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Laboratory Equipment

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.

NDE Laboratory Equipment
Equipment for Concrete Equipment for Steel Equipment for Asphalt
Electrical Resistivity (ER)

Eddy Current Testing (ECT)

Density Profiling System (DPS)

Galvanostatic Pulse Measurement (GPM)

Eddy Current Array (ECA) Testing


Ground Penetrating Radar (GPR)

Portable Phased Array Ultrasonics (PAUT)


Half-Cell Potential (HCP)

Ultrasonic Testing (UT)


Impulse Response (IR)

Loading Frame and Environmental Testing Chamber


Infrared Thermography (IRT)

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


Ultrasonic Pulse Echo (UPE)

Lab-Based Large Specimen Scanning Systems: XY Scanner and Robot Scanner


Ultrasonic Surface Waves (USW)

Portable Automated Acoustic Array

Impact Echo (IE)    

AnchorEquipment for Concrete

AnchorConcrete: 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.

"The Four-Point Wenner Probe Concrete Electrical Resistivity Meter with the left part of the front paneldisplay showing the measurement 0L kilo-ohm centimeter."

Top View.

"The side view of Four-Point Wenner Probe Concrete Electrical Resistivity Meter showing four electrodes protrude from the bottom of the casing."

Side View.
Figure 1. Photographs. Four-Point Wenner Probe Concrete Electrical Resistivity Meter.

AnchorConcrete: 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.

"A technician demonstrates the proper operation of the galvanostatic-pulse method. The technician is kneeling on a concrete deck, focused on the display screen in his left hand while pressing the probe to the concrete with his right hand. An inset in the upper right corner of the figure shows a close-up view of the control unit, which has a small display screen and keyboard. Another inset in the lower right corner of the figure shows the probe. The upper part of the probe is a rounded tube that can be grasped by the operator’s hand. Wiring from the control unit enters the upper end of the tube. The bottom of the tube is attached to a large round sponge that, when dampened, allows a pulse from the electrode to enter the concrete."
Figure 2. Photographs. Galvanostatic Pulse Measurement (GPM).

AnchorConcrete: 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 (figures 3 through 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.

"GPR System, Sensors, and Software, Conquest. This photo shows a GPR system from Conquest Company consisting of the sensor antenna on the right side of the photo and the control panel on the left side."
Figure 3. Photograph. GPR System, Sensors, and Software, Conquest.


"Figure 4-A. GSSI GPR System with 1.6 GHz. This photo shows the GPR system including the control panel at the top, the manual antennal cart at the middle and the connector box at the bottom of the photo."


"Figure 4-B. 900 MHz (B) Antenna. This photo shows the GPR system including the control panel at the back and the sensor at the front of the photo. "


Figure 4. Photographs. GSSI GPR System with 1.6 GHz (Left) and 900 MHz (Right) Antenna.

"Figure 5. Proceq Live Wireless GPR antenna with range of 0.9 to 3.5 GHz. This figure shows the wireless GPR system with the tablet in the back showing a B-scan of the data and the manual antenna cart in the front of the photo."
Figure 5. Photograph. Proceq Live Wireless GPR antenna with range of  0.9 to 3.5 GHz.

"Cart with a GPR antenna. This photo shows the mobile walk behind pushing cart that can accommodate the GPR antennas and control panels. "
Figure 6. Photograph. Cart with a GPR antenna.

AnchorConcrete: 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.

"HCP Corrosion Analyzing Instrument and Probe.  This photo shows the HCP gauge which is a blue box with keyboards and LED light-emitting diode screens at the left side. At the right side of the photo, a half-cell potential rolling electrode probe is shown. "
Figure 7. Photograph. Half-Cell Potential (HCP) Corrosion Analyzing Instrument and Probe.

AnchorConcrete: 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.

"Impulse Response (IR) Testing System. This photo is of the impulse response–testing system. A black hammer is lying on the table. A velocity transducer is to the right. A laptop is sitting on top of a data-acquisition box. The hammer and transducer are connected to the data-acquisition system by cables."
Figure 8. Photograph. Impulse Response (IR) Testing System.

AnchorConcrete: 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. IRT cameras have thermal fusion functionality that allows easier identification and interpretation of infrared images. Two models of IRT cameras are available at the NDE Laboratory (figure 8). For more details about this technology visit the IR page on the FHWA Web Manual.

"Infrared Thermography Camera.  This photo shows an infrared camera on a desk. The infrared camera has a light-emitting-diode (LED) screen and control buttons on the back, and a black handle on the right. The lens is located on to the left of the LED screen."
Figure 9. Photograph. Infrared Thermography Camera.

AnchorConcrete: 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 9). For more information about this technology, visit the UPE page on the FHWA NDE Web Manual.


"Ultrasonic tomographer (MIRA).  This photo is a top view of an ultrasonic tomographer (MIRA), showing the LCD liquid-crystal display and control panel of the tomographer. The tomographer is rectangular with two rotating handles mounted near its ends and a LED light-emitting diode screen in the center."

A. Ultrasonic Tomographer (MIRA)

"Ultrasonic Pulse-Echo (EYECON).  This photo is of an ultrasonic pulse echo probe lying on its side, showing the 24 transducers on its bottom surface. The protruding ends of the transducers are cylindrical in shape."

B. Ultrasonic Pulse-Echo (EYECON)

Figure 10. Photographs. Ultrasonic Tomographer System.

AnchorConcrete: 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 10). For more information about this technology, visit the USW page on the FHWA NDE Web Manual.

"USW Testing System.  This photo shows ultrasonic surface wave testing equipment, which has three vertical, cylindrical objects and one metal box, all attached to two large, rounded, horizontal connecting bars. The two cylindrical objects closest to the box are sensors. The third cylindrical object on the right end of the connecting bar is an impact source. Yellow cables run from the metal box to each of the cylindrical objects. A laptop collect all the data with a cable attached to the tool."
Figure 11. Photograph. Ultrasonic Surface Waves (USW) Testing System.

AnchorConcrete: Impact Echo (IE)

The IE method is a seismic or stress wave-based method used to detect defects in concrete, primarily delamination. The objective of the IE survey is to detect and characterize wave reflectors, or resonators, in a concrete bridge deck or other structural elements. The amplitude spectrum obtained from the fast Fourier transform analysis of the time signal will show dominant peaks at certain frequencies that can be interpreted to assess the deck condition. For more information about this technology, visit the IE page on the FHWA NDE Web Manual.

"IE Testing System. This photo shows an impact echo tool on the left and a laptop that collects data on the right. The laptop and the IE tool are connected with a cable. The laptop screen shows a waveform."
Figure 12. Photograph. Impact Echo (IE) Testing System.

AnchorEquipment for Steel

AnchorSteel: 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 12). For more information about this technology, visit the ECT page on the FHWA NDE Web Manual.

"ECT instrument. This photo shows the face of the eddy-current testing instrument. The upper portion of the instrument is a screen displaying a signal image. The bottom portion of the instrument has various controls. One end of a cable is attached to the top of the instrument."
Figure 13. Photograph. Eddy Current Testing (ECT) instrument.

AnchorSteel: 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 13). 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.

"ECA Testing System. This photo shows an eddy current array that is incorporated with encoder wheels. This instrument sits on the connector box. "
Figure 14. Photograph. Eddy Current Array Testing System.

AnchorSteel: 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 14). For more information about this technology, visit the PAUT page on the FHWA NDE Web Manual.

"PAUT Systems. A. Phased array.  This photo a phased-array-ultrasonic instrument and transducer near a beam joint. "

A. Phased Array

"PAUT Systems. B. FMC/TFM system. This photo shows a box that works as a processor unit for 128/128 full matrix capture/total focusing system (128 pulser channels and 128 receiving channels)."

B. FMC/TFM System

Figure 15. Photograph. Portable Phased Array Ultrasonic Systems.

AnchorSteel: 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 15). Shear wave methods (angled beam) are commonly used to inspect welds for flaws (figure 16). 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.

AnchorLoading 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.

AnchorX-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.

AnchorLab-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.

"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 R1100 six 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. 

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

AnchorPortable 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.

"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.

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

Robotic Air-Coupled Acoustic Array

This technology has been developed to eliminate the need for physical contact between the sensors and a structure through the application of contactless acoustic sensors. The FAST-NDE laboratory uses contactless acoustic receivers to develop a noncontact, air-coupled acoustic array to inspect bridge decks. This fully air-coupled system is mounted on a robotic platform for the high-speed inspection of bridge decks (Figure 22).

" A robotic air-coupled acoustic array, which is a large yellow machine on wheels. Photo was taken in a lab."
Figure 22. Photograph. Robotic Air-Coupled Acoustic Array.


Equipment for Asphalt

Density Profiling System

The density profiling system (DPS) measures the density of asphalt pavement, in terms of air-voids contents, using ground penetrating radar. The DPS emits electromagnet wave pulses into the asphalt pavement and receives reflected wave signals. Analyzing the wave signal gives the dielectric constant of the scanned area. Based on the correlation between air-void contents and the dielectric constant of asphalt pavement, the DPS measures the density of scanned asphalt pavement. Figure 23 shows a DPS unit for density measurement.

A Density Profiling System on pavement with trees in the background
Figure 23. Photograph. A Density Profiling System for Density Measurement of Asphalt Pavements.