PSI - Issue 84

Davide Caliò et al. / Procedia Structural Integrity 84 (2026) 513–520

518

As shown in Fig. 2, areas characterized by higher temperatures compared to the surrounding context, with values close to 18 °C (the maximum temperature recorded during the survey), can be interpreted as surfaces potentially associated with partially bulging concrete cover, within which air pockets may form. Over time, such conditions may promote the evolution toward concrete cover detachment, with consequent exposure of the reinforcement. These anomalies are clearly identifiable in the three-dimensional thermal reconstruction. Conversely, lower-temperature anomalies tend, in several cases, to be spatially associated with areas affected by surface degradation processes. In some instances, these anomalies coincide with zones where concrete cover detachment and reinforcement exposure are visually evident; in other cases, as highlighted in Fig. 3c, cold thermal anomalies were detected even in the absence of exposed reinforcement, suggesting the possible presence of early-stage processes of moisture ingress, corrosion, and reinforcement expansion, preceding macroscopic concrete cover detachment. Overall, the thermal analysis allowed the reconstruction of an evolutionary scheme of structural degradation that is not fully appreciable through visual inspection alone. Within this framework, an initial phase of concrete cover bulging, associated with the presence of thermal hotspots, can be distinguished, followed by an intermediate phase in which the reinforcement, although not yet exposed, becomes detectable through linear negative thermal anomalies. The evolutionary process ultimately culminates in the phase of concrete cover detachment and spalling, which is clearly visible in both RGB imagery and IRT data. IRT therefore provides an additional informational contribution compared to RGB images alone, enabling not only the recognition of areas already affected by evident degradation but also the identification of structural portions potentially involved in the early stages of corrosion processes. This approach allowed a more comprehensive assessment of the conservation state of the piers, supporting the identification of the most vulnerable zones as well as those not yet significantly affected by degradation phenomena. The results of the geological and geomorphological analysis show that the lithological setting and local morphology significantly influence the geo-structural behaviour of the slopes shaped by the stream and, consequently, of the hillsides on which the abutments of the Cantera viaduct are structurally founded. Within this framework, the analysis of geomorphological criticalities focused on the abutment in the direction of Syracuse. The integration of UAV-based RGB and IRT surveys allowed the identification of two relevant issues. Evidence of instability was recognised along the north-western slope immediately adjacent to the abutment. The signals of this instability are clearly visible in aerial imagery and three-dimensional models, as shown in Fig. 3. In particular, the presence of bedding discontinuities enhances free fall movements at the most jutting rock mass portions, while high angle discontinuity sets mainly drive other failure patterns, such as toppling. At the top of the slope, at approximately 17 m from the roadway (Fig. 3a–b), a linear feature about 20 m in length was identified. This is recognisable in both the RGB data and the thermograms acquired under both daytime and nighttime conditions (Fig. 4a–b). This anomaly may represent a preferential direction for surface water runoff, which could coincide with peculiar morphological features related to the rock mass geostructural conditions. However, additional investigations are required to determine whether this hypothesis can be confirmed. A further significant geo-structural element is located approximately 8 m downslope from the main anomaly and about 25 m from the viaduct abutment (Fig. 3). This feature consists of a cavity attributable to a collapse event that affected an area of approximately 100 m². The digital geo-structural analysis performed on the unstable sector allowed the identification of five main discontinuity sets, shown in Fig. 3c. Based on subsequent kinematic analyses, four potential failure mechanisms were recognised. In particular, the discontinuity set with attitudes of 74/153 (dip/dip direction) shows 100% of the poles falling within the critical zone for flexural toppling. Similar mechanisms are also present on the opposite slope, highlighting a systematic structural pattern that promotes failure initiation, toppling, and subsequent collapse of sometimes significant rock volumes. 4.3 Geological and geomorphological features