Infrasense, Inc., a national leader in infrastructure nondestructive evaluations, has recently completed GPR data collection for 116 bridge decks throughout Montana, covering nearly 900,000 square feet. The Infrasense survey crew is currently working to collect infrared thermography data on 119 bridge decks across 4 different regions of Wisconsin. The total deck area for the Wisconsin work amounts to over 1 million square feet, which would have taken months to evaluate using traditional methods such as sounding. But these decks are surveyed in only a few weeks with the Infrasense subsurface scanning system. Following data collection, the NDE data is processed, and subsurface damage is then quantified and mapped using Infrasense’s proprietary software systems. The final delamination/ deterioration quantities and maps allow bridge engineers and managers to both prioritize future repair, rehab, and replacement efforts, as well as scope out the extent of repair for contracts being put out to bid.
Ground penetrating radar (GPR) data is collected at highway speeds, making it the fastest NDT technology to estimate rebar depth, corrosion conditions and deteriorated concrete. The GPR data is collected in a series of lines spaced 3 feet transversely across the width of the deck, with each line representing a cross sectional slice of the deck at a particular offset. Decks in good condition consist of strong and uniform radar reflections from the rebar. GPR data with weak and inconsistent reflections indicate rebar-level deterioration in the bridge deck.
The infrared data is collected in a series of passes across each deck, with each pass covering a deck width of between 12 and 15 feet. Surveys are performed at normal driving speeds to prevent lane closures and traffic disruptions. During the survey, regular visual data is collected synchronously with the infrared data, so that surface features such as staining and patching can be differentiated and mapped in the infrared images.
Ground penetrating radar surveys and infrared data provide transportation agencies with accurate and comprehensive bridge deck condition information, enabling effective preservation, rehabilitation, and replacement decisions. With large bridge deck inventories, highway agencies have primarily relied on visual inspection. Since the mechanisms of deterioration occur below the surface, subsurface investigation is most effective to evaluate the estimated lifetime of these bridges.
Highway agencies have begun to move away from employing sounding (chain or hammer) to identify delaminated areas for project-level rehab. Although sounding has proven reliable, the labor and closures required for a sounding survey makes it prohibitive for obtaining data of a large number of decks. Also, sounding is not effective when there is an asphalt overlay.