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FHWA NDE CENTER RESEARCH & DEVELOPMENT
More Information Phenomenology Study of HERMES Ground Penetrating Radar Technology for Detection and Identification of Common Bridge Deck Features
FHWA-RD-01-090, June 2001The HERMES II Bridge Inspector Project
Severe problems with deteriorating concrete bridge decks throughout the United States have prompted the Federal Highway Administration (FHWA) to sponsor a State Pooled Funds Study for a bridge inspection system known as HERMES II, (High Speed Electromagnetic Roadway Measurement and Evaluation System). This system is planned as a second generation-prototype built by Lawrence Livermore National Laboratory (LLNL) with the primary goal of detecting corrosion-induced delaminations in bridge decks. The new HERMES II ground penetrating radar (GPR) technology will be developed using a single transmitter and receiver antenna pair configuration during phase I of the project, which is expected to take one year to complete. This second-generation HERMES II prototype will be built on the knowledge base of experience gained through the design, construction and validation testing of the original HERMES and its counterpart prototype system known as PERES (Precision Electromagnetic Roadway Evaluation System). The original HERMES is comprised of an array of 64 transmitting and receiving antenna pairs while the original PERES uses a single antenna pair. Both of these systems are capable of collecting synthetic aperture radar (SAR) data that can be reconstructed to provide images that are representative of interior bridge deck features. These data reconstructions, which can be presented in three dimensions, have a great potential to improve the quality of bridge inspection practices.
Currently, data from HERMES and PERES do not provide the necessary range resolution to definitively image typical delamination cracks, but field testing has shown that reinforcing steel and bridge deck details are typically rendered in images from both systems. Recommendations for design changes have been made by the FHWA Nondestructive Evaluation (NDE) Center, based on observed response characteristics from HERMES and PERES field testing, to improve system imaging of delaminations. Now that more than 20 states from across the country have reviewed these recommendations through a planning meeting held at Turner Fairbank Highway Research Center (TFHRC), these design changes are being incorporated into HERMES II. A controlled phenomenology study is currently being planned for the new HERMES II that will be conducted by FHWA through its FHWA NDE Center. This phenomenology study will quantify the performance of the system over bridge deck features of interest before it is tested in the field. One phenomenology specimen that was cast for the project is pictured before and after casting in Figures 1a and 1b.
Figure 1a:
Specimen
before casting
Figure 1b:
Specimen
after castingField bridge decks in Northern Virginia and elsewhere are also being scrutinized for their use in HERMES II validation testing.
Another important activity that is being undertaken at the FHWA NDE Center in conjunction with the HERMES II project involves testing commercially available GPR systems. Tests of selected commercial GPR systems will provide an excellent baseline against which the new HERMES II can be critically measured. A test at Van Buren Road Bridge in Northern Virginia, involving one of these GPR systems, is shown in Figure 2.
Figure 2:
A GPR System in use for bridge testingThis is a very exciting time for the HERMES II project and the FHWA NDE Center staff looks forward to the challenge of carefully and objectively evaluating the system LLNL delivers during phase I of the project. The technology in this area has a great deal of potential and studies like this one allow it to be explored for the real world benefits it may provide.
For More Information, please contact either by e-mail or telephone:
Frank Jalinoos (202) 493-3082
Preceding Work on the Hermes Bridge Inspector
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