Graduate Studies, UNL

 

Dissertations and Doctoral Documents from University of Nebraska-Lincoln, 2023–

First Advisor

Jiong Hu

Degree Name

Doctor of Philosophy (Ph.D.)

Committee Members

George Morcous, Jinying Zhu

Department

Civil Engineering

Date of this Version

2025

Document Type

Dissertation

Citation

A dissertation presented to the faculty of the Graduate College of the University of Nebraska in partial fulfillment of requirements for the degree Doctor of Philosophy (Ph.D.)

Major: Civil Engineering

Under the supervision of Professor

Lincoln, Nebraska, December 2025

Comments

Copyright 2025, the author. Used by permission

Abstract

Premature failure of prestressed and post-tensioned concrete structures is frequently caused by undetected corrosion of prestressing steel. Although extensive research has addressed corrosion rates in conventionally reinforced concrete, the interpretation of non-destructive parameters, such as half-cell potential (HCP) and concrete/grout resistivity, for estimating corrosion rates in prestressing steel are not adequately investigated.

This research experimentally evaluates chloride-induced corrosion of prestressing steels to establish material-specific relationships between in-situ measurable parameters and corrosion rate. Thirty-six macrocell specimens incorporating plain wires, indented wires, and seven-wire strands in structural concrete and commercial post-tensioning grout- half with pre-formed surface cracks, were subjected to accelerated cyclic wetting with 3 % NaCl solution and drying. Macrocell current, HCP, and matrix resistivity were monitored continuously, while post-exposure forensic examination quantified localized damage and validated the non-destructive measurements.

Key findings reveal that strand geometry and grout microstructure accelerate corrosion. Microcell corrosion accounts for the majority of material loss, indicating that macrocell current measurement alone is unconservative. Corrosion propagation initiated abruptly at around 10 μm/year, followed by exponential acceleration under cyclic moisture exposure contradicting traditional models that assume decelerating rates due to drying of concrete. Robust empirical relationships between corrosion rate and matrix resistivity have been developed that physically capture the transition from ohmic/anodic to diffusion/cathodic control mechanism enabling quantitative corrosion rate estimation from routine field resistivity measurements. In contrast, HCP exhibited only qualitative correlation with corrosion rate, but material-specific thresholds were established: high corrosion (>10 μm/year) corresponds to HCP < −450 mV/CSE and resistivity < 600 k·cm in grout versus < −250 mV/CSE and < 450 kΩ·cm in concrete. A linear correlation between HCP and material resistivity has been developed to further aid engineers in in situ measurements and interpretation.

The study provides experimentally validated, prestressing steel-specific corrosion rate models and interpretation protocols. Practical field guidelines and risk classification tables for resistivity and HCP tailored to strands in grout and concrete are proposed, which are expected to significantly improve the reliability of condition assessment in prestressed and post-tensioned structures, enabling proactive maintenance before catastrophic failure.

Advisor: Jiong Hu

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