PSI - Issue 64

Chris Mundell et al. / Procedia Structural Integrity 64 (2024) 191–198 Chris Mundell / Structural Integrity Procedia 00 (2019) 000–000

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areas of hotspots, such as the re-entrant corners of the half joints of Samples 1 and 2. 3.4.2. Ultrasonic Pulse Echo

Ultrasonic Pulse Echo testing has been independently undertaken by a number of NDT providers, including Mistras, Screening Eagle and Allied Associates. Focus of testing has been on Sample 3 where the suspected wire breaks are located. This testing has identified a number of suspected voids within the tendon ducts, particularly within the web of the sample. This would indicate that at several points along the length of the tendons there is a lack of grout within the ducts, which would in turn provide an elevated risk of tendon deterioration. 3.4.3. Impact Echo Similar to the ultrasonic tomography, impact echo testing has focused on Sample 3 for the most part, and has again found a number of areas where there are strong indications that there is voiding within the sample and the ducts at a number of locations. 3.4.4. Ultrasonic Testing of Wires Using a probe mounted to the exposed ends of the strands, a signal is induced to the individual wires within the tendons, with Mistras proprietary software analysing the signal for approximately 1m along the length of the tendon. The system has identified a number of tendons where there is a strong indication of corrosion along the length tested, although this test is limited to those locations where the tendon end can be cleanly accessed. 3.4.5. Acoustic Emission Testing AEM is normally a passive system that is installed to measure potential tendon breaks over time; for the purposes of these NDT tests, a number of sensors were installed along the length of the samples, with signals induced by a 13cm spring loaded centre punch and a Schmidt hammer. The system measures signal attenuation and amplitude along the length of the sample, looking for breaks and potential indicators for wire breaks. 3.4.6. Ground Penetrating Radar (GPR) GPR has been undertaken using a number of different devices and by a number of different providers, producing detailed coverage of all samples. Although a relatively simple and quick test to undertake, the latest GPR systems have proved effective at locating reinforcement and PT ducts, with multiple scans unlocking 3D images. This technology has been effectively paired with the ultrasonic pulse echo technology, with both complementing the other in detecting voids and moisture. Following the workshop noted above, further tests were commissioned to attempt to use GPR to specifically identify duct deterioration; results from these tests are pending. 3.4.7. Portable X-Ray Flourescence (pXRF) pXRF is a technique used to identifying elemental composition within a sample, and can be applied via a hand held device directly to a surface. The technique can detect many different impurities in the materials (e.g. sulfur, silicon or zinc), but the team focused on identifying corrosion accelerants such as chlorides, which were found to be most abundant in the duct areas. High concentrations of Sulphur were also identified specifically in the duct areas, which is also currently being reviewed further. 3.4.8. Fourier Transform Infra-Red (FTIR) Spectroscopy FTIR Spectroscopy is a gas-sampling approach which uses a Gasmet device through two different applications; either a chamber attached to the surface of the samples, which is sealed and made a vacuum (or as close as possible), or via a ‘sniffer’ which can be inserted into bore holes and cracks. The device then analyses the gases to identify specific variances in gases that are being emitted directly by the sample (compared against baseline readings). In the case of the moonshot tests, over a 10 minute timeframe, there were increases in Methane, Carbon Monoxide and Carbon Dioxide. Methane in particular was measured consistently across all of the samples at the time of the testing, potentially indicating some aspect of biological action. This is being further explored, including repeat testing and consideration of additional testing such as DNA testing of samples following demolition and sample extraction.