Until now, the Estonian Transport Administration has lacked effective technical tools for evaluating the condition of existing critical bridges and structures with complex designs. In practice, assessments have largely been limited to visible external damage, on the basis of which decisions were made either to repair a bridge or demolish and replace it with a new structure.
Critical defects such as reinforcement corrosion, concrete carbonation, or the failure of post-tensioning tendons can develop deep within a structure, beyond the reach of visual inspection. Traditional non-destructive testing methods, such as ground-penetrating radar (GPR) and ultrasound, lose accuracy when assessing deeper structural elements.
“The lack of precise information has forced bridge owners and managers to make overly conservative decisions, often leading to premature demolition before the end of a bridge’s service life, placing unnecessary strain on both budgets and the environment,” said Tõnis Tagger, Road Infrastructure Environmental Protection Coordinator at the Development Department of the Estonian Transport Administration.
The production of cement, concrete, and steel required for bridge reconstruction generates significant CO₂ emissions. Extending bridge service life through timely repairs and maintenance can substantially reduce these emissions.
Within a project commissioned by the Estonian Transport Administration and funded through the European Union Cohesion Policy 2021–2027 measure “Enhancing Public Sector Innovation Capacity” under the Public Sector Innovation Fund administered by the Government Office, GScan OÜ utilized naturally occurring cosmic radiation to investigate bridge structures.
The objective of experimenting with muon tomography is to provide engineers and decision-makers with objective information about the internal condition of structures. The project was implemented in three consecutive phases, each presenting increasingly demanding technical challenges.
Among other achievements, the project examined the capabilities of muon tomography in underwater environments to enable future assessments of submerged bridge piers. The team also developed automatic object recognition and a methodology for determining steel quantities within structural cross-sections. For the first time anywhere in the world, field measurements using muon tomography were successfully carried out on bridges operating under live traffic conditions, including the Jõgisoo II Bridge, the Munalaskme Bridge, and the Mäo Small Viaduct.
“As both a scientist and an engineer, I am delighted that the Estonian Transport Administration was willing to support the development of an innovative technology created in Estonia. Through this project, we set an example for other countries and created an important springboard for applying muon technology to infrastructure inspections internationally,” said Sander Sein, Lead Engineer at GScan.
The project also resulted in the development of a sustainability calculator based on Life Cycle Assessment (LCA) methodology for preliminary planning of bridge works. The assessment demonstrates the advantages of major rehabilitation and strengthening scenarios compared to complete reconstruction. For example, the major rehabilitation of the Mäo Small Viaduct has approximately 2.5 times lower environmental impact than full reconstruction. In addition, long-term reconstruction projects often require traffic diversions, which can generate substantial additional CO₂ emissions, particularly on heavily trafficked routes.
As part of the project, AS Teede Tehnokeskus conducted a comparative study using conventional concrete cover meters and ground-penetrating radar. The results showed that for thicker structures, GScan’s technology provides a significantly more detailed and informative view of a structure’s internal condition than traditional methods.
Key Benefits of Muon Tomography
Mitigation of risks associated with hidden defects
- The technology can detect defects that are not visible during visual inspections and may remain undetected by other technologies, such as missing tendons inside metallic tendon ducts.
Optimized investment decisions
- If an inspection confirms the integrity of a bridge’s critical structural components, renovation can be chosen instead of demolition, potentially saving millions of euros.
- The economic impact is significant given that funding is currently unavailable for the reconstruction of 87 bridges included in the national road maintenance plan, with an estimated total cost exceeding €300 million.
Support for the green transition
- Extending the service life of bridges is a direct and effective way to reduce the carbon footprint of the construction sector.
The research and development project lasted 18 months and had a total budget of €1.26 million.
