Development of Tendon Imaging Sensor
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2019-08-01
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Edition:Final Report 01/01/2016 - 08/30/2019
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Abstract:Inadequate grouting is associated with corrosion of post-tensioning steel in grouted tendons used in construction applications. This project was conducted to develop a nondestructive method capable of economical, rapid imaging assessment of grout deficiencies of external tendons in the FDOT structural inventory. The method uses electrical impedance measurements by means of a traveling sensor placed on the outer surface of the tendon duct, combined with a magnetic detection method that determines the envelope of the strand bundle in the cross-section of the tendon. Integration of strand position and impedance information was processed to produce a color-coded image of the tendon cross-section that distinctly flags the presence of a full void and provides immediate visual differentiation between sound and deficient grout locations. Other void configurations and regions of unhydrated grout produced a signature pattern intermediate between that of full voids and sound grout. Regions with a higher water content resulted in lower impedance values than those observed with sound grout. Those cases were flagged with proper independent calibration. Tests for validation of the method against gamma ray tomography scans confirmed the ability of the method to reveal the presence of full voids in an image that includes strand position information.
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