Shrinkage, residual stress, and cracking in heterogeneous materials
Abstract
Concrete experiences volumetric changes as a result of material formation (cement hydration), thermal variations, or moisture losses. If these volume changes are prevented by the structure surrounding the concrete or volumetrically stable phases inside the concrete, residual stresses can develop. In many cases, these residual stresses may be large enough to result in cracking. While the premature cracking of concrete is significant enough to be considered in the design of concrete facilities, existing test methods and design methodologies need to be updated to better quantify the cracking potential especially when the concrete experiences non-uniform deformations. Most design and testing approaches assume that concrete behaves like a homogeneous material. However, concrete is a composite that consists of cement paste and aggregates that have dissimilar material properties. When concrete changes its volume, localized internal residual stresses develop due to heterogeneity (i.e., paste and aggregates) that could lead to microcracking and premature cracking of concrete. Therefore, to properly evaluate the cracking behavior of concrete, an analytical tool considering the heterogeneous nature of concrete should be developed. This research begins with quantifying the impact of non-uniform shrinkage on the residual stress development in the restrained ring test considering that the concrete experiences non-uniform moisture loss (drying). The role of the boundary conditions and the degree of restraint on residual stress development is also discussed. Next, the internal residual stresses that develop in a multi-phase composite system are examined by varying the series of parameters (material properties of each-phase, volume fraction of aggregate, and bond conditions between the phases). Analytical modeling is used to assess the microcracking and cracking behavior of concrete composite systems using the object-oriented finite element code. It is the hypothesis of this research that the cracking behavior of concrete can be properly evaluated by assuming that concrete is a heterogeneous multi-phase composite with the assistance of a recently developed object-oriented finite element code that enables meshing a complex material meso-structure using optical mesostructural images. Although this research focuses on shrinkage in cementitious composites only, this software could have numerous applications in determining damage development in other composites as well.
Degree
Ph.D.
Advisors
Weiss, Purdue University.
Subject Area
Civil engineering
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