Due to its large-scale open porosity, pervious concrete offers several performance attributes that can be applied within the civil infrastructure. One notable attribute of pervious concrete is its high hydraulic conductivity, which can be used for in situ drainage of rainwater from paved surfaces, providing significant environmental benefits. However, the large-scale porosity negatively impacts strength and some other measures of mechanical performance, which may become problematic in structural applications. Furthermore, the connected nature of the porosity may accentuate interactions with the ambient environment. In particular, there is a potential for rapid drying of the bulk material that does not exist for ordinary concretes.
Based on these observations, this dissertation attempts to elucidate fundamental behaviors of pervious concrete through experimental and numerical modeling exercises defined at the material meso-scale, at which the material phases (aggregate, cement paste matrix, aggregate-matrix interface, and large-scale pores) are explicitly represented. Integration of the experimental and numerical modeling components is accomplished by establishing, to the extent practical, one-to-one correspondence between the physical and numerical models. On the modeling side, this involves several simplifying assumptions including the use of mono-sized spherical (or disc-shaped) aggregates and uniform thickness of the paste layers encompassing the aggregates. On the experimental side, spherical glass aggregates are used in several series of test specimens, but without any control over the spatial distribution of the cement paste matrix. The numerical simulations of this model pervious concrete are based on lattice representations of the relevant mechanical and environmental field variables. In particular, rigid-body-spring networks represent the mechanical behavior of the model pervious concrete; the moisture field is represented by a corresponding lattice of conduit elements. Both networks share the same nodal point locations, which facilitates the coupling of mechanical and hygral actions. Despite the simplifications introduced by the model pervious concrete, domain discretization is a challenging task. Approaches for discretizing pervious concrete, amenable to the lattice model requirements, are introduced. The numerical modeling exercises are valuable, as they provide a quantitative view of behavioral mechanisms at the material meso-scale.
The physical and numerical modeling components of the research tend to confirm expected behaviors. For example, mixture design (in terms of amounts of cement paste matrix, aggregates, and pore space) has a primary influence on properties of interest, including strength and drying shrinkage. Due to the nature of pervious concrete and its methods of production, the material structure and properties are highly variable, relative to conventional concrete materials. Stress analyses show the presence of discrete load paths and stress concentrations within the pervious concrete, not only under applied loading but also for the case of drying shrinkage. Stress concentrations tend to form in the paste zones that bridge neighboring aggregates, which raises concerns regarding resistance to fatigue loading. The stiff, dimensionally stable aggregates restrain drying shrinkage of the paste and thus the macroscopic shrinkage of the pervious concrete volume. The shrinkage of pervious concrete prisms is much less than that of the control paste specimens, in accordance with experimental measurements. The large-scale open porosity increases the rate of drying of the bulk volume of pervious concrete, relative to that of the control specimens. The tensile stresses in the paste layers surrounding the aggregates are large enough to induce microcracking, even without external restraints on the pervious concrete volume. Such microcracking, not considered in these analyses, would likely reduce drying shrinkage over time. The modeling framework developed in this study can be extended to provide more accurate representations of pervious concrete, including its behavior under varying environmental conditions.
|Advisor:||Bolander, John E.|
|Commitee:||Harvey, John T., Miller, Sabbie A.|
|School:||University of California, Davis|
|Department:||Civil and Environmental Engineering|
|School Location:||United States -- California|
|Source:||DAI-B 81/12(E), Dissertation Abstracts International|
|Subjects:||Civil engineering, Computer Engineering, Materials science|
|Keywords:||Drying shrinkage, Fracture, Lattice model, Pervious concrete, Porosity, Stress concentration|
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