Infrasense, Inc. recently completed ground penetrating radar (GPR) and infrared thermography (IR) surveys of 7 bridge decks in Maine. The data was collected at driving speed, so that there was no disruption to traffic flow. The GPR and infrared thermography surveys resulted in concrete deterioration and rebar depth quantities and maps.
Infrasense, Inc., a national leader in infrastructure nondestructive evaluations, recently completed ground penetrating radar (GPR), infrared thermography (IR), and high resolution video surveys to evaluate the condition of 7 bridge decks in on the Maine Turnpike. These bridges represent nearly 46,975 square feet along I-95, and all had an asphalt overlay that severely limits the effectiveness of traditional sounding techniques. The GPR surveys were carried out at driving speeds, so no closures were required and traffic flow was not disrupted.
The GPR and IR surveys provide a deterioration quantity and map for each reinforced concrete bridge. The GPR surveys also produced rebar depth and asphalt thickness contour maps for each bridge deck. HNTB will utilize the deck condition results to plan future rehabilitation work on the Maine Turnpike.
Ground penetrating radar (GPR) data is collected at highway speeds 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. Infrasense uses software to analyze and map this data to provide comprehensive results for its clients.
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 and infrared data provide surveys provide transportation agencies with accurate and comprehensive bridge deck condition information, enabling effective preservation, rehabilitation, and replacement decisions. Traditionally, highway agencies have employed 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. In response to these limitations, a number of highway agencies and private consulting firms, including HNTB, have utilized alternative methods such as ground penetrating radar.