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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1. Introduction 1.1. Challenge and Moonshot Vision

Within the transport infrastructure sector, all asset owners face an ongoing challenge to both inspect, maintain and operate their asset stock, whilst maintaining the highest levels of customer service possible. These two drivers are interlinked; to provide a reliable level of service, the assets need to be well maintained and well-managed. However, this is becoming increasingly difficult; key UK bridge owner National Highways estimated that by the end of the decade, 57% of their bridge stock will be over 50 years old. This is coupled with increasing levels of traffic in terms of magnitude and vehicle weights, meaning our structures are under more stress but are also more difficult to inspect and repair due to the disruption associated with road and lane closures. Whether a closure to inspect, maintain or repair a structure is planned or unplanned, the public and political impact can be substantial. To face this challenge, National Highways have instigated a research programme they are calling their Structures ‘Moonshot’. The underlying ambition of this is to maximise the benefits from advances in technology (e.g. new technologies, Artificial Intelligence and Machine Learning) to facilitate new and improved asset management approaches. The ultimate goal is to better understand the condition of our structures and facilitate interventions before deterioration has progressed to the point where major works are required. In the first phase of this project, the team are investigating new approaches associated with internal post tensioning and half joints, of which there are approximately 1200 and 420 respectively within National Highways’ jurisdiction in the UK (AtkinsRealis, 2023). 1.2. Specific Challenges and Approaches for Post Tensioned Bridges Both post-tensioned bridges and those with half joints provide a challenge for asset maintainers to inspect, assess and maintain. For post-tensioned bridges, this is primarily due to the primary load-bearing element typically being located within grouted ducts within the concrete volume and therefore inaccessible to most forms of inspection. For half joints, whilst the external façade of the joint can usually be inspected, the condition of the critical reinforcement along the joint length is often equally difficult to inspect without intrusive and damaging inspection. The issue of inaccessibility is exacerbated when coupled with poor workmanship, poor detailing for water management or inferior construction techniques and materials. This can leave the tendons or half joints exposed to deterioration even in more recently-constructed structures. Whilst the failure of a half joint is usually a more ductile failure mode, failure of individual post tensioning strands can be progressive without any external warning signs and, in the worst case scenario, lead to brittle and catastrophic collapse of structures. Defects may be present from construction, including voids and bleed water in the ducts, bleed water accumulating during grout curing, galvanic reactions from soft grout surrounding hard grout (Fisk & Armitage, 2019), Incorrect placement of ducting leading to low cover, or poor detailing of bridge joints, waterproofing or anchorage cappings 1.3. Post Tensioned Bridge Moonshot - Scope The first phase of the post-tensioned Structures Moonshot was commissioned to articulate the challenge noted above and investigate the approaches that might be developed to meet these objectives. This was undertaken through a ‘Call for Ideas’ challenge statement, which was issued to a broad range of potential research partners. This included engineering and NDT bodies and institutions, but also sought to reach out to potentially compatible institutions and companies within aeronautical, biomedical, agricultural, heavy civils (e.g. nuclear) and mining sectors. Submissions were assessed and scored using a weighted scoring mechanism that considered TRL, evidence of experience in the relevant field, application of the technology, cost and duration to develop, cost to deploy at scale and ease of applicability at scale. As will be described below, the successful proposals for development of next-generation technologies came from Omnia and Sentec. Coupled with the development of these low TRL technologies, the project is also undertaking blind trials on high TRL NDT techniques on large sections of bridge recovered from the A14 Huntingdon Viaduct, which was recently demolished. This paper describes these two separate activities, covered in Section 2 and 3 respectively.