A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Prediction of Permanent Deformation in Asphalt Concrete(2012) Carvalho, Regis Luis; Schwartz, Charles W; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Permanent deformation is a major distress in flexible pavements that leads to the development of rutting along the wheel path of heavily trafficked roads. Early detection of rutting is very important for preventive maintenance programs and design of rehabilitation strategies. Rutting by definition is the accumulated permanent deformation that remains after removal of the load. Rigorous modeling of permanent deformations using nonlinear finite element analysis based on the correct physical mechanism of residual deformations after removal of the load provides important insights into the rutting problem. This dissertation documents the study of permanent deformation in asphalt concrete in pavement structures using a fully mechanistic model based on Schapery's viscoelasticity and Perzyna's viscoplasticity theories. The model is calibrated and implemented in a 3D finite element commercial software package. Two calibration procedures are performed and discussed. Two immediate practical applications are shown and a simulation of full scale accelerated pavement test is performed. This research demonstrates that the Perzyna-HiSS viscoplastic model can be successfully calibrated using either research-grade creep and recovery tests or the more simple and production-oriented Flow Number test. The importance of induced shear stress reversals under a moving wheel load is documented. The 3D finite element simulation is then used to identify the fundamental differences on how rutting develops in different pavement structures in terms of the differences in the transverse profile and distribution of rutting within the layer. The analysis results are used to develop new pavement-specific depth functions for potential future incorporation into the AASHTO Mechanistic-Empirical Pavement Design Guide (MEPDG). Lastly, the 3D finite element model is used to predict rutting at one lane of the FHWA's full-scale Accelerated Load Facility experiment. After correction for some anomalies during the early loading cycles in the experiment, the predicted and measured rutting at the center of the wheel path were in good agreement.Item MECHANISTIC-EMPIRICAL DESIGN OF FLEXIBLE PAVEMENTS: A SENSITIVITY STUDY(2006-03-14) Carvalho, Regis Luis; Schwartz, Charles W; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Pavement structural design is a daunting task. Traffic loading is a heterogeneous mix of vehicles, axle types and loads with distributions that vary daily and over the pavement design life. Pavement materials respond to these loads in complex ways influenced by stress state and magnitude, temperature, moisture, loading rate, and other factors. Environment exposure adds further complications. It should be no wonder the profession has resorted to largely empirical methods. Developments over recent decades offered an opportunity for more rational and rigorous pavement design procedures. The latest of these accomplishments is the development of the mechanistic-empirical pavement design procedure in NCHRP Project 1-37A. This study presents a comparison of flexible pavement designs between the 1993 AASHTO guide and the NCHRP 1-37A methodology and a sensitivity analysis of the NCHRP 1-37A's input parameters. Recommendations for future studies involving the application and implementation of the new mechanistic-empirical pavement design guide concludes the study.