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Nondestructive Evaluation Laboratory



The Federal Highway Administration’s (FHWA’s) Advanced Sensing Technology (FAST) NDE Laboratory houses state-of-the-art NDE equipment to support FHWA’s strategic vision and to provide training to stakeholders who maintain and manage transportation infrastructure such as bridges, pavements, tunnels, and ancillary structures. Using NDE tools and equipment, the NDE Laboratory works side by side with FHWA’s research programs, such as the Long-Term Bridge Performance Program. Some of the equipment is described below. The equipment is sorted into groups based on concrete or steel application.

Equipment for Concrete | Equipment for Steel

Equipment for Concrete

Concrete: Electrical Resistivity (ER)

One of the most effective ways to assess the susceptibility of a reinforced concrete element to corrosion is by measuring concrete surface resistivity. Low concrete resistivity is an indication of an environment supporting corrosion processes and typically leads to high corrosion rates. Measurement of resistivity is most commonly done using a four electrode probe, the Wenner probe (figure 1), which is simply pressed against a damp surface of an element and the displayed resistivity recorded. For more information about this technology available in the NDE Laboratory, visit the Electrical Resistivity page on the FHWA NDE Web Manual.

There are two photographs in this figure. The left photo shows one side of a small rectangular meter labelled “resipad proceq” with a wrist strap attached to the right end. The right photo shows the meter in an upright position, with four probes resting on a table. A cable runs from the left end of the meter to an unidentified thin black apparatus.
Figure 1. Photographs. Concrete Electrical Resistivity Meter.


Concrete: Galvanostatic Pulse Measurement (GPM)

The “corrosion rate” refers to the speed with which steel reinforcement corrodes. Rapid and nondestructive estimations of the corrosion rate can be performed using the GPM. The effectiveness of the method stems from its active nature, i.e., the ability to polarize rebars through the induction of small current pulses and then measure the changes of the electrochemical potential. A GPM device is available at the NDE laboratory (figure 2). For more information, visit the GPM technology page on the FHWA NDE Web Manual.

This figure is composed of three photographs. The largest, central photo displays a worker in a yellow safety vest and orange helmet kneeling on one knee on a concrete deck. In the worker’s left hand is an instrument with a key pad and display screen, while the worker is placing a probe on the deck with his right hand. Two inset photos provide close-ups of the instrument and probe, respectively.
Figure 2. Photographs. Galvanostatic Pulse Measurement (GPM).

Concrete: Ground Penetrating Radar (GPR)

GPR is an NDE technology that can be used in the assessment of many infrastructure assets. GPR is used in the assessment of corrosion-induced deterioration; mapping of reinforcement; and thus, measurement of concrete cover; identification of layers; and measurement of their thickness in multilayer structures, such as pavements, detection of voids, etc. One of the main advantages of GPR is the speed of data collection. Detectability of features and deterioration greatly depends on the size, depth, and dielectric properties of the structure. Therefore, GPR systems with antennas of different frequencies and power (figure 3 through figure 6) need to be used in different applications. The laboratory houses multiple GPR equipment with various specifications. For more information, visit the GPR technology page on the FHWA NDE Web Manual.

A small four-wheeled yellow vehicle is attached by a cable to a rectangular instrument with a display screen, which resembles a tablet.
Figure 3. Photograph. GPR System, MALA, CX-11.

A small two wheeled yellow vehicle-like device is attached by a cable to a yellow rectangular instrument with a display screen.
Figure 4. Photograph. GPR System, Sensors, and Software, Conquest.

There are two photographs in this figure. The left photograph consists of a small four-wheeled vehicle attached by a cable to a small black box. Next to the vehicle is a rectangular device with a display screen and various buttons. The device is not connected to the small vehicle or its accompanying black box. The right photograph is an orange rectangular instrument with a long yellow handle extending diagonally upward to the right. The rectangular device from the left image is to the rear of the long handled instrument.
Figure 5. Photographs. GSSI GPR System with
1.6 GHz (Left) and 900 MHz (Right) Antenna.


This figure is a photograph of a four-wheeled cart with a central orange box. A black handle extends from the right end of the cart diagonally upward to the right.
Figure 6. Photograph. Cart with a GPR antenna.

Concrete: Half-Cell Potential (HCP)

Corrosion is an electrochemical process in which a corroding rebar generates an electrical field. The HCP enables the measurement of the potential of that field, by connecting the half-cell probe (reference electrode) to the rebar through a high impedance voltmeter. The stronger negative- measured voltage will have a higher probability of active corrosion. HCP can be used on any reinforced concrete structure where a connection to the reinforcement can be made, and where there is no electrically isolating surface layer. Depending on the application, different types of probes, such as copper, copper sulphate rod, or rolling electrode, may be used. An HCP analyzing instrument with a rolling probe, which is used for the rapid scanning of large areas, is available at the NDE Laboratory (figure 7). For more information, visit the HCP page on the FHWA NDE Web Manual.

This photograph is composed of two instruments. To the left is a rectangular blue instrument with a small display screen and a limited key pad. On the right is a small cylindrical device. The top of the device is blue, while the bottom is white.
Figure 7. Photograph. Half-Cell Potential (HCP)
Corrosion Analyzing Instrument and Probe.

Concrete: Impulse Response (IR)

IR is a method that examines the dynamic response of an element or structure in order to identify the presence of anomalies. It has been used as a screening tool for the detection of voids, loss of support, or presence of large delamination or debonding. The IR measurement method involves striking the surface of an object using an instrumented hammer, and measuring the response with a nearby transducer, typically a geophone (velocity transducer), to generate mobility spectra. Multiple parameters can be extracted from mobility plots, such as dynamic stiffness, average mobility, and mobility slope, which are used in the interpretation of the measurement results (figure 8). An IR set is available at the NDE Laboratory.

A hammer-like device is positioned in the foreground along with a small red box. A laptop is positioned on top of a black box is in the background. The black box has 2 knobs, 2 status lights, and an on/off switch. The hammer has a spiral coiled cable connected to the end of the handle, however the other cable end is not connected in this image. The small red box has a cabled coil connected to its right side, ending in a blue plug. The plug is not connected in this image.
Figure 8. Photograph. Impulse Response (IR) Testing System.

Concrete: Infrared Thermography (IRT)

IRT is used to detect defects, most commonly delamination, in structures by measuring the surface temperature variations as a result of uneven heating and cooling in the vicinity of defects. The IRT camera has thermal fusion functionality, which allows easier identification and interpretation of infrared images. The camera has an infrared (IR) resolution of 320 by 240 pixels, with video capabilities (figure 9). Two models of IRT are available at the NDE Laboratory. For more details about this technology visit the IR page on the FHWA Web Manual.

This photograph consists of a specialized digital camera. The digital display is facing the viewer and has five control buttons. On the left rear side of the camera is a cylindrical piece. On the right is a hand strap. The cameras controls are in the upper right portion of the camera.
Figure 9. Photograph. Infrared Thermography Camera.

Concrete: Ultrasonic Pulse Echo (UPE)

The UPE method is primarily used to inspect the interior portions of the concrete structural members and tunnel linings to detect voids, delamination, and debonding; assess the grouting condition in post-tensioning ducts, and to measure thickness of members, etc. The UPE test involves emitting ultrasonic waves into the element, and recording the reflections from the objects and interfaces between the materials of different acoustic impedances. The concrete UPE application differs from traditional steel applications in two ways. The first is the use of low- frequency transducers, and the second is that the test is conducted with transducers placed in dry contact, i.e., without a couplant.

UPE equipment is available in different sizes, varying from two transducers used to conduct simple point measurements to a large number of transducers in an array arrangement used to conduct tomographic measurements. Two different models of UPE are available at the NDE laboratory (figure 10). For more information about this technology, visit the UPE page on the FHWA NDE Web Manual.

This figure consists of two photographs. A control and recording rectangular instrument is in the left photograph. It has a central display screen with control panels on either side. Two handles placed over the control panels extend from the instrument into the foreground. The photograph on the right is of a rectangular instrument. The face of the instrument has twenty-four transducers arranged in an array that is six transducers wide and four transducers high.
Figure 10. Photographs. Ultrasonic Pulse Echo (UPE) system.


Concrete: Ultrasonic Surface Waves (USW)

The USW technique is primarily used to assess the quality of concrete through the measurement of concrete modulus. The method can also indirectly detect the presence of delamination, voids, and other major anomalies in the element. The USW test involves the measurement of the transient response of the deck to an impact by a receiver pair. The recorded response is analyzed to provide the velocity of surface waves, which can be directly correlated to the concrete modulus (figure 11). For more information about this technology, visit the USW page on the FHWA NDE Web Manual.

A laptop computer is positioned in the right foreground of the photograph. It is connected by a cable to a device with a pair of cylindrical probes on the left end of the device and an instrument box on the right end. The device is positioned behind and to the left of the laptop.
Figure 11. Photograph. Ultrasonic Surface Waves (USW) Testing System.

Equipment for Steel

Steel: Acoustic Emission (AE)

AE technology is typically applied to steel bridge elements, such as steel girders, truss members, pin assemblies, and eyebars, to monitor existing cracks, detect the development of new cracks, or to monitor a retrofit that was intended to arrest crack expansion or stop new fatigue cracks from developing. The AE sensors, with an operating range of 70 kHz to 200 kHz, detects transient elastic waves generated by sudden bursts of energy as a result of crack development or growth. The method can be used to both locate and characterize the source. An AE data acquisition system with a flexible sensor fusion interface for input and processing of a variety of sensors is available at the NDE Laboratory. The system is designed for outdoor environments and has the ability to transmit data wirelessly to a remote location. The system uses a dedicated software package for AE data acquisition (figure 12), data visualization, and health monitoring. For more information about this technology, visit the AE page on the FHWA NDE Web Manual.

The right-opening door to a rectangular metal box is open, revealing circuits, cables, and computer-like electronics that constitute the system.
Figure 12. Photograph. Acoustic Emission Data Acquisition System.

Steel: Eddy Current Testing (ECT)

ECT is used to detect cracks and pitting in steel bridge members. Due to the magnetic properties of steel, only surface or near surface-breaking cracks can be detected. The technology can be effective for detecting cracks in welds; however, special probes must be used due to complex magnetic and microstructural properties associated with the weld and the surrounding heat- affected zone (HAZ). ECT works by scanning a small electromagnetic probe across the surface of a material with an objective to detect changes in eddy currents. The changes are a result of the presence of defects or changes in material properties of the tested object, electrical conductivity, and particularly magnetic permeability. Conventional handheld eddy current systems with absolute and differential point probes that have an operating frequency of 50 Hz to 12 MHz are available for use in the inspection of surface defects in metals. Two models of ECT equipment are available at the NDE Laboratory: conventional and advanced (figure 13). For more information about this technology, visit the ECT page on the FHWA NDE Web Manual.

The small black instrument is roughly rectangular with a display screen on the upper half and a small keypad on the lower half. A cable is plugged into the top and in the foreground the cable is connected to a small probe. A rear-mounted hand strap can be seen in the photo.
Figure 13. Photograph. Eddy Current Testing (ECT) instrument.

Steel: Eddy Current Array (ECA) Testing

ECA has several advantages over ECT, such as better detection capabilities, faster inspection, and easier data analysis and interpretation. This is a result of using multiple coils to generate eddy currents arranged in specific patterns. The advanced eddy current system is an impedance instrument with a 37-channel probe electronics unit and a high-frequency eddy current array (figure 14). The eddy current array has a drive winding with linear drive segments, and is excited with a current at a prescribed frequency. The frequency range is from less than 1kHz to 40 MHz, which provides a desired spatial distribution for the imposed magnetic field. Significant changes in the signal’s magnetic permeability readings will indicate the presence of a flaw in the material. For more information about this technology, visit the ECA page on the FHWA NDE Web Manual.

A small rectangular instrument is placed on top of a larger piece of electronics. The small component is attached to the larger component by a thin light grey cable, and a thick dark grey cable which splits into three plugs.
Figure 14. Photograph. Eddy Current Array Testing System.

Steel: Portable Phased Array Ultrasonics (PAUT)

PAUT can be applied to detect flaws, cracks, and weld flaws in steel bridge members. It can also be used for element thickness measurements. PAUT uses an array of ultrasonic transducers that are pulsed independently to create wave patterns that target specific locations. The beam from a phased array probe is moved electronically in all directions, which allows fast scanning of large volumes of a tested object (figure 15). For more information about this technology, visit the PAUT page on the FHWA NDE Web Manual.

The rectangular instrument has a top carrying handle, a large digital screen and two rows of vertically inset buttons to the left and right of the screen. A cable is plugged into the instrument’s upper rear corner and in the forefront it is connected to a silver and black probe.
Figure 15. Photograph. Portable Phased Array Ultrasonic System.

Steel: Ultrasonic Testing (UT)

UT technology can be applied to truss members, steel girders, or other steel bridge components with a plate-like geometry (i.e., parallel surfaces). UT is used to detect cracks and weld flaws, and to determine the thickness or length of a tested member. UT uses a transducer placed on the surface to emit high-frequency acoustic waves into the structure. The waves are reflected from discontinuities in the material, which are then detected by the transducer. The technology is typically implemented using longitudinal (straight beam) or shear wave (angled beam) methods. Longitudinal wave methods are used to detect cracks in bridge pins, trunnion shafts, or eyebars, or measure the thickness of a steel plate in order to detect section loss as a result of corrosion (figure 16). Shear wave methods (angled beam) are commonly used to inspect welds for flaws (figure 17). For more information about this technology, visit the UT page on the FHWA NDE Web Manual.

This photograph consists of two devices. The top device is a hand-held instrument with a small display screen on the upper third of the device and a key pad on remaining device face. The instrument is connected by a cable to a small black box.
Figure 16. Photograph. Ultrasonic Testing (UT) for thickness measurement.

The black instrument is rectangular with an orange frame and consists of a viewing screen with three control buttons. A hand strap is affixed to the left side. A clear plastic probe is positioned in the foreground, with a cable that connects to the left rear of the orange/black device.
Figure 17. Photograph. Ultrasonic Testing (UT) for flaw detection.

Loading Frame and Environmental Testing Chamber

The laboratory is equipped with a 22-kip load frame with an environmental testing chamber. The environmental chamber enables the mechanical testing of materials and components across a broad range of temperature, humidity, and caustic conditions. The equipment is ideal for conducting tension, compression, bending, and cyclic fatigue testing of metals, composites, and ceramics.

X-ray Computed Tomography (CT) and Digital Radiography Imaging System

An X-ray CT and digital radiography imaging system was acquired to accommodate the research needs of the laboratory. The system can assist many applications including materials research, nondestructive testing, core sample characterization, weld inspection, failure analysis, and reverse engineering. The X-ray CT enables the visualization of the interior of scanned objects by directing X-rays at an object from different directions and examining the attenuation or strength of reflections along a series of linear paths. Unlike traditional X-ray imaging, the digital radiography utilizes X-ray sensors to transfer and enhance images digitally. The system has been used by researchers at the NDE Laboratory for various projects, such as the determination of air-void parameters, crack propagation, and internal structure characterization of portland cement concrete and asphalt concrete structures.

Lab-based large specimen scanning systems: xy scanner and robot scanner

Two specimen scanning systems were developed to accommodate high resolution experimental testing performed in the NDE Laboratory.

The xy scanner platform covers an 8-foot by 8-foot scanning area. The scanning head is fitted with a manipulator attachment designed to hold various NDE probes. The scanning head manipulator also provides means for probe orientation, including probe downward/upward positioning, surface contact, predetermined contact pressure, and duration. A scan, using various NDE sensor technologies, can be conducted at the nodal points of a virtual grid with as small as elements as desired. Computer control and data acquisition are available to integrate and automate new sensor technologies into the scanning system. The system is designed to be adaptable to vertical surfaces, such as tunnel walls, as well as horizontal slabs.

Figure 18. Photograph. XY scanner in foreground and robot scanner in background for high volume lab specimen testing.
Figure 18. Photograph. XY scanner in foreground and robot
scanner in background for high volume lab specimen testing.

The robot scanner includes a KUKA KR R110  robot mounted on an external stepper motor controlled x-axis to extend the range of the robot. The robot system includes the KRC4 compact controller with EtherCAT communication implemented to control the external axis. The robot enables high precision, high volume measurement scans across complex surfaces. The robot scanner system is able to automate measurements with legacy via pneumatic actuation.

Figure 19. Photograph. Robot scanner for high volume lab specimen testing.
Figure 19. Photograph. Robot scanner for high volume lab specimen testing.

Portable automated acoustic array

A portable acoustic array for multiple simultaneous impact echo (IE) and ultrasonic surface wave testing (USW) was developed. The system covers a 4-feet-wide testing strip. The array has five sources and eight receivers. The spacing between the impact sources is 12 inches. The sensors and sources are coupled to the surface pneumatically, which enables the array to compensate for uneven surfaces and ensure that all the sources and sensors are coupled to the surface with equal force.

Figure 20. Image. A schematic of the pneumatic acoustic array.
Figure 20. Image. A schematic of the pneumatic acoustic array.

The five source and eight sensor arrangement enables eight IE tests and eight USW tests. The sources are solenoid impactors, while the sensors are accelerometers. The accelerometers cover a frequency range of 100 Hz to 25 kHz. The system is portable for field use.

Figure 21. Photograph. Portable pneumatic acoustic array.
Figure 21. Photograph. Portable pneumatic acoustic array.

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