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Der Zweck der im vorliegenden Beitrag beschriebenen Untersuchung bestand darin, die Betonstahlbewehrung und nach Möglichkeit auch die Spannglieder auf einer Fläche von insgesamt 8 000 m2 der oberen Brückenfahrbahn des Viadukts “Viadotto Colle Isarco” an der Brennerautobahn mittels Potentialfeldmessungen auf Korrosionserscheinungen zu untersuchen. So wurden Zonen mit hoher Korrosionswahrscheinlichkeit ermittelt und anschließend durch Öffnen und Sandstrahlen inspiziert. Auf der Grundlage dieser Prüfungen konnte abgeschätzt werden, dass auf etwa 9 % der Gesamtfläche eine hohe Korrosionswahrscheinlichkeit in den Spanngliedern gegeben ist. Bei früheren Inspektionen sind bereits gebrochene Spannglieder festgestellt worden. Sämtliche Brüche wurden dabei im Gewindebereich der Verbindungsgelenke festgestellt. In den korrodierten Spanngliedern, die in den “aktiven” Zonen abseits der Verbindungsgelenke lagen, wurden dagegen keine Brüche gefunden. Von den gebrochenen Spanngliedern wurden Proben genommen und zur metallurgischen Analyse ins Labor geschickt. Dabei wurden keine Anzeichen für eine Wasserstoffversprödung des verwendeten Stahls festgestellt. Die Brüche, die in den Spanngliedern bei früheren Inspektionen festgestellt worden sind, wurden höchstwahrscheinlich durch Zyklen mit höherer Belastungsermüdung durch Verkehrslasten in Kombination mit Korrosion aufgrund belastungsempfindlicher Verbindungsgelenke verursacht.Corrosion survey of the bridge deck “Viadotto Colle Isarco”/“Autobahnbrücke Gossensaß” on the Motorway called “Autostrada del Brennero” in North‐ItalyThe scope of this corrosion survey was to detect and quantify zones with high corrosion probability of the normal reinforcement and if possible the prestressed tendons of a total of 8 000 m2 surface area of the upper bridge deck of the “Viadotto Colle Isarco”. This viaduct is part of the A22 Motorway called “Autostrada del Brennero” and lays 10 km's south of the Austrian‐Italian border in Italian territory approximately 1 200 m high in the Alps. In case serious problems were found no recommendations were requested at this point of the survey due to the size and the structural complexity of the concrete structure.Zones with high probability of corrosion were identified by the potentials measured and inspected through scarification and sandblasting. Based on this verification it was estimated an approximate 9 % of the total surface area with high probability of corrosion in the prestressed tendons. This amount is based on adding up all measuring points with a potential being more negative than –450 mV divided by the total amount of measuring points. During previous inspections fractured prestressed tendons were found. All the fractures were found in the threaded region of the coupler joints but no fractures were found in corroded tendons laying in the “active” zones away from the coupler joints. Samples taken from the fractured tendons were sent to the lab for metallurgical analysis and revealed no susceptibility for hydrogen embrittlement of the steel used which has a perlitic microstructure. Fractures found in the tendons in previous inspections are most probably caused by major stress fatigue cycles from traffic loads in combination with corrosion due to the stress‐sensitive couplings. Exactly similar cases (Heerdter crossing in Düsseldorf in 1976) were found in old reports, e.g. published in the technical report 26 “Influence of material and processing on Stress Corrosion Cracking of prestressing steel – case studies” by the International Federation for Structural Concrete (fib) in Lausanne.
Der Zweck der im vorliegenden Beitrag beschriebenen Untersuchung bestand darin, die Betonstahlbewehrung und nach Möglichkeit auch die Spannglieder auf einer Fläche von insgesamt 8 000 m2 der oberen Brückenfahrbahn des Viadukts “Viadotto Colle Isarco” an der Brennerautobahn mittels Potentialfeldmessungen auf Korrosionserscheinungen zu untersuchen. So wurden Zonen mit hoher Korrosionswahrscheinlichkeit ermittelt und anschließend durch Öffnen und Sandstrahlen inspiziert. Auf der Grundlage dieser Prüfungen konnte abgeschätzt werden, dass auf etwa 9 % der Gesamtfläche eine hohe Korrosionswahrscheinlichkeit in den Spanngliedern gegeben ist. Bei früheren Inspektionen sind bereits gebrochene Spannglieder festgestellt worden. Sämtliche Brüche wurden dabei im Gewindebereich der Verbindungsgelenke festgestellt. In den korrodierten Spanngliedern, die in den “aktiven” Zonen abseits der Verbindungsgelenke lagen, wurden dagegen keine Brüche gefunden. Von den gebrochenen Spanngliedern wurden Proben genommen und zur metallurgischen Analyse ins Labor geschickt. Dabei wurden keine Anzeichen für eine Wasserstoffversprödung des verwendeten Stahls festgestellt. Die Brüche, die in den Spanngliedern bei früheren Inspektionen festgestellt worden sind, wurden höchstwahrscheinlich durch Zyklen mit höherer Belastungsermüdung durch Verkehrslasten in Kombination mit Korrosion aufgrund belastungsempfindlicher Verbindungsgelenke verursacht.Corrosion survey of the bridge deck “Viadotto Colle Isarco”/“Autobahnbrücke Gossensaß” on the Motorway called “Autostrada del Brennero” in North‐ItalyThe scope of this corrosion survey was to detect and quantify zones with high corrosion probability of the normal reinforcement and if possible the prestressed tendons of a total of 8 000 m2 surface area of the upper bridge deck of the “Viadotto Colle Isarco”. This viaduct is part of the A22 Motorway called “Autostrada del Brennero” and lays 10 km's south of the Austrian‐Italian border in Italian territory approximately 1 200 m high in the Alps. In case serious problems were found no recommendations were requested at this point of the survey due to the size and the structural complexity of the concrete structure.Zones with high probability of corrosion were identified by the potentials measured and inspected through scarification and sandblasting. Based on this verification it was estimated an approximate 9 % of the total surface area with high probability of corrosion in the prestressed tendons. This amount is based on adding up all measuring points with a potential being more negative than –450 mV divided by the total amount of measuring points. During previous inspections fractured prestressed tendons were found. All the fractures were found in the threaded region of the coupler joints but no fractures were found in corroded tendons laying in the “active” zones away from the coupler joints. Samples taken from the fractured tendons were sent to the lab for metallurgical analysis and revealed no susceptibility for hydrogen embrittlement of the steel used which has a perlitic microstructure. Fractures found in the tendons in previous inspections are most probably caused by major stress fatigue cycles from traffic loads in combination with corrosion due to the stress‐sensitive couplings. Exactly similar cases (Heerdter crossing in Düsseldorf in 1976) were found in old reports, e.g. published in the technical report 26 “Influence of material and processing on Stress Corrosion Cracking of prestressing steel – case studies” by the International Federation for Structural Concrete (fib) in Lausanne.
Experience with prestressed concrete over about half a century has indicated that the corrosion resistance of conventional prestressing steel does not always satisfy, especially the prestressing steels are susceptible to chloride attack (de-icing salts) and hydrogen (hydrogen-induced stress corrosion cracking). On the other hand corrosion agents, such as chloride, condensation water, can penetrate in the concrete and arrive at the surface of steels. Hence, corrosion damage of prestressing steels can happen and, in the extreme cases, the prestressed concrete structure collapsed resulting from the failure of the tendon. In this paper, consideration is made to use high-strength stainless steels as prestressing tendon with bond in concrete. The high-strength stainless steels of qualities 1.4301 (X5CrNi18-10), 1.4401 (X5CrNiMo17-12-2), 1.4436 (X3CrNiMo17-13-3) and 1.4439 (X3CrNiMoN17-13-5) with sequence of increasing austenite stability were investigated. For application in prestressing tendon with bond in concrete the cold-drawn high-strength stainless steel of quality 1.4401 is an optimal proposition regarding its satisfactory resistance against pitting corrosion and stress corrosion cracking (SCC) in structure-related corrosive conditions. The lower alloyed steel 1.4301 has an insufficient resistance against the chloride-induced corrosion because of the lack of molybdenum and the content of deformation martensite due to the strong cold-drawing of its unstable austenitic structure.
Submerged metals are continuously affected by the chemical processes of corrosion, the destructive degradation of metal by chemical or electrochemical reactions within the marine environment (Valenca et al., 2022:2–3; Venugopal, 1994:35). Over time, metal ions at anodic sites defuse into electrolytic solutions from the oxidising reactions occurring at cathodic sites, causing the creation of corrosion byproducts, like rust on iron, and the loss of structural mass. The different reduction reactions in the microstructures of alloys and the imperfections found within refined materials, like carbon slag in steel, are targeted by this process, essentially reverting the chemically unstable materials back to their more stable original forms (Moore III, 2015:192; MacLeod 2016:90–92). The deterioration of metallic shipwreck hulls has become a growing concern within the field of marine conservation as many of the fuel tankers deliberately targeted in WWII threaten to release trapped fuel and chemical cargoes after nearly eight decades of exposure to a range of corrosive environments (Barrett, 2011:4–5). With the deterioration rate of ship hulls averaging at around ±0.1–0.4 mm of loss per year and the thickness of ship deck plates from the 1940s to the 1960s ranging generally from 1–4 cm in thickness, the window to act on the majority of potentially polluting shipwrecks (PPW) before a catastrophic breach occurs is closing (MacLeod, 2016a:8; Beldowski, 2018:249; Masetti, 2012:33; Masetti & Calder, 2014:139).
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