Defective grouting in Post tensioned Structures

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The gamma-ray tomography technique developed by THASA is also a valuable tool for the study of the condition of grouting in PT girders and of corrosion in the strands.




Below we show an example of such a successful study performed at one of the largest bridges in Argentina (Work contracted by COWI International).



The images correspond to a large girder in the Zárate Brazo Largo Bridge complex in Entre Ríos, Argentina. They show a case of severe grouting defect (dark band in the left hand side image) in the upper duct, compared with another sector which shows no defects.


A detailed description and analysis of the results of this work can be found here.

Results of a similar work performed in Portugal can be found in here.


THATIR technique applied to the study of “deep” post tensioned ducts

A request from Simpson, Heger and Gumpertz of Waltham, Massachusetts (SGH) prompted THASA to develop an adaptation of the THATIR technique (+ info) for the study of grouting defects in “deep” ducts (i.e., ducts embedded in the interior of large concrete structures) where the gammagraphic method is not applicable. This new version of THATIR entails displacing source and detector along small holes drilled at each side of the duct. The technique was successfully tested on 6 samples prepared by SGH.  The results show that locations of the boundaries between grouts of different densities can be determined with a  1 mm  precision and the densities themselves to better than 10%.


Cross section of one of the samples prepared by Simpson, Gumpertz & Heger.

1. rebar; 2. duct top edge; 3. air void; 4.soft grout; 5. solid grout; 6.strand; 7. duct bottom edge








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