PSI - Issue 78

Irene Matteini et al. / Procedia Structural Integrity 78 (2026) 992–999

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1. Introduction Europe is home to one of the most extensive and complex transport infrastructure networks in the world. Among its key components are over 1,200 kilometres of road bridges exceeding 100 meters in length — a figure that grows substantially when including smaller structures. Much of this infrastructure was erected during the post-war construction boom of the 1960s and 1970s and is now experiencing mounting stress due to increasing traffic volumes and the intensification of extreme weather events. Concerns about structural integrity are not new. As early as 2001, the EU-funded BRIME project revealed worrying trends: in France, Germany, and the UK, highway bridges showed deficiency rates of 39%, 30%, and 37%, respectively — largely due to reinforcement corrosion [1]. The consequences of deferred maintenance are already apparent. Delays not only increase future repair costs but also pose significant environmental and safety risks. In Germany alone, more than 1,000 railway bridges have deteriorated to such a degree that they must now be entirely rebuilt [2]. Historically, European bridge construction has relied heavily on reinforced and prestressed concrete. With the advancing age of these structures, the importance of regular monitoring, preventative maintenance, and timely intervention has become paramount. However, effective maintenance is often hampered by limited budgets and inefficient resource allocation. Traditional visual inspections, though widely used, often fail to provide the precision required for sound decision making — particularly in evaluating concrete bridge decks [3]. This has led to increasing interest in non-destructive testing (NDT) techniques, especially ground-penetrating radar (GPR). Recognized for its efficiency, versatility, and minimal operational disruption, GPR is emerging as a critical tool for assessing structural health. GPR facilitates the rapid and non-invasive evaluation of concrete bridge decks, enabling engineers to measure layer thicknesses, assess material quality, map reinforcement layouts, and identify hidden defects or anomalies — all crucial for informed maintenance planning and the prevention of future failures [4]. 1.1. The application of Multi-channel Georadar 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 multi-channel georadar (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 multichannel GPR (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 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). In general terms, the Nyquist Criterion [7] establishes the fundamental guidelines for acquiring GPR data to ensure the desired resolution without information loss. From a practical standpoint, however, it is only in recent years that