Glenn Washer

Health monitoring of civil infrastructures

Reliable health monitoring, including nondestructive evaluation, is an essential part of the feedback and monitoring system for infrastructures. The goal of this paper is to provide a summary of recent research activities that will act as a catalyst to expand interest in the development of new health monitoring technologies. The paper describes the motivation for developing innovative tools for monitoring the health of the USAs infrastructure. An overview of initiatives sponsored by the National Science Foundation to develop new technologies is presented. The paper includes a review of the state-of-the-art stress-wave methods for the evaluation of structural materials and pavements at the National Institute of Standards and Technology. Finally, efforts at the Federal Highway Administration to develop new technologies for the assessment of the nearly 500 000 bridges along the USAs roads and highways are described.

A comparison of nondestructive evaluation methods for bridge deck assessment

Concrete bridge deck deterioration is a significant problem that must be addressed to preserve highway infrastructure investments in bridges around the world. Reducing the cost of bridge deck maintenance is critical to government and private agencies responsible for maintenance of bridges. Maintenance challenges increase as many bridges begin to approach the end of their design life and traffic loads continue to increase. One means of reducing the cost of bridge deck maintenance is to accurately evaluate the condition of the structure and its constituent materials. Current methods used to evaluate deterioration of bridge decks include acoustic, electrochemical, electromagnetic, and visual inspection techniques. The purpose of this study was to assess the advantages and limitations of three available evaluation methods. The evaluation techniques included in this study were ground penetrating radar, the chain drag method, and IE. These techniques represent an important group of inspection methods currently used to evaluate in-service bridge decks. The bridge deck used in the study contains significant delaminations but exhibits virtually no outwardly visible signs of these deficiencies, so a detailed visual inspection survey of the deck was not included. Cores were taken from the bridge deck at selected locations to confirm the accuracy of the results obtained through each evaluation method. This paper presents the findings from each method and describes their respective advantages and limitations.

Visual Inspection of Highway Bridges

The Federal Highway Administration recently conducted an investigation to assess the reliability of visual inspection of highway bridges as implemented by state departments of transportation. The study focused on routine and in-depth inspection, the two most prevalent forms of visual inspection of bridges. Because visual inspection is a highly subjective nondestructive evaluation technique, the results of these bridge inspections can be highly variable and are dependent on many factors. This study included the completion of 10 bridge inspection tasks by 49 practicing state bridge inspectors. With regard to routine inspections, this study showed that condition ratings are assigned with significant variability. Specifically, approximately 68% of condition ratings are within 1 rating point of the average. The results of the in-depth superstructure inspections indicated that these inspections are not likely to detect and identify the specific types of defects for which this inspection procedure is sometimes prescribed. Specifically, widespread defects such as those normally noted during a routine inspection are likely to be noted; however, local deficiencies, such as crack indications, are unlikely to be detected. The results of the deck delamination survey indicate that the accuracy of this type of inspection is relatively poor, with few inspection teams providing results that could be considered to accurately portray the condition of the deck.

Highway Bridge Inspection: State-of-the-Practice Survey

The congressionally mandated National Bridge Inspection Program requires states to inspect periodically all highway bridges on public roads, among other activities; visual inspection (VI) is the primary tool used to perform these inspections. A survey was conducted to help determine current policies and practices that may affect the accuracy and reliability of VI. The survey had three main objectives: to compile a “state of the practice” for bridge inspection, particularly as it pertains to VI; to gather information about bridge inspection management to study how inspection management may influence the reliability of inspections; and to gather data about the current use of nondestructive evaluation technologies and to identify current and future research needs. State departments of transportation, local departments of transportation, and select bridge inspection contractors participated in the survey. Conclusions drawn from this study indicate that the use of nondestructive evaluation has increased since 1993 and that the use of American Society of Nondestructive Testing Level III–certified personnel is increasing. VI was cited as the most frequently used nondestructive evaluation technique; however, vision testing for inspectors is almost nonexistent. Typically, professional engineers were not on site for inspections. State departments of transportation indicated a large demand for future research into the nondestructive evaluation of prestressed concrete superstructures and concrete decks.

Developments for the non-destructive evaluation of highway bridges in the USA

Abstract The collapse of the Silver Bridge in Point Pleasant, West Virginia, in 1967 initiated the formal requirements for the inspection of highway bridges in the USA. Almost 30 years later, visual inspection remains the primary method of bridge inspection. However, many new and promising techniques for the nondestructive evaluation (NDE) of highway bridges have emerged in recent years through the NDE research program of the Federal Highway Administration (FHWA). These include infrared and radar imaging systems, portable ultrasonic systems, telemetry systems, laser deflection measurement systems, and many others. This paper discusses the recent development of these instruments, and the potential impact it may have on bridge inspection and bridge management systems. The paper also discusses the need for validation of system performance, and the FHWA plans to construct a national center for NDE validation at the Turner Fairbank Highway Research Center.

Ultrasonic testing of reactive powder concrete

Concrete is a critical material for the construction of infrastructure facilities throughout the world. Traditional concretes consist of cement paste and aggregates ranging in size from 6 to 25 mm that form a heterogeneous material with substantial compressive strength and a very low tensile strength. Steel reinforcement is used to provide tensile strength for reinforced concrete structures and as a composite the material is useful for structural applications. A new material known as reactive powder concrete (RPC) is becoming available. It differs significantly from traditional concrete; RPC has no large aggregates, and contains small steel fibers that provide additional strength and, in some cases, can replace traditional steel reinforcement. Due to its high density and lack of aggregates, ultrasonic inspections at frequencies 10 to 20 times that of traditional concrete inspections are possible. This paper reports on the initial findings of research conducted to determine the applicability of ultrasonic testing techniques for the condition assessment of RPC. Pulse velocities for shear and longitudinal waves and ultrasonic measurement of the modulus of elasticity for RPC are reported. Ultrasonic crack detection for RPC also is investigated.

Effects of Solar Loading on Infrared Imaging of Subsurface Features in Concrete

This paper addresses the effect of solar loading on thermal imaging for the detection of subsurface deterioration in concrete bridge components. The deterioration of the concrete resulting from corrosion of embedded mild reinforcing and prestressing steel results in delamination and spalling that can affect the strength and serviceability of a concrete structure. The ability to detect this deterioration during its early stages, when mitigation efforts can be employed, can provide a useful tool for maintenance and inspection personnel. Infrared thermography is a tool that has the potential to detect these subsurface defects to compliment inspection efforts and provide an additional means of condition assessment for a bridge. However, the technique relies on thermal gradients developing in the concrete such that a temperature contrast exists between damaged concrete and sound concrete. The environmental conditions at the bridge, such as direct solar loading, ambient temperature variation, and wind affect the thermal gradient in the concrete, and hence, the ability to image subsurface features. The effects of direct solar loading on the detection of subsurface targets in a concrete test block have been studied. Quantitative measurements of the thermal contrast that appear in thermal images of the test block are reported and analyzed. The effect of the depth of the embedded target is discussed, as well as the timing of inspection (relative to sunrise) that resulted in maximum contrast in thermal images.

Effects of Environmental Variables on Infrared Imaging of Subsurface Features of Concrete Bridges

Deterioration of concrete due to corrosion of embedded steel reinforcing bars and prestressing strands represents a significant challenge for inspection and maintenance engineers. Delaminations develop in the concrete manifest as spalling, which further exposes the steel to the corrosive environment and accelerates the deterioration process. The typical method for detecting these delaminations is hammer sounding, which requires hands-on access to the material under inspection. Specialized equipment and lane closures are frequently necessary to achieve the required access. Application of infrared imaging to detect the subsurface features in concrete can image such defects from a distance, such that direct access to the surface of the concrete is not required. However, the method relies on environmental conditions to create thermal gradients in the concrete so that these subsurface features can be detected. A study examined the optimum environmental conditions for detection of subsurface features in concrete. The goal was to provide guidance on the practical application of infrared imaging for inspection of concrete bridge components. The effects of solar loading from direct sunlight and wind speed have been examined to determine their impact on the detectability of subsurface features in concrete. The optimum time of day for detection of subsurface defects and the effect of their depth is discussed. Characteristics of optimum inspection conditions for using infrared cameras in the field are described.

Guidelines for Thermographic Inspection of Concrete Bridge Components in Shaded Conditions

Infrared thermography has the potential to detect subsurface delaminations before spalling develops and could be used to improve the visual inspection of concrete bridges. The technology has traditionally been applied to bridge decks, which are exposed to radiant heating from the sun that helps develop the necessary thermal gradients in the concrete. Thermal gradients can also be developed from normal diurnal temperature variations. Convective heat transfer develops the thermal gradients, although these thermal gradients are of much lower magnitude than those developed through radiant heating from the sun. This paper presents the results of a study to develop thermal imaging for the detection of subsurface deterioration in the soffit areas of bridges; these soffit areas are shaded and therefore are not exposed to radiant heating from the sun. Experimental studies and field testing were conducted and are described. This paper reports on guidelines developed for this application of the technology; the guidelines address the necessary environmental conditions to enable the detection of damage in bridge soffit areas. Specifically, the paper discusses the rates of change in ambient temperature needed to ensure that subsurface damage can be detected in shaded conditions. The paper also discusses the effect of wind speed on the detectability of subsurface damage in the shaded areas of a bridge, as well as the camera settings needed to ensure that an inspector can detect temperature anomalies associated with subsurface damage. A field example is provided to illustrate the application of the technology and highlight the required camera settings.

Raman Spectroscopy for the Nondestructive Testing of Carbon Fiber

The goal of this research is to evaluate the potential of Raman spectroscopy as a method of condition assessment for carbon fiber composite materials used in high performance situations such as composite overwrapped pressure vessels (COPVs). There are currently limited nondestructive evaluation (NDE) technologies to evaluate these composite materials in situ. Variations in elastic strain in the composite material can manifest from degradation or damage, and as such could provide a tool for condition assessment. The characterization of active Raman bands and the strain sensitivity of these bands for commercially available carbon fibers are reported.