantly impact the performances. Evidently, it is almost impossible to fully understand such a complex material without utilizing advanced technologies. Therefore, asphalt materials are not low-tech and simple, but high-tech and complex if one pursues deeper insights into the fundamentals. In this project, the research team applied discrete element model (DEM) to simulate the mechanical response of asphalt materials from a microstructure perspective as seen in the Figure. The main achievements for the simulation work include: 1) Better understand the mechanical responses of asphalt materials from microstructure aspect. The asphalt materials include the asphalt binder and asphalt mixtures in the laboratory and the asphalt pavement in the field. For instance, the research team applied the DEM to know the deformation of road materials when a trucks are driving on the roads. This mechanical response is very important to discover the mechanism of the various diseases of roads. 2) The research team applied DEM to predict the performances of road materials and pavements. When the basic properties of asphalt and stones are known, the properties of the asphalt road materials or the road can be obtained through the prediction. Further, mechanical performances of asphalt mixtures or asphalt pavements can be predicted, such as the rut and cracks. 3) The project successfully achieved the three-dimensional (3D) discrete element (DE) models of asphalt mixtures under dynamic loads. In this effort, the 3D DE modeling of the visco-elasticity was conducted with the reconstruction of the asphalt mixture microstructure. The research team made significant contribution to the development of the discrete element technique, including: 1) Develop useful asphalt models such as randomly generated models and user defined models, which means less manpower and more economical compared to the traditional image-based models; 2) Expand the DEM models from two dimensions to three dimensions, which is more accurate for the real world situation and therefore more reliable; 3) Develop DEM models from elastic to viscoelastic world, which is more representative for asphalt materials. 4) Explored a better way to reduce the computational time for the simulation. It is known that the three dimensional DEM simulation for viscoelastic models is very time consuming work, however, the new method discovered in this project is very desired. The graduate students have learned how to model the contact force between aggregates in asphalt mixtures. They also learned how to use discrete element models with consideration of the viscoelastic properties of the heterogeneous media. Two PhD students prepared dissertations on this funded project. Other graduate and undergraduate students have learned how to use the advanced Superpave laboratory. They have an excellent opportunity to add laboratory experience to their in-class theoretical studies. They are trained in the Asphalt Binder Rheology Research and Testing Facility, and the Hot Mix Asphalt Research and Testing Facility. The undergraduate students have been closely worked with the PI and PhD students in the past a few years. Many graduate students were involved in this project and learned various skills. The research team also worked in outreach activities beyond of the research. The activities include teaching and assisting the Pavement Design, Construction, and Materials (PDCM) Enterprise. The research team hired many PDCM students in the research work as hourly undergraduate researchers. This research project also advanced the discovery and understanding of asphalt pavement infrastructure materials while promoting teaching, training and learning through specific activities for undergraduate and graduate engineering and science majors, and practicing engineers as the following specific activities: 1) The research team focused on the recruitment of a diverse group of traditionally underrepresented (female, urban, rural, minority and/or socio-economically disadvantaged) students to participate in the project activities. 2) The research team enhanced scientific and technological understanding of material behavior. This has been reflected in the published papers. 3) The research team has enhanced civil engineering courses at Michigan Technological University that incorporated the research results. 4) The research team is creating new research networks through collaborations with researchers and scientists from other institutions. This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
