Abstract:
High performance cementitious composites (HP2C) are a new generation of fiber reinforced cementitious composites (FRCC) with substantial improvements in mechanical behavior. The most important development in these HP2C materials may be the nearly elasto-plastic ductile behavior, which allows safe exploitation of the tensile and shear capacity in structural elements. This thesis presents a comprehensive investigation into the ductility enhancement of HP2C structures. Beginning at the micromechanical level, sources of ductility are examined and micro-to-macro relations are derived from homogenization theory and fracture mechanics. These micro-to-macro relations form the basis for a novel 3-D two-phase material model, which captures macroscopically observed behavior. Currently existing models which describe the mechanical behavior of FRCC are often micromechanical in nature. However, this macroscopic approach permits one to model the mechanical behavior of HP2C in a continuous fashion, i.e. through the various states of cracking in HP2C, while capturing - through the two-phase composite structure of the model - the micromechanical sources of energy dissipation in the fiber reinforced composite.(cont.) The 3-D model is implemented in a finite element program to simulate the behavior of two HP2C applications: a flexural girder and a shear girder, which have recently been tested by the FHWA. It is shown how the two-phase model aptly and accurately predicts the structural behavior of HP2C. Next, a sensitivity analysis of the HP2C model parameters elucidates how changes in HP2C mechanical behavior, observed at material level, manifest themselves at the structural level. By setting limits on the permanent composite matrix strain, which accounts for cracking in HP2C, one can set service limits on HP2C structures.Hence, a comprehensive (micromechanical, macroscopic, and structural) method for the assessment of the ductility enhancement of HP2C structures is presented. A significant scientific benefit of this research is the HP2C model which links micromechanical processes to macroscopic behavior and ultimately to structural behavior. This research also provides a design tool, that is the finite element application, which can be used to predict the behavior of HP2C structures and suggest improvements in HP2C structural and material design.
Description:
Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2002.Includes bibliographical references (p. 280-287).
