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Determination of Grouting Defects in “Deep” PT Ducts Using Gamma Rays

Grouting defects in PT ducts have been observed in the past by recording the trasmitted gamma-ray intensity on film or digital plates. However this method is limited to structures no thicker than 2 ft. To overcome this limitation a system has been developed in which a source and a small gamma-ray spectrometer are displaced along two holes drilled at each side of the duct to be investigated. This methodology was tested in 6 samples with various defects provided by Simpson, Gumpertz and Heger from Massachussets. Layers of different grout heights and densities were determined in most cases with accuracies better than 0.1" and 0.1 gcm3, respectively.

1. Mariscotti M.A.J., Jalinoos F., Frigerio T., Ruffolo M. and Thieberger P., “Gamma-Ray Imaging for Void and Corrosion Assessment”, ACI International, November 2009, Vol. 31 No. 11 pp. 48-53. 2. Pimentel M., Figueiras J., Mariscotti M.A.J., Thieberger P., Ruffolo M., Frigerio T., “Gamma-ray inspection of post tensioning cables in a concrete bridge”, Structural Faults & Repair 2010, Edinburgh, United Kingdom, June 15 to 20, 2010. 3. THATIR was originally developed for the non-destructive determination of calcium deposits in underground pipes of the city water network. Argentine Patent AR-018132-B1, 2004.
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