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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tensioning and an in-situ deck slab), supported on longitudinally post-tensioned cantilever sections. The support and articulation for the precast main span elements are via half joints at the end of the precast cantilevers. Samples 1 and 2 have been extracted from the end of the cantilever, being two adjacent sections containing half joints and PT ducts. The samples vary in size between 2m to 3m in length and width, weighing 16 and 24 tonnes respectively. Sample 1, being the outermost section, also includes the parapet beam support and a patterned finish to the external-facing elevation. Sample 3 has been removed from the opposite side of the same cantilever monolith, starting at the pier support diaphragm and extending 6m along the cantilever section, being 4m tall at the highest (diaphragm) end. The section has been taken from part of the outermost cell, and as such contains part of the top and bottom flanges of the cell, along with the web. The external façade of the web is patterned and contains a diagonal nib to support the parapet beam (as per Sample 1).

Figure 1 – (Left to right) A14 HRV Samples 1, 2 and 3

3.3. NDT Technologies Deployed and Specification The initial plan included engaging with some of the industries most established NDT suppliers to provide a suite of NDT techniques. This included optical/spectral inspections, electromagnetic sensors, mechanical wave induction and electrochemical tests. Testing providers initially included VSL (also acting at the main works contractors) Bridgology, Mistras, CTS, Allied Associates and the Royal Agricultural University (RAU). Many of the techniques were commonplace; Ground penetrating radar (GPR), covermeter surveys, ultrasonic tomography, half cell potential surveys and impact echo, but a number were also less common; Hyperspectral imagery, FTIR gas monitoring, magnetic flux leakage, chloride mapping via GPR and ultrasonic guided wave testing. Over the course of the project, a number of new technologies and testing providers were brought into the project as they were identified. This included Screening Eagle, bringing the latest Proseq sensors, HausBots, deploying their climbing robot, reinforcement scanning specialists Hilti and Muon tomography specialists GScan. The intention for each form of NDT is that it builds on the overall dataset which will allow structural condition to be appraised. Furthermore, the project team acknowledge that in the majority of cases, the most advantageous use of each form of NDT is best identified by the technology provider. Based on the above requirements, the project specification produced for the NDT was primarily defined by outcomes, rather than prescriptive approaches. A hierarchy of data value was established, identifying the types of defects or data measured and their relative value, ranging from lower value data (e.g. locate the ducts and reinforcement), through to the highest value data (e.g. identify corrosion, section loss or wire breaks). Leveraging this, it was the requirement that the technology providers themselves confirm the deployment methodology to obtain the best possible results. 3.4. NDT Key Outcomes to date At the time of writing, detailed NDT findings are still being collated, however outline results and initial findings as noted within this Section – further information is available and will be presented at the conference. 3.4.1. Half Cell Resistivity Detailed electro-potential readings, dust sampling and chloride content testing carried out immediately prior to demolition (of the samples) are yet to be provided, however initial resistivity testing of the exposed faces results have typically been found to show low likelihood of deterioration in the near surface reinforcement and concrete, with some