Graduate Thesis Or Dissertation
 

Development of a Reliability-Based Framework and Empirical Models for Justifying Allowable Chloride Limits and Quantifying Critical Input Variables for Predicting the Service Life of Reinforced Concrete Structures

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/wm117v19g

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  • Significant progress has been made over the past 20 years in developing models to estimate the service-life of reinforced concrete systems. The basic understandings of the mechanisms that control the transport of ions and moisture in concrete systems have been well researched and models for determining corrosion initiation, specifically chloride-induced corrosion initiation of the steel reinforcement, are commonly used in the engineering community. Although several models are available, with each possessing benefits and challenges, the more commonly used model to estimate service life is based on Fick’s Second Law. The classical solution to this partial differential equation for predicting the service life of reinforced concrete structures requires information on the following variables be known: the apparent diffusion coefficient (Da), the critical chloride threshold (CT), the initial “background” chloride concentration (Ci), the surface chloride concentration (Cs), and the depth of concrete cover (x). Because there is a lack of standardized testing, the literature possesses a wide range of values and distributions for these input variables (with the exception of cover depth). To prevent the risk of corrosion of reinforcing steel in the concrete structures exposed to chlorides, many organizations such as American Concrete Institute (ACI) and State Highway Agencies (SHAs) limit the amount of admixed chlorides that can be included in new concrete. This limit is referred to as the allowable chloride limit, CA. However, the SHAs and concrete organizations publish a wide range of CA limits, seemingly without any scientific justification, which leads to further uncertainty. This variability creates confusion among the users of such documents and the potential for the construction of short-lived reinforced concrete structures or overly conservative and costly requirements. To reduce the uncertainty in the outputs of service life models and quantifying the critical parameters that affect the service life prediction, this dissertation investigates the following topics: (1) Development of a risk-based framework to standardize the process of selecting CA limits using First Order Reliability Method (FORM) and spatial statistics. The proposed model estimates the probability of corrosion initiation given a selected CA limit through the expected life of the structure. (2) Development of a hierarchical Bayesian model for CT based on the reported CT values in the literature. The developed model accounts for the influence of cement type, supplementary cementitious materials, water-to-binder ratio, and the surface condition of the reinforcing steel on CT. (3) Development of a new time-variant model of Cs, which incorporates the effects of time to exposure and the effects of the concentration of chlorides in the exposure environment. The model assumes that Cs is sigmoidal in shape with an asymptote that is a function of the concentration of chlorides in the environment. The input variables for the proposed model were selected based on the results of the experimental work to determine the influence of water-to-cement ratio, time to exposure, the concentration of chlorides in the exposure environment, and exposure time on Cs. (4) Three new models are proposed to determine the admixed chloride binding capacity of several cementitious systems containing OPC, fly ash Type C and F, slag, and silica fume with different replacement levels. Furthermore, the influence of water-to-binder ratio and admixed chloride levels on binding capacity of cementitious system is explored.
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  • Existing Confidentiality Agreement
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  • 2018-01-23 to 2019-11-28

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file details ShakouriHassanabadiMahmoud2017.pdf 2018-01-23 Público Baixar