For accurate and complete bridge deck condition information, ground penetrating radar surveys enable effective preservation, rehabilitation, and replacement decisions.

For large bridge deck inventories, highway agencies have typically relied on visual inspection at the network level. And since the mechanisms of deterioration occur below the surface, their manifestations are not readily seen in the visual inspections. Consequently, visual deck assessments are often inaccurate, and do not provide a sound basis for planning repair and rehabilitation.

The good news is companies like Infrasense Inc.,, Woburn, Mass., are at work. Infrasense recently carried out deterioration mapping for 12 bridge decks, representing more than 250,000 sq.ft., at the interchange of I-84 and Sisson Avenue in Hartford, Conn.

This mapping was performed using vehicle-mounted high-speed GPR (ground penetrating radar) to scan each bridge deck without requiring lane closures and with no disruption to traffic flow. The GPR data was used to produce deterioration maps and direct subsequent confirmative coring and chloride sampling efforts. The GPR scanning, and coring and chloride sampling provided a comprehensive condition assessment of each bridge deck, including deterioration quantities, which will be used to plan future rehabilitation efforts.

GPR data is collected at highway speeds to estimate rebar depth, corrosion conditions, and deteriorated concrete. This GPR data is collected in a series of lines spaced three 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. Infrasense uses its own proprietary software to analyze and map this data to provide comprehensive results for its clients.

A 2012 study carried out by an independent consultant for MnDOT (Minnesota DOT) evaluated the accuracy of Infrasense’s GPR results. The study compared the predicted quantities for 12 decks surveyed by Infrasense against subsequent construction repair quantities. The study found that, on average, Infrasense’s predicted deterioration quantities were within 3.5 % of the documented construction quantities.

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