Roadway and bridge deck inspections with ground penetrating radar

• Online Access: http://hdl.handle.net/2047/D20237863

This work evaluates subsurface conditions of roadways and bridge decksfrom the data collected by an array of ground penetrating radar (GPR) prototype systems in an air-coupled mode at traffic speed. The GPR used in the experimental work is one of the prototype sensing systems by the VOTERS (Versatile Onboard Traffic-Embedded Roaming Sensors) project led by Northeastern University.The objective of the VOTERS project is to provide several prototype sensing systems to perform complementary inspections on roadways and bridge decks rapidly and periodically with no traffic closure. This GPR system is operated at 2 GHz with a typical penetration depth of 60 cm in common road materials. The features include high pulse repetition frequency (1000 Hz), large dynamic range, and compacted profile. The GPR transmits an electromagnetic (EM) wave, and records the amplitude as well as two-way travel time of reflection signals. The reflection signals carry significant amount of surface and subsurface information, such as layer thickness, distresses, buried objects, and rebar location and corrosion. For roadway inspections, the objectivesare to locate layer interfaces, calculate dielectric constant and thickness of the asphalt, identify subsurface objects, and predict potential delamination or prepothole conditions. An automatic software package is developed to identify layer boundaries using cross correlation and Hilbert transform algorithms, and to estimate dielectric constant and thickness of the asphalt layer.Identifications of buried objects and potential delamination can be achieved by searching the abnormal changes of reflection signals. For bridge deck inspections, asphalt layer and reinforced concrete layer can be distinguished.In addition, steel rebar in bridge decks can be detected from air-coupled GPR data collected at traffic speed, and the amplitude of rebar reflection can be extracted to estimate rebar corrosion level since corrosive environment significantly attenuates EM wave. Also, diaphragms or/and pipes below bridge decks can be seen from radar images. The major contributions of this dissertation are: 1) develop a software package to identify asphalt layer properties automatically, providing information about the layer interface, dielectric constant and thickness; 2) detect the buried objects up to 60 cm below ground, and distresses in subsurface from abnormal changes of the reflection signals; 3) develop an unsupervised, accurate and efficient algorithm to detect rebar locations and to extract rebar reflection amplitude from ground-coupled GPR data; 4) estimate the corrosion level of steel rebar in bridge decks using rebar reflection amplitude; 5) distinguish asphalt from reinforce concrete in bridge decks; and 6) demonstrate the possibility to design an algorithm for rebar detection from air-coupled GPR data. The results indicate that the GPR array can provide comprehensive subsurface conditions of roadways and bridge decks in network level.