The Federal Highway Administration’s (FHWA’s) Advanced Sensing Technology (FAST) NDE Laboratory is a unique facility for the development and testing of NDE technologies. The FAST NDE laboratory works with different offices and programs within FHWA and with other stakeholders to address their growing needs with state-of-the-art NDE tools. Some of the technologies researched at the laboratory include: conventional/phased array ultrasonics; conventional/advanced eddy current; acoustic emission; ground penetrating radar; infrared thermography; impact echo; Structural Health Monitoring (SHM) systems; autonomous tools for condition assessment and automated data collection, analysis, interpretation, visualization and data fusion; and both noncontact and remote sensors.
The laboratory is outfitted with new equipment and tools, such as a KUKA robotic arm (KR 10 R1100 sixx) with a payload of 10 Kg to handle test specimens, multiple NDE equipment, such as a phased array ultrasonic testing system for steel component inspection and ground penetrating radar for concrete inspection (see Equipment page for a complete list).
Figure 1. Image. Artist’s rendition of the FAST NDE Laboratory.
Figure 2. Photograph. The FAST NDE Laboratory.
The FAST NDE Laboratory has an extensive collection of component specimens to support the NDE program. Component specimens include small sections of highway structures (both in pristine conditions and with known defects) that have been removed from in-service bridges or that are manufactured to represent realistic structural components. The collection of component specimens is continually evolving as specimens become available from decommissioned bridges, are purchased from qualified vendors, or are manufactured in the NDE Laboratory. A summary of the specimens currently at the NDE Center is described below.
The lab houses a pair of full-sized (54-inch-tall by 85-foot-long AASHTO girders) prestressed bridge girders that were removed from an active bridge on Maryland I–90. These girders were installed in 1971 and were in service until they were salvaged to be used for full-scale research in a laboratory setting at the Turner-Fairbank Highway Research Center (TFHRC). The girders were placed on four reinforced soil abutments, suspended approximately 10 feet above the ground (figure 3).
Figure 3. Photograph. Full-size prestressed bridge girders.
Three validation slabs, measuring 4 feet long, 6 feet wide, and 8 inches high, are also available to verify the applicable and promising methods used on girders (figure 4). The validation slabs were constructed with prestressing strands laid lengthwise throughout with known amounts of strand damage artificially created at known locations. Each validation slab has 26 untensioned half-inch 7-wire stands arranged in 3 vertical layers and 15 longitudinal rows. Several different scenarios of damage were created in each slab, including 5 percent, 10 percent, 25 percent, and 100 percent section loss at predetermined locations (figure 5).
Figure 4. Photograph. Validation slabs after pouring.
Figure 5. Photograph. Artificially created strand damage.
The specimen library also includes a 6-foot long, 8-foot wide, 9-inch high concrete slab with built-in delaminations at predetermined locations used as a blind testbed for NDE technologies (figure 6). Multiple methods are used to create these delaminations, such as embedded cardboard, sandwich concrete plates, and polyethylene sheets, with the purpose of studying applicability and viability of NDE technologies and tools to detect these built-in defects.
Figure 6. Photograph. Concrete slab with built-in delaminations.
Seven slabs are available to identify effective and promising NDE techniques to assess the performance of concrete bridge deck overlays and detect and characterize deterioration in deck overlays (figure 4). The slabs, with seven types of overlays, measure 10 feet long, 40 inches wide, and 8 inches thick. The slabs were built with various artificial defects including delamination, honeycombing, void, vertical crack, and precorroded rebar within an elevated chloride content environment. Half of each overlay was bonded to the underlying concrete slabs; the other half was debonded.
Figure 7. Photograph. Epoxy, latex (covered by a white sheet), silica fume (covered by a blue sheet), and polyester polymer overlays after construction.
Figure 8. Photograph. Construction of asphalt overlays with liquid membrane, sheet membrane, and without a membrane.
Figure 9. Photograph. Construction of asphalt overlay specimens utilizing a nuclear density gauge to ensure adequate compaction.
To test the anchorage systems of highway barriers in the laboratory setup, a 12-foot long, 8-foot wide, 8-inch high mockup bridge deck along with concrete barriers are available in the laboratory (figures 10 through 13). The barriers selected were attached to the mockup bridge deck using four #4 and four #6 reinforcing steel bars with different levels of simulated cross-section loss (0, 10 percent, 25 percent, and 50 percent), as shown in figure 14 .
Figure 10. Photograph. Mock bridge deck.
Figure 11. Photograph. Retired service barrier.
Figure 12. Photograph. Jersey barrier with delaminations.
Figure 13. Photograph. Barriers with delaminations.
Figure 14. Photograph. Simulated cross-section loss of rebar at F-shape bolt-down barrier connection and New Jersey barrier connection.
Three bridge decks, measuring 30 feet long, 5 feet wide, and 8 inches thick, were salvaged from the replacement of the Haymarket highway bridge in 2015 for full-scale, long-term NDE research in a laboratory setting at TFHRC (figure 15). The Haymarket bridge was built in 1979 with reinforced concrete decks on continuous steel girders. The three salvaged decks were placed on two reinforced soil abutments, suspended approximately 7 feet above the ground at TFHRC. The condition of the decks has been repeatedly evaluated using various NDE techniques including infrared camera, electrical resistivity, impact echo, ultrasonic surface waves, ground penetrating radar, and ultrasonic tomography.
Figure 15. Photograph. Three bridge decks from the Haymarket highway bridge.
This collection includes samples from steel bridges with different configurations. The specimens have different joint geometries, material thicknesses, coatings, and weld defects. The inventory includes a number of butt-weld specimens with Complete Joint Penetration (CJP) groove welds, butt-welds with well-bonded bridge coatings, and T-joint specimens with fillet weld butt joints. Engineered cracks are embedded in these specimens and a variety of crack geometries are represented.
Bare Metal Steel Specimens
Figures 16 through 20 show each of the specimen’s geometries. The specimen base metal complies with ASTM A709 material specifications. All fabrication and welding was performed in accordance with the American Welding Society (AWS) D1.5 Bridge Welding Code.
Figure 16. Photograph. Typical T-Joint specimen with fillet welds.
Figure 17. Photograph. Typical T-Joint specimen with fillet welds.
Figure 18. Photograph. Typical butt joint specimen with CJP groove welds.
Figure 19. Photograph. Typical T-Joint specimen with fillet welds.
Figure 20. Typical heavy thickness specimens with butt welds.
Coated Steel Specimens
The purpose of the coated specimen shown in figure 18 was to evaluate the effect of typical bridge coatings on measurements. The specimen was coated with a typical three-coat bridge system. The three-coat bridge system comprises of an organic zinc-rich primer, an epoxy intermediate, and polyurethane topcoat applied by KTA-Tator. This coating was a mixture of KTA-Tator’s Carbozinc® 859; Carboguard® 893SG with optional (LT) cure, and Carbothane 133 LH products. This coating system is a well-established and commonly used system by departments of transportation in the United States.
Figure 21. Photograph. Typical coated specimen.