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Non-Destructive Quality Control with GPRGround penetrating radar is an excellent tool for characterizing reinforcing steel within concrete structures.Unlike radiography, GPR doesn't require accessing both sides of the structure, doesn't require distancesetbacks for safety reasons during data collection, and is able to collect data much faster over a large area.Researchers continue to push the limits of GPR to improve resolution and data processing techniques to accuratelymeasure depth and geometry in three dimensions. Instruments also become smaller and smaller as computersalso shrink in size, making GPR very portable and feasible to collect data in difficult to reach locations.GPR consists of an antenna, a control unit, and a computer data recorder and GUI. Data is collected by moving theantenna across the concrete surface. Radar signals from the antenna reflect off of reinforcing steel and return tothe antenna where they are received and recorded. The information can then be processed and displayed either asa cross-sectional depth profile or combined to create a three dimensional block of data that can be viewed in plan.The figure to the bottom right is an example profile of GPR data and the figure below is a horizontal slice through a3D block of data shown in plan view.Schnabel Geophysicists obtained the data below, shown in plan view, for quality control on precast elements toconfirm that reinforcing steel was placed properly and had the specified minimum cover. We can clearly observecenter of the reinforcing bars to measure center to center distance and the depth to the bars.Radar AntennaRadar UnitInterpreted Deeper Reinforcing Steel LocationLEGENDInterpreted Shallower Reinforcing Steel Location2.50"Location and Estimated Depth to Reinforcing Steel in InchesRebarGPR can generally penetrate up to about 4 ft into concrete althoughaccurate steel locating is typically limited to about 18-24 inches.AntennaDirection ofTravelConcreteSlab SurfaceConcreteReinforcingBarGeneralizedAntennaRadiationPatternGPR TraceResultingfrom BarExample GPR Profile ViewExample GPR Plan ViewDocuSign Envelope ID: 3667B243-40E4-479A-AE63-F797402CD54A