Ground Penetrating Radar— Deciphering the Signals

Ground penetrating radar (GPR) continues to gain use as a non-destructive investigative tool for existing reinforced concrete structures. Structural engineers conducting a flexural strength evaluation as part of a condition appraisal can use GPR to identify the relative positioning of reinforcement within the concrete element for use in their calculations. Different techniques can be used to convert the recorded time signals from the GPR into depth measurements. These techniques could include implementing an equipment-based default for the dielectric constant for the surveyed concrete, selecting a user-defined dielectric constant for the surveyed concrete, or creating a site-specific calibration using depth measurements recorded at destructive exploratory openings. Ultimately the usefulness of the GPR information to the structural engineer is a function of the accuracy of the technique used to convert the recorded time signal to an estimated depth. This paper presents a case study on the implementation of several conversion techniques, and compares how these techniques affect the estimated depths to reinforcement to be used in the strength calculations.