PSI - Issue 84

Irene Matteini et al. / Procedia Structural Integrity 84 (2026) 677–685

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1. Introduction Europe manages one of the world’s most extensive and interconnected transportation systems, within which road bridges represent a critical and particularly vulnerable asset. More than 1,200 km of road bridges longer than 100 m are currently in service, a figure that increases significantly when shorter-span structures are considered. A substantial portion of this infrastructure was constructed during the large-scale expansion of the 1960s and 1970s and is now approaching or exceeding its original design life. These ageing structures are increasingly challenged by growing traffic demands and the rising frequency of extreme climatic events. Issues related to bridge conditions have been documented for decades. The EU-funded BRIME project (2001) highlighted alarming levels of structural deficiencies in major European countries, reporting deficiency rates of 39% in France, 30% in Germany, and 37% in the United Kingdom, with reinforcement corrosion identified as a dominant cause [1]. The impacts of insufficient or postponed maintenance are already evident. Deferred interventions lead not only to escalating rehabilitation costs but also to heightened risks in terms of safety and environmental performance. In Germany, for example, the condition of over 1,000 railway bridges has deteriorated to the point where complete replacement is now required [2] . Reinforced and prestressed concrete have historically been the predominant materials used in European bridge construction. As these structures age, the need for systematic condition assessment, continuous monitoring, and proactive maintenance strategies has become increasingly critical. Despite this, maintenance planning is frequently constrained by limited financial resources and suboptimal prioritization strategies. Conventional visual inspections, while still widely adopted, often lack the accuracy and depth necessary to support reliable decision-making—particularly for the assessment of concrete bridge decks, where deterioration processes may remain hidden beneath the surface [3]. As a result, the use of non-destructive testing (NDT) methods has gained momentum, with ground-penetrating radar (GPR) emerging as one of the most promising techniques. GPR is valued for its rapid data acquisition, adaptability, and minimal disruption to traffic operations. It enables non-invasive investigation of concrete bridge decks, providing information on layer thickness, material condition, reinforcement geometry, and the presence of subsurface defects or anomalies. These capabilities make GPR a powerful tool for supporting informed maintenance decisions and mitigating the risk of unexpected structural failures [4]. 1.1. The application of Multichannel GPR (MCGPR) GPR is regarded as one of the most efficient, user-friendly, and least disruptive non-destructive testing (NDT) methods for civil engineering applications, offering versatility across multiple uses [5]. The development of the MCGPR appeared as the next logical evolution for this technology, involving the manufacturing of GPR devices with several antennas mounted onto racks, collecting multiple profiles in a single pass (or swath). Although the first commercial MCGPR arrays date back to the 90s, it was during the 2000s when the first generation of commercial MCGPR systems were released. These systems provide two major advantages over single channel GPR technology: A) Faster data acquisition and B) Higher resolution 3D images, which ultimately allows for faster and less subjective data interpretation However, nowadays MCGPR systems have been mostly used for utility mapping or archaeological surveying and only at a much lesser extent for pavement assessment and bridge deck analysis [6]. The successful implementation of MCGPR for civil engineering had to take into account the higher resolution needed for structural purposes (typically above 2 GHz), and the boundary conditions that this implies in terms of profile spacing (distance between adjacent scans) and trace spacing (distance between each measured point along the profile). Another key requirement is the ability to perform scans only along one direction, thus avoiding the consolidated time-consuming protocol consisting in scanning along both directions of the investigated area. This can be achieved by 1) Dual polarization, that is to say the combined use of antennas positioned in the traditional horizontal HH configuration (optimized for detecting objects orthogonal to the scan) and antennas positioned in the vertical VV configuration (optimized for detecting objects parallel to the scan);and 2) Unprecedentedly dense 3D data (2.5cm channel spacing).