Graduation Year

2007

Document Type

Thesis

Degree

M.S.M.E.

Degree Granting Department

Mechanical Engineering

Major Professor

Alberto A. Sagüés, Ph.D.

Keywords

Tendon anchorage, Non destructive methods, Corrosion monitoring, Probes, Electrochemical Impedance Spectroscopy, Linear Polarization

Abstract

Severe corrosion damage and even complete failure was recently discovered in external post-tensioned (PT) tendons of three Florida's pre-cast, segmental bridges over seawater. A key deterioration factor was the formation of large bleed water grout voids at or near the anchorages. Steel corrosion may occur at the grout-void interface or in the air space of the void itself. Since the tendons are critical to the structural integrity of the bridges, reliable and non-intrusive damage detection methods are desirable to manage or prevent future occurrences. In recent years several indirect non-destructive methods have been developed or improved to evaluate the conditions of the tendons. One of those methods is vibration-based tension measurements, consisting of detecting tendon tension loss by analyzing the tendon's natural frequencies.

Until recently, vibration-based tension measurements were costly and laborious since they required several operators to conduct the tests and complicated analysis through different programs. The first objective of this research is to provide a practical, simplified, user-friendly testing and analysis method for screening tendons by vibration measurements. Electrochemical Impedance Spectroscopy, Linear Polarization, and Electrical Resistance are alternative methods that could nondestructively detect or monitor corrosion before strand failures occur. The reliability and sensitivity of these conventional monitoring methods in solid or liquid media are well proven. However, few investigations exist on applying these methods to air-space corrosion as it may occur in tendon anchors. The second objective of this research is to establish the feasibility of using the above conventional monitoring methods for detecting air-space corrosion.

In this investigation, two different types of Electrical Resistance probes were designed and evaluated. Also, electrochemical probes were constructed simulating strands conditions in the grout-void interface. Electrochemical Impedance Spectroscopy and Linear Polarization measurements were conducted in the electrochemical probes to calculate their instantaneous corrosion rates. Electrical Resistance and Electrochemical probes results indicate that both methods provide sufficient sensibility to determine the ongoing damage.

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