PSI - Issue 84

Anna Bontempi et al. / Procedia Structural Integrity 84 (2026) 1039–1046

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1. Introduction A significant portion of the existing reinforced concrete (RC) and prestressed concrete (PC) infrastructure was designed and constructed according to building codes primarily focused on structural safety and serviceability, with limited attention devoted to durability issues. The observed long-term behavior of concrete structures exposed to aggressive environmental conditions has progressively highlighted the inadequacy of these assumptions, emphasizing the need to assess existing structures by explicitly accounting for durability-related deterioration processes and the cumulative damage developed over decades of service (Walraven, 2021). Corrosion-induced degradation may result in concrete cracking and spalling, loss of reinforcement cross-section, deterioration of bond conditions, and a consequent reduction in strength and ductility. In this context, the assessment of existing RC and PC structures has become a critical issue for infrastructure management, particularly for bridges that have already exceeded or are approaching service lives of 50 years or more (Di Prisco, 2019). Reliable evaluation of residual capacity is therefore essential to support decisions regarding maintenance, strengthening, or replacement strategies. Despite the relevance of this problem, experimental evidence based on full-scale structural elements subjected to long-term natural corrosion remains limited. Opportunities to perform destructive tests on real-scale members removed from service are rare. Some contributions have addressed the residual strength and structural response of naturally corroded prestressed and reinforced concrete bridge beams, such as (Rogers et al., 2012; Recupero and Spinella, 2019; Belletti et al., 2020; Savino et al 2023). Even a smaller amount of experimentation focuses on the experimental evaluation of strengthening techniques applied to real-scale, long-term deteriorated elements. From a practical standpoint, strengthening existing structures represents a potentially advantageous alternative to full replacement. Beyond direct construction costs, replacement interventions often involve substantial indirect costs related to traffic interruption, detours, and broader socioeconomic impacts, which may be particularly critical for strategic transport infrastructure. Strengthening solutions, when technically feasible, may therefore offer significant economic and logistical benefits while extending the service life of existing structures. Within this framework, the present study investigates the strengthening of a historic RC bridge beam with a T shaped cross-section that remained in service for approximately 90 years. An innovative strengthening technique combining carbon fiber–reinforced polymer (CFRP) bars and a fiber-reinforced mortar with polypropylene fibers (FRM-PP) is experimentally evaluated. The main goal is to assess the residual capacity of the existing member and to quantify the increase in load-bearing performance provided by the strengthening system, thereby contributing experimental evidence on the feasibility of strengthening as an alternative to full structural replacement for aging concrete infrastructure. 2. Experimental program The experimentation involved one 90 years old RC bridge girder, which came from the dismantling process of the Fiume Garza overpass in Brescia. The existing structure was characterized by a single-span scheme with simply supported beams. These beams had a T-shaped cross-section. The original structure was entirely replaced with precast PRC beams, and the existing beams were demolished. However, the Municipality of Brescia donated one specimen to the university for research purposes. The research aims to evaluate the applicability of an innovative strengthening technique which, in certain cases, may be economically advantageous compared to replacement, while still ensuring adequate performance in terms of structural resistance. The deterioration conditions observed in a portion of the bridge are presented in Figure 1a. The girder under study exhibited extensive concrete cover loss and significant corrosion affecting both the longitudinal and transverse reinforcement (Figure 1b).