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.

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.

Engineers have a range of sophisticated techniques at their disposal to evaluate the condition of reinforced concrete structures and non-destructive evaluation plays a key part in assessing and prioritising where money should be spent on repair or replacement of structurally deficient reinforced concrete structures. Non-destructive evaluation of reinforced concrete structures, Volume 2: Non-destructive testing methods reviews the latest non-destructive testing techniques for reinforced concrete structures and how they are used. Part one discusses planning and implementing non-destructive testing of reinforced concrete structures with chapters on non-destructive testing methods for building diagnosis, development of automated NDE systems, structural health monitoring systems and data fusion. Part two reviews individual non-destructive testing techniques including wireless monitoring, electromagnetic and acoustic-elastic waves, laser-induced breakdown spectroscopy, acoustic emission evaluation, magnetic flux leakage, electrical resistivity, capacimetry, measuring the corrosion rate (polarization resistance) and the corrosion potential of reinforced concrete structures, ground penetrating radar, radar tomography, active thermography, nuclear magnetic resonance imaging, stress wave propagation, impact-echo, surface and guided wave techniques and ultrasonics. Part three covers case studies including inspection of concrete retaining walls using ground penetrating radar, acoustic emission and impact echo techniques and using ground penetrating radar to assess an eight-span post-tensioned viaduct. With its distinguished editor and international team of contributors, Non-destructive evaluation of reinforced concrete structures, Volume 2: Non-destructive testing methods is a standard reference for civil and structural engineers as well as those concerned with making decisions regarding the safety of reinforced concrete structures. Reviews the latest non-destructive testing (NDT) techniques and how they are used in practice Explores the process of planning a non-destructive program features strategies for the application of NDT testing A specific section outlines significant advances in individual NDT techniques and features wireless monitoring and electromagnetic and acoustic-elastic wave technology

Reinforced concrete has the potential to be very durable and capable of withstanding a variety of adverse environmental conditions. However, failures in the structures do still occur as a result of premature reinforcement corrosion. In this authoritative book the fundamental aspects of this complex process are analysed; focusing on corrosion of the reinforcing steel, and looking particularly, at new scientific and technological developments. Monitoring techniques, including the newly developed online-monitoring, are examined, as well as the numerical methods used to simulate corrosion and perform parameter studies. The influence of composition and microstructure of concrete on corrosion behaviour is explored. The second half of the book, which deals with corrosion prevention methods, starts with a discussion on stainless steels as reinforcement materials. There are comprehensive reviews of the use of surface treatments and coatings, of the application of corrosion inhibitors and of the application of electrochemical techniques. In each case the necessary scientific fundamentals are explained and practical instances of use are looked at. This is an invaluable guide for engineers, materials scientists and researchers in the field of structural concrete. Fundamental aspects of corrosion in concrete are analysed in detail Explores how to minimise the effects of corrosion in concrete Invaluable guide for engineers, materials scientists and researchers in the field of structural concrete

A comprehensive text to the non-destructive evaluation of degradation of materials due to environment that takes an interdisciplinary approach Non-Destructive Evaluation of Corrosion and Corrosion-assisted Cracking is an important resource that covers the critical interdisciplinary topic of non-destructive evaluation of degradation of materials due to environment. The authors—noted experts in the field—offer an overview of the wide-variety of approaches to non-destructive evaluation and various types of corrosion. The text is filled with instructive case studies from a range of industries including aerospace, energy, defense, and processing. The authors review the most common non-destructive evaluation techniques that are applied in both research and industry in order to evaluate the properties and more importantly degradation of materials components or systems without causing damage. Ultrasonic, radiographic, thermographic, electromagnetic, and optical are some of the methods explored in the book. This important text: Offers a groundbreaking interdisciplinary approach to of non-destructive evaluation of corrosion and corrosion-assisted cracking Discusses techniques for non-destructive evaluation and various types of corrosion Includes information on the application of a variety of techniques as well as specific case studies Contains information targeting industries such as aerospace, energy, processing Presents information from leading researchers and technologists in both non-destructive evaluation and corrosion Written for life assessment and maintenance personnel involved in quality control, failure analysis, and R&D, Non-Destructive Evaluation of Corrosion and Corrosion-assisted Cracking is an essential interdisciplinary guide to the topic.