Spectra Subsurface Imaging, LLC performed a ground penetrating radar investigation along the surface of the Tahawus Road bridge in Newcomb, New York. The purpose of the investigation was to determine the internal quality of the bridge deck.
For this project, a hand-held ground coupled antenna with a frequency of 1600 MHz was utilized. This high frequency antenna has a penetration depth of about 18 inches and is used to investigate subsurface features that are relatively close to the surface and small in size. This antenna helps to provide information on bridge deck thickness, the presence and pattern of reinforcement, and the identification of potential voids and deterioration areas.
The GPR investigation revealed widespread reflection amplitude loss. Significant amplitude loss has been correlated with increased chloride concentrations and concrete deteriorations. Approximately 40% of the individual rebar reflections had a reduced amplitude below a threshold level that may correspond with deteriorations. Areas of possible fractures/voids were also identified and mapped. A coring program performed subsequent to the GPR investigation confirmed the GPR study results.