Assessing Bridge Infrastructure Using Muon Tomography: Insights from Our 18-Month Project with the Estonian Transport Administration

GScan has successfully concluded an 18-month collaborative project with the Estonian Transport Administration and the Government Office's Public Sector Innovation Fund. The initiative evaluated how muon tomography—a non-destructive imaging technique utilising natural cosmic particles—can be used to scan the interior of complex concrete and steel bridges to optimise maintenance and safely extend their service life.

The Challenge of Hidden Structural Defects

Traditional bridge inspections rely heavily on visual assessments, ground penetrating radar (GPR), and ultrasound. While these methods are effective for surface-level and shallow subsurface evaluations, they lose accuracy when scanning deep inside thick, heavily reinforced concrete structures.

Critical structural issues—such as reinforcement corrosion, concrete carbonation, or voids and missing grout inside post-tensioning cable ducts—often occur where traditional non-destructive testing (NDT) tools cannot reach. Without highly precise internal data, infrastructure managers are frequently forced to make conservative decisions. This can lead to the premature demolition and replacement of bridges that could otherwise be safely repaired, placing an avoidable financial burden on public budgets and increasing carbon emissions.

Project Scope and assessing bridge infrastructure

The €1.26 million project, funded by the European Union Cohesion Policy 2021–2027, was executed in three progressive phases to test the limits of muon imaging technology.

Significantly, the project achieved a milestone by conducting muon tomography field measurements on active bridges while they remained fully open to live traffic. Field scans were successfully completed at three sites in Estonia:

• Jõgisoo II Bridge

• Munalaskme Bridge

• Mäo Small Viaduct

Beyond standard scanning, the project investigated the technology's capabilities in aquatic environments to lay the groundwork for future underwater column inspections. The team also developed automated object detection methodology to accurately determine the volume and distribution of steel within a structure's cross-section.

Comparative Performance Analysis

To verify data accuracy, AS Teede Tehnokeskus conducted a side-by-side comparative study evaluating GScan’s technology against standard tools for assessing bridge infrastructure, including protective layer gauges and conventional GPR. The study confirmed that when dealing with thicker concrete elements, muon tomography provides a significantly more detailed, high-resolution overview of internal structural components than existing NDT alternatives.

Measuring Environmental Impact

The carbon footprint of producing the cement, concrete, and steel required for full bridge reconstructions is substantial. To address this, the project included the development of a Life Cycle Assessment (LCA) sustainability calculator designed for preliminary bridge work planning.

The LCA metrics highlighted the clear environmental advantages of targeted overhauls over complete replacements. For example, opting to repair and reinforce the Mäo small viaduct instead of rebuilding it entirely resulted in a 2.5 times smaller environmental footprint. Additionally, extending the life of existing structures eliminates the significant secondary CO₂ emissions generated by traffic diversions during lengthy reconstruction closures.

Primary Outcomes for Infrastructure Managers

• Early Defect Identification: Detects internal anomalies (e.g., missing wire or voids in metal cable channels) that are invisible to the eye and undetectable via shallow radar.

• Capital Optimisation: Validates the structural integrity of critical nodes so managers can confidently invest in targeted renovations rather than costly demolitions.

• Green Transition Support: Maximises the operational lifespan of existing infrastructure, directly reducing material consumption and the transport sector's broader carbon footprint.

The complete data sets and comprehensive survey reports from these field tests are available through the Estonian Transport Administration.