Graduation Year

2022

Document Type

Thesis

Degree

M.S.M.S.E.

Degree Name

MS in Materials Science and Engineering (M.S.M.S.E)

Degree Granting Department

Engineering

Major Professor

Christopher Alexander, Ph.D.

Committee Member

Micheal Cai Wang, Ph.D.

Committee Member

Katherine Alfredo, Ph.D.

Keywords

Anodized Aluminum, Bipolar Electrochemistry, Corrosion, Impedance

Abstract

This is a two-part thesis with the overall investigation technique being electrochemical impedance spectroscopy (EIS). In the first part, EIS is used to estimate the layer thickness of anodized aluminum oxide. This required the development of an appropriate electrical circuit model; that with parameters that correspond to physical properties of the oxide. In this work, it was found that for thicker oxides of which the outer porous layer is greater than 12 microns, impedance may be used to estimate the outer layer thickness. However, further research is required to understand the role of outer porous layer structure on the impedance response towards improved accuracy.

In the second part of this thesis, a novel impedance technique called bipolar electrochemical impedance spectroscopy (BPEIS) is investigated. BPEIS was previously explored as a potential nondestructive method for detecting corrosion of steel in post-tensioned tendons which are used as reinforcing structural elements in segmental bridge construction. The tendons are composed of high-density polyethylene ducts that contain high-strength steel strands surrounded by cementicious grout. A proof of concept was demonstrated by experiments performed on tendons with passive and corroded strands and through finite-element simulations of the indirect impedance response. Further work showed that bipolar impedance was sensitive to local corrosion in field tendons if the measurement is obtained near the corroding region.

This part expands the application of the bipolar impedance method to corrosion monitoring of inhibitor-impregnated post-tensioned tendon sections. A corrosion inhibitor that is injected into the tendons through the interstitial space of the strands may be capable of preventing or stopping corrosion. The sensitivity of bipolar impedance measurements to changes in grout conductivity and corrosion rate of the steel is assessed by comparison to traditional measurements of the impedance in which direct contact is made to the steel. Additionally, further assessment of the bipolar impedance method is made by relating the analysis results to the actual corrosion damage obtained by autopsies of the tendon sections.

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