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Executive Summary

This report highlights findings from the FHWA DTFH61-05-H-00019 project, which focused on the development of the multiaxial viscoelastoplastic continuum damage (MVEPCD) model for asphalt concrete in both compression and tension. The MVEPCD model and finite element package (FEP++) have been developed for this purpose. The MVEPCD model combines elements of viscoelasticity, continuum damage mechanics, and viscoplasticity to model the material behavior. FEP++ is used to model the interaction of material and structure.

An introduction that outlines the research objectives and scope of the project is given in chapter 1 of this report. Chapter 2 provides a practical review of the underlying theories for the MVEPCD material model. Particular attention is paid to the concept of continuum damage mechanics and their implementation with viscoelastic materials. In addition, methodologies used to characterize the MVEPCD model are outlined in chapter 2. Details regarding specimen fabrication and testing protocols as well as background for the materials tested are in chapter 3.

Experimental results are categorized by loading direction, tension, or compression in chapter 4 and chapter 5, respectively. Specific comparisons of the effects of direction of loading are given in subsections 5.2.2 and 5.2.4. Each chapter provides the procedure for characterizing the viscoelastoplastic continuum damage (VEPCD), beginning with the linear viscoelastic characterization, proceeding to the viscoelastic damage characterization and viscoplastic characterization, and ending with the validation of the models. In addition, there is some discussion about the engineering properties of the materials in compression and tension, as well as verification of the time-temperature superposition (t-TS) principle with growing damage. Chapter 4 discusses the use of the VEPCD model for fatigue predictions. Because the rutting distress, a permanent deformation phenomenon, is related primarily to the compressive behavior of asphalt concrete, chapter 5 focuses on the viscoplastic behavior of the material in compression.

Chapter 6 presents the research efforts to enhance the finite element program with the viscoelastic continuum damage (VECD) model and the viscoelastic continuum damage model included in finite element package (VECD-FEP++). The resulting program is then used in chapter 7 to perform the three-dimensional (3D) finite element analysis to study the effects of temperature, material type, and vehicle speed on pavement responses. Chapter 8 summarizes the conclusions from both the experimental and computational work for this project. The future direction of the research at hand is provided at the end of chapter 8 as well.

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