FHWA NDE CENTER RESEARCH & DEVELOPMENT
The PERES Bridge Inspector
The PERES bridge inspector consists of a single transceiver mounted on a computer controlled robotic cart. An illustration of PERES is shown in Figure 1. The transceiver is moved across the surface of the road along a rail which is fixed perpendicular to the direction of cart movement. As the transceiver is moved along the rail, data is
collected at regular intervals. Subsequently, the whole cart moves forward a specified amount. The process is repeated until the required area of the bridge deck has been surveyed.
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| Figure 1.The PERES bridge deck inspection system. |
Because the survey speed of PERES is relatively slow and there is only a single antenna pair, there is sufficient time to collect numerous samples at each location over the road surface. Approximately 100 samples are collected and averaged at each interval in time, reducing random noise. Therefore, the data from PERES is of higher quality and has a higher effective signal to noise ratio than HERMES.
The sampling interval along the rail may be varied and the distance PERES moves between sweeps of the transceiver can also be adjusted. A spacing between measurements of 1 cm is possible in both forward and transverse scan directions when high horizontal resolution is required. Moving the transceiver at such small intervals with the precision granted by the robotics provides extremely versatile data. Data taken over a well-defined grid facilitates synthetic aperture processing techniques such as wavefield backpropagation. Images can be produced that represent many features of the bridge deck's internal structure in a realistic rendering.
Images obtained over a concrete reinforced bridge deck, after processing using diffraction tomography, are displayed below in Figures 2 and 3. This data was collected July 14-16, 1998 at the Floriston Bridge, which is approximately 10 miles east of Truckee, California.
1.5 m |
| 7.3 m Figure 2. Reconstructed PERES data showing a horizontal plane through a reinforced concrete deck. |
These images indicate the presence of reinforcement, location of a bridge joint and some anomalous areas which were speculated to be voids. Cores of the anomalous zones found that there were indeed voids in the concrete at these locations. Additionally cores in areas which did not show anomalous reflections did not locate voiding.
0.2 m |
| 7.3 m Figure 3. Vertical cross-section reconstruction of PERES data. |
Phenomenology testing has also been conducted on specimens designed and fabricated at the FHWA NDE Center. This testing has made quantitative assessments of system performance possible. Figure 4 presents data collected from one of the phenomenology specimens, designed to quantify PERES depth resolution. This reconstructed data set indicates high magnitude radar reflections in white while lower magnitude radar reflections are indicated by
shades of gray down to black for the lowest magnitude. The white feature in the middle left of the image indicates the response to a 2.54 cm thick foam insert, while the feature in the lower middle of the image indicates a 0.64 cm thick foam insert. Two very thin polyethylene
sheets (0.1 and 0.2 mm thick respectively) in the specimen were not detected. Reinforcing steel in the specimen is indicated by light colored, linear features in the image that traverse it horizontally
and vertically. Continuing phenomenology testing of both PERES and HERMES will aid future HERMES II development significantly.
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| Figure 4. Reconstructed PERES data from a FHWA NDE Center phenomenology specimen. |
For More Information, please contact either by e-mail or telephone:
Dr. Mike Scott (202) 493-3124
Dr. Ali Rezaizadeh (202) 493-3119
Advanced Ground-Penetrating Radar Inspection of Bridge Decks
The Problem of Deteriorating Bridge Decks
The HERMES Bridge Inspector
Current Work on Hermes II
