Infrasense Performs Nondestructive Evaluations of Tunnels and Bridges in Virginia, Pennsylvania, and Wisconsin

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Infrasense is currently conducting tunnel and bridge subsurface investigations in Virginia, Pennsylvania, and Wisconsin, using a suite on nondestructive testing methods. Infrasense engineers have scanned these structures using ground penetrating radar (GPR) and infrared thermography (IR) to detect delaminations and subsurface deterioration.

Infrasense's vehicle-based GPR system

Infrasense, Inc., a national leader in detecting subsurface conditions, recently is currently conducting condition investigations of tunnel floor slabs in Virginia and bridge decks in Wisconsin and Pennsylvania using advanced nondestructive scanning methods. In Wisconsin, each bridge deck investigation performed by Infrasense consists of a ground penetrating radar survey, infrared thermography evaluation, and impact echo testing. These tests provided a condition assessment of the reinforced concrete bridge decks without requiring any cores or exposed rebar, and with minimal disruption to traffic flow. In Pennsylvania, Infrasense engineers focused on infrared thermography to locate and map near-surface delaminations in the bridge decks. In Virginia, Infrasense used ground penetrating radar to survey and analyze the floor slabs of two tunnels using the bridge deck investigation methodology. The objective of the project is to determine quantities and areas of unsound concrete slab below the asphalt roadway.

Ground Penetrating Radar (GPR) data is collected to estimate rebar depth and identify corrosion. 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 bridge deck deterioration.

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. For a typical interstate deck with 2 lanes and left and right shoulders, the survey is carried out in four passes – one in each lane and one in each shoulder. The survey produces a series of infrared images collected every foot of vehicle travel. During the survey, selected areas that appear delaminated in the IR image are manually sounded to confirm the presence of delamination. Because many of these decks have overlays, the reinforcing can be 4-5 inches from the surface, and sounding is not always capable of detecting delamination at this depth. For those locations where the delamination cannot be confirmed by sounding, testing is carried out using the Impact-Echo method. By analyzing wave frequencies through the concrete, the impact-echo equipment is capable of detecting delamination at any depth throughout the thickness of the deck.

Since 2007, Infrasense has surveyed more than 300 bridge decks across Wisconsin using its multi-phase approach. After completing a quick and simple preliminary (Level 1) bridge deck analysis, many are found to be in good condition and require no further analysis. Those found to have more significant deterioration levels are mapped in detail (Level 2), providing data to accurately plan, program, and budget maintenance and rehabilitation.

Many agencies apply GPR and IR separately as tools for bridge deck assessment, or use only one preferred method. Each method has specific strengths and weaknesses, and Infrasense uses a combination of both to create a more effective bridge deck condition assessment. By combining IR and GPR surveys and using a two level analysis approach, the maximum amount of information can be obtained for the least cost.

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 http://www.infrasense.com.

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Ken Maser
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