Ground penetrating radar as a monitoring tool: Mapping internal features with attribute analysis

In reinforced concrete structures, including those instrumented with embedded sensor networks, severe structural problems often begin as minor issues or maintenance oversights. Unusual behaviors like corrosion or cracking can be detected with embedded sensors as deviation from a reference state of the structure, but verifying the actual cause of the deviation, i.e. localization and characterization, is often limited to targeted nondestructive investigations. Ground penetrating radar (GPR), for example, has been used to investigate defects in structures and can be a powerful tool to compare the physically constructed details of the structure to construction documents. In this work, a post-tensioned concrete pedestrian bridge instrumented with embedded fiber optic sensors was investigated (1) to locate and map continuous internal features of the bridge deck and (2) quantify the differences between the concrete used in each of two construction phases. To this end, a survey of the main span and one of four approaches of Streicker Bridge was conducted using a 2.6 GHz GPR antenna. Analysis of the data using standard processing and filtering techniques was complemented by attribute analysis for improved mapping of features, focusing on the post-tension tendons, embedded air voids, and connections between elements. These results indicate the value of combining nondestructive investigation with SHM sensing approaches for verification of anomalies and understanding of the as-built condition of a structure, as well as providing details for continued SHM of the structure.