Infrasense Carries out Ground Penetrating Radar (GPR) and Infrared Thermography (IR) Condition Surveys of 17 Bridge Decks in Wisconsin’s North Central Region

This past summer, Infrasense conducted a multi-faceted non-destructive survey and report for 17 bridge decks in Wisconsin DOT’s North Central Region.  The project provided the client with a comprehensive set of condition results to facilitate a data-driven approach to programming their bridge inventory. Surveys were performed at normal driving speed with no disruption to traffic.

The GPR data collection system included a pair of 2 GHz horn antennas and a SIR 30 control unit, both manufactured by GSSI in the United States.   The infrared survey was performed using a FLIR camera mounted on top of the survey vehicle along with a visual feed for reference.  The final report included a quantitative table of deterioration, debonding, patching, and spalled areas.  A select number of the decks were chosen by the client for further reporting, where Infrasense provided plan-view maps of their findings, along with ground-truth confirmation at suspect locations on the decks.  Finally, the report included an underside visual inspection summary, with pictures and descriptions. 

 Final map of a bridge deck consisting of GPR, IR and sounding

Final map of a bridge deck consisting of GPR, IR and sounding

The GPR bridge deck surveys are carried out according to ASTM D6087-08. The resulting data shows a cross-sectional slice of the bridge deck at various offsets. Each slice includes the top of the deck, top mat of reinforcing steel, and the bottom of the deck. The amplitude of these layers is calculated and then quantities and maps of concrete deterioration and concrete cover are produced. The resulting maps are provided in both PDF and CADD compatible formats.

The infrared bridge deck surveys are carried out according to ASTM D4788-03 (2013). The infrared data is reviewed simultaneously with the video data to differentiate delaminated areas from surface features (discoloration, oil stains, sand and rust deposits, etc.) that appear in the infrared, but are unrelated to subsurface conditions. Subsurface delaminations produce a thermal barrier and result in higher surface temperatures as the sun heats up a deck. These higher temperature areas are detected with the infrared camera, and subsequently quantified and mapped.