Phenomenology Study of HERMES Ground Penetrating Radar Technology for Detection and Identification of Common Bridge Deck Features

Foreward This report documents the findings of a phenomenology study that analyzes the performance of HERMES ground-penetrating radar technology. HERMES technology was designed for the evaluation of concrete bridge deck deterioration, with a particular emphasis on the detection of corrosion-induced delaminations. HERMES technology was developed by Lawrence Livermore National Laboratory through a cooperative research agreement with the Federal Highway Administration (FHWA). Research funds for the project were provided by the FHWA and recently a State pooled fund has been established to continue funding system improvements. This report will be of interest to bridge engineers, designers, and inspectors who are involved with the evaluation of our Nation's highway bridges. Notice This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Government assumes no liability for its contents or use thereof. This report does not constitute a standard, specification, or regulation. The United States Government does not endorse products or manufacturers. Trade and manufacturers' names appear in this report only because they are considered essential to the object of the document. Accurately evaluating the condition of a bridge deck over time and using this information to choose appropriate maintenance techniques has become critical for the efficient allocation of resources to bridge deck maintenance. Tomographic imaging of subsurface bridge deck features using ground penetrating radar (GPR) is one method of addressing this problem that has been pursued through a research program at the Federal Highway Administration (FHWA) Nondestructive Evaluation Validation Center. Prototype GPR systems, developed by Lawrence Livermore National Laboratory (LLNL), have been used in a phenomenology study of several controlled specimens. These specimens were designed with subsurface features that simulate cracks, voids and other common problem phenomena for bridge decks. The specimens have some unique features that make the data collected from them compelling. Results from these phenomenology tests are the primary focus of this paper. Field tests have also been conducted that produced inconsistent results, clarifying the need for system improvements. These improvements are planned for incorporation into a new prototype GPR system currently beineloped by LLNL that will be tested by FHWA in the coming year.