Corrosion of reinforcing steel bars (rebar) in reinforced concrete decks can lead to serious structural issues in bridges. Ultrasonic Testing (UT) methods provide small wavelengths that can be used for early detection of several types of deterioration. The recently-developed Ultrasonic Guided Wave Leakage (UGWL) Method utilizes steel as the waveguide and measures the energy leaked into the surrounding concrete. Previous studies completed at University of NebraskaLincoln demonstrated that the measurements of the leaked energy using receivers from the concrete surface can successfully identify early stages of various flaws such as corrosion, delamination, and cracking. In this method, the longitudinal waves are generated along the rebar by a transmitter placed directly on the rebar, and recorded by an array of receivers on the concrete surface. Previous studies have shown promise in testing stretches of concrete decks as long as 10 feet using a single transmitter and an array of sensors placed 6 inches apart. The primary goal of this Master's thesis is to demonstrate that the recently developed UGWL method has several advantages over the commonly used Half-Cell Potential (HCP) method in the detection of corrosion in reinforced concrete (RC) bridge decks. To achieve this goal, laboratory experiments as well as a pros-and-cons analysis is conducted. Laboratory specimens are placed in a corrosive environment by submerging them in 10% NaCl solution. These slabs were then monitored for 6 months. During this period, UGWL and half-cell potential data were collected every 6 days. After testing was completed, chloride threshold levels (CTLs) were measured on cores taken from the specimens. The secondary goal of this thesis is to develop a quantitative correlation between UGWL data and CTLs, similar to those established between HCP and CTLs in the literature. The experimental results demonstrated that the UGWL technique detected the corrosion activity approximately 21 days sooner than the HCP method. The findings also suggest that chloride content determined after the completion of the corrosion process, which lasted for 6 months, exceeded the standard chloride threshold levels; confirming that the selected method of inducing corrosion in the lab was successful.

Half cell mapping has for at least fifteen years been the most popular non-destructive methods of investigating the corrosion state of embedded reinforcement. However, although this method is becoming widely used in civil engineering for determining the corrosion state of the steel reinforcement in concrete, there has been very little consideration of the principles and potential measurement. This practical guide explains the principles of potential measurement, shows how these should be undertaken and, most critically, provide ways of interpreting the data.

The proposed study explores the feasibility of detecting and quantifying corrosion and delamination (physical separation) at the interface between reinforcing steel bars and concrete using ultrasonic guided waves. The problem of corrosion of the reinforcing steel in structures has increased significantly in recent years. The emergence of this type of concrete deterioration, which was first observed in marine structures and chemical manufacturing plants, coincided with the increased applications of deicing salts (sodium and calcium chlorides) to roads and bridges during winter months in those states where ice and snow are of major concern. Concrete is strengthened by the inclusion of the reinforcement steel such as deformed or corrugated steel bars. Bonding between the two materials plays a vital role in maximizing performance capacity of the structural members. Durability of the structure is of concern when it is exposed to aggressive environments. Corrosion of reinforcing steel has led to premature deterioration of many concrete members before their design life is attained. It is therefore, important to be able to detect and measure the level of corrosion in reinforcing steel or delamination at the interface. The development and implementation of damage detection strategies, and the continuous health assessment of concrete structures then become a matter of utmost importance. The ultimate goal of this research is to develop a nondestructive testing technique to quantify the amount of corrosion in the reinforcing steel. The guided mechanical wave approach has been explored towards the development of such methodology. The use of an embedded ultrasonic network for monitoring corrosion in real structures is feasible due to its simplicity. The ultrasonic waves, specifically cylindrical guided waves can propagate a long distance along the reinforcing steel bars and are found to be sensitive to the interface conditions between steel bars and concrete. Ultrasonic transducers are used to launch and detect cylindrical guided waves along the steel bar. In this dissertation, in-situ corrosion monitoring technique for reinforced concrete is developed based on two methods - 1) variation of signal strength and 2) the time-of-flight (TOF) variations as the corroded member is loaded transversely. This is the first attempt ever to monitor corrosion inside concrete by measuring the change in the time of flight of guided waves along reinforcing bars as the concrete beam is subjected to bending. Advantages of corrosion monitoring by TOF change are discussed in the dissertation.

"A review is presented of nondestructive test (NDT) methods for evaluating the condition of concrete and steel reinforcement in structures. Methods discussed include visual inspection, stress-wave, nuclear, measurement of fluid transport properties, magnetic and electrical, infrared thermography, and ground-penetrating radar. The principle of each method is discussed and the typical instrumentation described. Testing procedures are summarized and the data analysis methods explained. The advantages and limitations of the methods are highlighted. This report concludes with a discussion of planning a NDT program. General information is provided for those faced with the tast of evaluating the condition of a concrete structure and who are considering the applicability of NDT methods to aid in that evaluation."--p. 1.

Understanding and recognising failure mechanisms in concrete is a fundamental pre-requisite to determining the type of repair, or whether a repair is feasible. This title provides a review of concrete deterioration and damage, as well as looking at the problem of defects in concrete. It also discusses condition assessment and repair techniques. Part one discusses failure mechanisms in concrete and covers topics such as causes and mechanisms of deterioration in reinforced concrete, types of damage in concrete structures, types and causes of cracking and condition assessment of concrete structures. Part two reviews the repair of concrete structures with coverage of themes such as standards and guidelines for repairing concrete structures, methods of crack repair, repair materials, bonded concrete overlays, repairing and retrofitting concrete structures with fiber-reinforced polymers, patching deteriorated concrete structures and durability of repaired concrete. With its distinguished editor and international team of contributors, Failure and repair of concrete structures is a standard reference for civil engineers, architects and anyone working in the construction sector, as well as those concerned with ensuring the safety of concrete structures. Provides a review of concrete deterioration and damage Discusses condition assessment and repair techniques, standards and guidelines

This authoritative book provides a comprehensive review of the highly important subject of non-destructive evaluation of reinforced concrete structures. Engineers have a range of sophisticated techniques at their disposal to assess the condition of reinforced concrete structures that do not cause material damage and which usually enable the structure to be used while the surveys are carried out. Non-destructive evaluation of the infrastructure also plays a key role in calculating and prioritising where money should be spent on repair or replacement. Providing details of related techniques and case studies, this book offers an overview of how to plan and implement the NDT of reinforced concrete structures.