PSI - Issue 64
Chris Mundell et al. / Procedia Structural Integrity 64 (2024) 191–198 Author name / Structural Integrity Procedia 00 (2019) 000–000
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3.4.9. Field Spectroradiometry and Hyperspectral Imaging Using field and laboratory spectroradiomters (ranging in the 280 to 2500nm spectra) in addition to a Raman spectroscopy device using an active light source (a monochromatic laser), further measurements of chemical composition can be remotely undertaken. Additional spectral analyses was carried out using a Specim IQ camera, recording in the 400 to 1000nm range. Although full data processing has not yet been concluded, to date there have been no significant or noteworthy findings from the data obtained via these methods. 3.4.10. GPR Chloride Mapping Using GPR data, Bridgology are able to develop a ‘heat map’ of chlorides and corrosion risk in a surface. In this case, the technology has used the Proseq GP8000 GPR scan, undertaken in scans 100mm apart and along two perpendicular directions (i.e. forming a grid of data). The technique has found some indicators of elevated risk of corrosion, particularly focused around the re-entrant corner of the half joints. This is of particular interest, and is not unexpected due to the known cracking along this location and historical deterioration of the structure. 3.4.11. Magnetic Flux Leakage (MFL) German-based company IFDB were engaged to deploy MFL testing, which involves remotely magnetizing the tendon from the sample surface and then measuring the magnetic flux density along the tendon path using magnetic sensors. Due to the specifics around the magnetization and interference/reflection from cut ends, the MFL technology is most suited to large, planar surfaces or long lengths of beams. As such, there were limited areas of applicability for MFL within the A14 samples. However, it was successfully used on Sample 3, both on the top surface and the exposed web. The team were successfully able to obtain signals from 5 of the 7 ducts within Sample 3, however there was no clear evidence from this technology of wire breaks within the strands. 3.4.12. Muon Tomography The final technique tested uses an emerging technology called Muon Tomography. Muons are subatomic particles – similar to electrons - that are formed when cosmic radiation hits the earth’s atmosphere. Muons are harmless to life, and have very high levels of penetration, which make them ideal for inspecting through dense structures such as a bridge elements. There are a number of methods for tracking the passage of the muons, however the method deployed by specialists GScan for the Moonshot project use high-technology materials such as Plastic Scintillating Fibers and Silicon Photo-multipliers, allowing the path of individual muons to be measured. By measuring over a long period of time (several weeks), the deviations of the muons due to changes in medium (e.g. where they pass from concrete into a metallic duct) can be detected, allowing an image or model of the area in front of the scanning plates. The technology promises to provide not just an image/model showing the various key elements (e.g. duct, tendons, reinforcement), but also the chemical composition of the materials, potentially showing deterioration and the presence of rust. The key limitation for this technology at present is the infrequent nature of the passage of muons; In order to build up a picture that shows defects at the scale required (i.e. millimeter precision), the scanning devices need several weeks left in situ, with the area under observation therefore limited to the size of the scanning plates. In addition, a continuous power supply – although not large – is currently required for the system, which may add logistical complexity for in situ bridges. For the purposes of the Moonshot trials, two number sensors were used, one above and one below the concrete flange of Sample 3, and left for a total length of five weeks. The arrangement was locally moved after 2 weeks, with the intention of the second position enabling a 3D image. At the time of publication, the images and data obtained are still under development, with further trials under discussion. 3.5. Hydrodemolition This aspect of the project has now moved into the final phase of work, being the controlled demolition of the
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