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Title:Understanding and predicting transient material behaviors associated with mechanical resonance in cementitious composites
Author(s):Bittner, James Alan
Director of Research:Popovics, John S
Doctoral Committee Chair(s):Popovics, John S
Doctoral Committee Member(s):Weaver, Richard L; Roesler, Jeffery R; Ten Cate, James A
Department / Program:Civil & Environmental Eng
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Sequential Impact
Nonclassical Nonlinear
Slow Dynamics
Abstract:Cementitious composite materials provide a foundation for civilized life, from underlying structural bedrock to the tallest concrete structures in the world. These infrastructure materials (e.g., concrete and rock) are challenging to inspect and characterize, in part because of their heterogeneous and multi-scale compositions. Recently, nonlinear transient dynamic mechanical resonance behaviors, also known as “slow dynamic” behaviors, have been observed in damaged cementitious composite materials, yet the physical mechanisms underlying these behaviors are not understood. These phenomena hold potential to offer new insight and improved performance for monitoring the degradation of infrastructure materials. In this dissertation, I study the potential of slow dynamic behaviors for practical application as a nondestructive inspection method for infrastructure materials. The study includes experimental tests and analytical modeling. Most experiments were carried out on neat cement paste samples, which represent porous composite infrastructure materials in general. The study was divided into three components: observing the behavior at the global (macro) and micro-scales, modeling the behavior in terms of a physical or mechanistic basis, and applying the behavior to monitor degradation through a practical application. A repeatable nondestructive testing approach that uses a sequential impact device was designed to extract consistent global slow dynamic conditioning observations and characteristics from prismatic cement samples. The occurrence and existence of slow dynamic behaviors depended on the extent of damage and moisture states of a specimen. A small-scale disc vibration experiment was designed to enable imaging, using an environmental scanning electron microscope during vibration excitation in a controlled environment. Moisture migration within the paste microstructure was observed at the micron scale before and after resonance vibration of the disc. A new Mechanistic Diffusion Model (MDM) was developed to explain observed global- and micro-scale experimental results. The MDM unifies the moisture state, damage extent, and time dependence of slow dynamic behaviors. The MDM was verified through further experimentation. Finally, the slow dynamic characteristics of drying cement paste prisms with varying amounts of shrinkage reducing admixture were studied and compared to linear measurements performed on the same samples. The slow dynamic behaviors provided a measure of the bulk relative material damage at a single point in time, whereas the linear methods required measurements at two different points in time, before and after damage, in order to characterize the material. This dissertation provides a deeper understanding of slow dynamic behavior, offers a new mechanistic explanation based on moisture migration for slow dynamic behaviors in porous composite materials, and presents the basis for a single-test nondestructive approach to evaluate degradation levels in cementitious materials in a sensitive and reliable manner. The improved understanding of these dynamic behaviors will improve the design, application, and evaluation of infrastructure materials, from understanding underlying bedrock seismicity to improving structural assessments of concrete.
Issue Date:2018-11-29
Rights Information:Copyright 2018 James A. Bittner
Date Available in IDEALS:2019-02-08
Date Deposited:2018-12

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