Infrasense Returns to the Leo Frigo Bridge in Green Bay to Perform Impact Echo Testing

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Before the reopening of the Leo Frigo bridge in early January, Infrasense responded to WisDOT's request for impact echo testing of the repaired section of the bridge between piers 21 and 23 to detect potential areas of asphalt debonding or concrete delamination. Infrasense previously performed ground penetrating radar (GPR) scanning on the sagging portion of the bridge in November 2013.

Infrasense engineer inspecting the surface of the sagging portion of the Leo Frigo bridge in November 2013

The Leo Frigo Bridge, an 8,000-foot long bridge over the Fox River in Green Bay, Wisconsin that typically carries around 40,000 motorists each day, reopened to the public on January 5, 2014 after a nearly 3-month closure. In late September, pier 22 sank approximately two feet due to corrosion of its pilings and caused a significant sag in the structure. The Leo Frigo bridge, which carries Interstate 43, had been closed to traffic since September 25. Repair plans, which included installing new pilings to piers 21 through 25 and jacking the deck back into place at pier 22, allowed the bridge to reopen in January 5, 2014. Engineers at the Wisconsin Department of Transportation (WisDOT) used the bridge closure to thoroughly investigate the condition of the concrete bridge deck and asphalt overlay.

Days before the bridge reopening, WisDOT called in Infrasense, Inc., a national leader in detecting subsurface conditions, to perform Impact Echo testing on the asphalt driving surface of the deck to detect any areas where the asphalt may have debonded from the concrete bridge deck. Despite the bitter cold temperature, Infrasense was able to complete its testing and even give a demonstration to Governor Scott Walker, who was on site to view the repair progress ahead of the planned reopening.

The impact-echo test generates a sound wave via an impact with the test surface, and measures the wave response to provide a resonant frequency associated with the deck slab thickness. If the slab is intact, the thickness data is clear, and should correspond with the expected slab thickness. If the slab is delaminated, the thickness data is unclear and does not correspond to the thickness of the slab. Typically, impact-echo testing cannot be used effectively on asphalt surfaces because the impact is absorbed by the relatively softer bituminous material. However, in cold weather, asphalt becomes very stiff and sound waves will travel through the material with ease. Thanks to the record-breaking cold that hit the entire Midwest in early Janurary, Infrasense was able to effectively perform impact echo testing on the Leo Frigo bridge deck to locate potential areas of debonding.

In November 2013, Infrasense performed vehicle-based Ground Penetrating Radar (GPR) testing across the entire width of the Leo Frigo bridge from pier 21 to 23 in order to investigate the subsurface condition of the sagging portion of the bridge deck. Infrasense responded on short notice to carry out the work in early November, and was among the first vehicles to drive onto the sagging portion of the bridge after the temporary bracing was installed.

GPR and Impact Echo were just two of the methods being used to evaluate the structure and ensure it was safe to reopen to the public. In this regard, Infrasense was able to meet a tight project schedule and provide the deck condition results to WisDOT within the strict time constraints.

Ground penetrating radar (GPR) data is collected to estimate rebar depth and corrosion conditions. GPR condition information is used by agencies at a management level, to distinguish, categorically, that level of action required to preserve a group of decks. That is, for example, which decks require minor repairs, patching, an overlay, or replacement. Additionally, once these higher-level decisions are made, GPR can be used as a scoping tool to determine the extent of repair required for a particular deck.

About Infrasense, Inc.

Since 1987, Infrasense, Inc. has applied the most current technologies to the most difficult challenges in subsurface scanning. Infrasense’s engineers are able to nondestructively extract critical information from a diverse range of structures. The firm has conducted research to advance the field of subsurface detection, while also providing valuable information to clients across the country. Learn more about Infrasense, Inc. and its services at

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Sarah Kelly
Infrasense, Inc.
+1 (781) 648-0440
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