Infrasense was recently contracted to perform ground penetrating radar (GPR) and infrared thermography (IR) services on 17 bridge decks in Wisconsin's southwest region. These tests provide condition information for the reinforced concrete decks quickly and without the need for coring.
Infrasense, Inc., a national leader in detecting subsurface conditions, has recently been contracted to perform subsurface investigations for 17 bridge decks in Wisconsin's southwest region. A suite of nondestructive tests will be performed, including a ground penetrating radar survey, infrared thermography scanning, and impact echo testing. These tests provide a condition assessment of the reinforced concrete bridge decks without requiring any cores or exposed rebar, and with minimal disruption to traffic flow.
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) 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.
Ground penetrating radar (GPR) data is collected to estimate rebar depth and corrosion conditions. 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. 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.
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, the maximum amount of information can be obtained for the least cost. Decks with concrete overlays are common in Wisconsin, and illustrate how GPR and IR methods complement each other.
Infrared surveys are effective in detecting overlay debonding, while GPR is effective in detecting rebar-level delamination. Combining GPR and IR methods becomes economical when applied with a two-level survey approach.