Impact Echo is another NDE testing technique that Infrasense uses to assess Wisconsin bridge deck condition. In 2014, Infrasense used this testing method in a unique way on 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 on Interstate 43 each day. In Septemebr 2013, one of the support piers sank approximately two feet due to corrosion of its pilings and caused a significant sag in the structure. The bridge was completely closed to traffic during pier repairs, and 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 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. 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 at the time, Infrasense was able to effectively perform impact echo testing on the Leo Frigo bridge deck to locate potential areas of debonding in the spans effected by the sunken pier.