PSI - Issue 62

Edoardo Proverbio et al. / Procedia Structural Integrity 62 (2024) 285–298 Author name / Structural Integrity Procedia 00 (2019) 000–000

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salt spray or de-icing salts. Voids in the grout also allow the transport of moisture and chlorides along the cable, for example from non-hermetic anchors or construction joints (Menga et al., 2022). Water may also already be present in the post-tensioning cable ducts before grout injection or originate from the grout segregation processes (Permeh et al., 2018). The corrosion of post-tensioned cables, as in prestressed structures with adherent strands, is an aspect to which particular attention is paid not only due to the greater sensitivity to corrosion damage but above all due to the greater structural consequences of their failure. In some conditions steel brittle fracture can occur. Depending on the prevailing corrosion situation and the load conditions, as well as on the properties of the prestressing steel, the following possible fracture conditions must in fact be distinguished: ductile fracture due to exceeding the residual load capacity reduced by generalized or localized corrosion (e.g. pitting); brittle fracture due to hydrogen embrittlement, fracture due to stress corrosion cracking, where it is possible to distinguish between anodic stress corrosion cracking and hydrogen-induced stress corrosion cracking; more rarely failure due to fatigue or corrosion fatigue (Ulf Nürnberger, 2002). Although the conditions that can lead to such events are not very frequent, the attention on these aspects still is high, as remarked since in the early scientific literature (Moore et al., 1970), and technical documents (ACI-ASCE Joint Committee 323, 1958) (Fuzier et al., 2006). Likely, despite corrosion damage being a widespread problem in prestressed concrete structures, cases related to brittle fractures are only a small part of those found in practice (American Concrete Institute. ACI Committee 222, 2014). Most cases observed in the literature also concerned structures where hardened and tempered high-strength steel, which was particularly sensitive to hydrogen embrittlement (Hunkeler et al., 2005), was used, or are consequence to serious manufacturing defects, insufficient or inadequate protection of the reinforcements. In 1992 Podolny (Podolny, 1992), trying to quantify the extent of the problem of corrosion of prestressing steels, made an analysis of the case studies reported in the literature ranging from the 1950s to the early 1990s. In summarizing the findings of the study, he expressed a danger that the favorable conclusions of some early reports, which dismissed the incidence of failure as negligible and due to design defects, improper materials and bad workmanship, might not reflect the real situation. Podolny suggested that the growing number of corrosion incidents reported over time are attributable to the increase in the age of the population of prestressed reinforced concrete structures, to the effects of the substantial increase in the use of anti-icing salts (containing chlorides) began in the 1960s and to the aggressiveness of the marine and urban environments where most of the structures are located. A more recent study on the problems of corrosion in pre-stressed concrete structures was published by the Swiss Federal Roads Office (Hunkeler et al., 2005). The analysis of the case studies was fundamentally based on investigations conducted in Switzerland, although examples from problems recorded in France, Germany, Italy, Belgium and the United Kingdom are also reported. With reference to the small number of failure cases found in Switzerland and directly attributable to hydrogen damage, the authors observed that based on the number of known and documented damages, in international comparison (both in an absolute and relative sense) it seems that the majority part of the damage occurred in Germany. On the one hand, this may be because many damage cases occurred because steels sensitive to stress corrosion cracking (e.g., hardened and tempered steel) and – in the initial phase of prestressed concrete construction – aluminous concrete were used. Furthermore, it can also be stated that in Germany the consumption of prestressing steel was very high and that damage to prestressing systems was reported more openly and systematically than in other countries. However, this situation has given considerable impetus to researches on the phenomenon of stress corrosion cracking and hydrogen embrittlement, especially from the Federal Institute for Materials Research and Testing in Berlin (BAM Berlin) and the University of Stuttgart as well as from national and international standardization bodies like as the AIPRC (CEN, 2003), the FIP (FIP, 1998) and after the merger with the CEB the fib (Manuel Elices et al., 2003), (Fuzier et al., 2006).