Experimental Investigation and Multi-Physics Computational Modeling for Assessment, Mitigation and Prevention of Concrete Deterioration

Faysal Bousikhane

doi:https://doi.org/10.21985/n2-9g2j-k858

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Experimental Investigation and Multi-Physics Computational Modeling for Assessment, Mitigation and Prevention of Concrete Deterioration

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Precise assessment of long-term aging and deterioration play a major role in life-time predictions of concrete structures. One of the primary challenges in studies of cementitious materials such as concrete comes from the fact that multiple chemical reactions are happening in parallel. Environmental conditions present another challenge as they can influence greatly chemical kinetics, further complicating the analysis. The deterioration mechanism studied in this thesis is a chemical reaction called Alkali Silica Reaction (ASR) wherein an expansive gel is formed causing significant concrete degradation over time.', '\tASR induced degradation of concrete is first investigated through experimental methods to assess ASR affected concrete mechanical properties evolution over one year. The influence of environmental properties, aggregates silica content, aging, shrinkage, creep and sample geometry on ASR are fully characterized through a comprehensive experimental program involving destructive and non-destructive evaluations of reactive and non-reactive concrete samples at different stages. \\newline', '\tWhile experimental investigations happen to be the first step in the study of physical phenomenons, practical limitations in physical testing have constantly led researchers to develop numerical models capable of modeling accurately concrete properties. Besides, the long term assessment of concrete properties evolution is only achievable through the development of powerful models that can couple realistically the aforementioned physical phenomenon. The Lattice Discrete Particle Model (LDPM), a three-dimensional mesoscale discrete model, is employed in this study to simulate the mechanical response of concrete at the level of coarse aggregate pieces. The LDPM is capable of characterizing strain localization, distributed cracking in tension and compression, and to reproduce accurately post peak softening behavior. The M-LDPM, an extension of LDPM, includes multiple models that describe heat transfer, moisture transport as well as ASR, creep, aging, shrinkage, fiber contribution to concrete strengthening and their full coupling. The M-LDPM is calibrated and validated by modeling the experimental results obtained during the initial phase of the ASR study.', '\tHigh costs associated with concrete structure rehabilitation has pushed researchers to develop a new promising generation of self-healing concretes. As their name suggests, self-healing concretes are capable of mitigating damages associated with a given deterioration mechanism (ASR for example) by automatically regenerating themselves post-damage. This feature is crucial in the mitigation of deterioration mechanisms since fractures behave like hydraulic pathways, significantly increasing local permeability and promoting water ingress. The presented work includes an experimental study characterizing the effects cracks and of a self-healing admixture (Penetron) on concrete permeability. This study is completed by the development calibration and validation of a multi-physics computational framework which couples successfully mechanical and moisture transport behavior in concrete. ', '\tLast but not least, prophylactic methods have been developed to counter and limit deterioration mechanism consequences. One example is the use of Fiber Reinforced Ultra High Performance Concrete (FRUHPC) mixes as overlays on cracked bridge decks. In this thesis, simulations were performed to identify the impact of various steel fiber types on the mechanical response of an ultra-high performance concrete (UHPC) developed by the US army Corps of Engineers. This type of concrete has outstanding mechanical properties in compression as well as in tension in comparison to regular concrete. The simulations were performed with the LDPM-F, an extension of the LDPM capable of modeling fiber effects.

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