Concrete ageing in hydropower: reducing uncertainty for maintenance and life-extension decisions

For hydropower operators, the key challenge is not recognising concrete degradation, but reliably detecting, quantifying and prioritising it under operational constraints, and linking observations to actionable decisions.

Typical degradation mechanisms like cracking, internal delamination, leakage, ASR, freeze–thaw, are well understood. The difficulty lies in their identification at scale and in representative conditions. Many critical defects remain internal, spatially distributed and poorly correlated with surface observations. This  makes visual inspections insufficient to support decisions about investments or outages.

Assessment campaigns are further constrained by plant realities:

• Restricted access (galleries, underwater zones, confined spaces)
• Limited outage windows
• Safety constraints reducing inspection coverage
• Partial or inconsistent historical data
• Difficulty linking observed defects to structural or operational risk

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Intrusive investigations provide accurate local information but remain time-consuming, costly and difficult to deploy extensively. As a result, they do not capture the spatial variability of degradation, which is often the key parameter for defining rehabilitation scope or assessing residual life.

In this context, non-destructive testing (NDT) is a necessary component of a decision-oriented assessment strategy. Techniques such as ultrasonic tomography, UPV and GPR enable:

• Detection and localisation of internal defects (voids, delamination, cracking)
• Identification of material heterogeneity and degraded zones
• Extension from point data to larger, more representative coverage
• Repeatability for monitoring and trend analysis

Equally important is the execution approach, combining manual, mechanised or robotic deployment depending on accessibility and safety constraints. The value of NDT lies less in individual measurements than in the consistency, coverage and comparability of the dataset, which directly supports engineering interpretation.

However, improved diagnostics only reduce uncertainty if integrated into a structured workflow linking inspection outputs to asset decisions.

A typical approach includes:

1. Consolidation and structuring of available data
2. Risk-based screening to identify critical zones
3. Selection of inspection techniques adapted to expected degradation mechanisms
4. Execution under realistic plant constraints
5. Integrated analysis combining inspection results and engineering judgement
6. Quantification of defects where required (e.g. for structural verification or repair design)
7. Definition of monitoring strategies and performance indicators
8. Identification of corrective and preventive actions

A critical step is root cause analysis, allowing differentiation between superficial degradation and mechanisms that impact durability or structural behaviour. Without this, interventions tend to be either excessive or insufficient, both leading to suboptimal use of outage time and budget.

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Ageing management must also move beyond single inspection campaigns towards a time-based understanding of degradation. Repeatable NDT measurements and targeted monitoring enable tracking of defect evolution, providing a more robust basis for decision-making on maintenance, rehabilitation or life extension.

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In parallel, selected material and repair innovations can complement conventional strategies. For instance, self-healing concrete solutions can be relevant in persistently humid environments, typical of hydropower structures, where crack-sealing mechanisms can be activated. Their value lies in targeted application, supporting durability rather than replacing structural repairs.

Experience from other sectors, particularly nuclear, highlights the benefits of integrating:

• Structured ageing management frameworks
• High requirements for defect characterisation
• Strong linkage between inspection, risk assessment and decision-making

Transferring these practices allows hydropower operators to move from inspection-driven approaches towards risk-informed asset management.

Ultimately, the objective is not to increase inspection effort, but to reduce uncertainty in decisions. This requires combining:

• Inspection methods providing sufficient coverage and repeatability
• Engineering analysis linking defects to performance and risk
• Structured workflows connecting data to actions
• Continuous feedback between inspection, operation and maintenance

Such an approach enables more robust prioritisation of interventions, optimisation of outage planning and better justification of life-extension decisions. These are key factors for ensuring long-term performance and reliability of hydropower assets.