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Simulating the Attenuation of Field Collected GPR Signals of Various Reinforced Concrete Bridge Decks

Previous research has shown significant correlations between electromagnetic signals (ground penetrating radar) and active corrosion (half-cell potential) measurements of steel rebar in reinforced concrete bridge decks. However, most of these relationships have been developed using laboratory or field collected data. This research seeks to validate these results using concrete powder samples collected from healthy and corroded bridge decks, and a modeling program designed to simulate electromagnetic waves and their interaction with a modeled bridge deck. The concrete powder was extracted from the decks at three different depths (1in, 2in and 3in) for each core location, and the chloride content of each sample was determined using Quantab ® Titrator Strips. These chloride contents were combined with moisture contents found in the literature to compute the complex permittivity of each location and depth through the Complex Refractive Index Model. These permittivities were then placed into a computer rendered bridge deck model with similar dimensions to actual bridge decks. The propagation of electromagnetic waves through and along the reinforced bridge deck was simulated similar to the field data collection methods. The rebar reflection amplitudes of the actual field radar data were extracted and averaged from signals collected in the same area as the concrete powder samples. The averaged field collected radar amplitudes were plotted against the amplitude of the simulated signals for corresponding locations, and a correlation coefficient of over 90% was computed. This substantiates the idea that electromagnetic signals are correlated with active rebar corrosion and that this relationship can be properly simulated using electromagnetic theory and computer models.

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