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- Chloride (2)
- Durability (2)
- Alkali activated cement (1)
- Alkali-activated materials (1)
- Betondickglasfenster (1)
- Carbonation (1)
- Concrete-glass windows (1)
- Corrosion (1)
- Dalle-de-verre (1)
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Organisationseinheit der BAM
Concrete-glass windows or commonly referred to as “Dalle de Verre” windows are prevalent in historical monuments across Europe. “Dalle de Verre” windows were made by placing cut stained glasses, of various shapes and sizes, into a steel reinforced concrete frame. In addition to the steel reinforcement, a few steel wires run across the concrete elements to hold the glass windows into place. Much of these structures have been damaged due to carbonation of the thin concrete covers and consequent corrosion of the steel reinforcement; and exhibit several cracks due to the expansive nature of corrosion products formed at the steel–concrete interface. This study focussed on understanding the efficacy of electrochemical realkalisation in reinstating the passive state of the steel reinforcement embedded in such concrete glass windows. Simulant “Dalle de Verre” windows (representative of windows at Kaiser-Wilhelm Gedächtniskirche) were produced using different cements with a water/cement ratio of 0.6 and carbonated under accelerated conditions. Post carbonation, the concrete glass windows were electrochemically realkalised using a sacrificial anode. The influence of highly alkaline conditions due to electrochemical realkalisation on the glass-concrete interface has also been investigated. This study shows that the passive state of the steel reinforcement in “Dalle de Verre” windows, particularly at the Kaiser-Wilhelm Gedächtniskirche (memorial church) in Berlin, can be reinstated using the electrochemical realkalisation method.
The pore fluid within many concretes is highly alkaline and rich in reduced sulfur species, but the influence of such alkaline-sulfide solutions on the surface film formed on steel reinforcement is poorly understood. This study investigates the critical role of HS− in defining mild steel passivation chemistry. The surface film formed on the steel in alkaline-sulfide solutions contains Fe(OH)2 and Fe–S complexes, and the critical chloride concentration to induce corrosion increases at high sulfide concentration. However, this behavior is dependent on the duration of exposure of the steel to the electrolyte, and the nature of the sulfidic surface layer.
Die Kaiser-Wilhelm-Gedächtniskirche (KWG) gilt als eine der wichtigsten Sehenswürdigkeiten Berlins in der City West und als ein herausragendes Beispiel für die „Dalle de Verre“ Verglasungen in sakralen Gebäuden. Der vorliegende Beitrag widmet sich der Fassade und den Glasfenstern des neuen Glockenturms, wobei die beschriebenen Szenarien aufgrund der annähernd gleichen Bauweise der restlichen neuen Baukörper in weiten Teilen starke Analogien aufweisen und insofern übertragbar sind.
The service-life of steel-reinforced concrete structures is primarily determined by the ability of the concrete cover to resist chloride ingress. With limited literature available on the ingress of chloride into alkali-activated slags (AAS) under service conditions, it is critical that this is described by appropriate models. This paper describes an interactive software framework to relate chloride ingress into AAS with the chemistry of the concrete cover, by considering the chloride binding capacity and porosity of the binder as a function of time, based on thermodynamic calculations of the phase assemblage as a function of slag and activator composition. This provides a major step towards developing the ability to predict the ingress of chlorides in alkali-activated concretes from a sound theoretical basis, which is essential in providing confidence in the durability of these materials in essential infrastructure applications.
The steel–concrete interface (SCI) is known to influence corrosion of steel in concrete. However, due to the numerous factors affecting the SCI—including steel properties, concrete properties, execution, and exposure conditions—it remains unclear which factors have the most dominant impact on the susceptibility of reinforced concrete to corrosion. In this literature review, prepared by members of RILEM technical committee 262-SCI, an attempt is made to elucidate the effect of numerous SCI characteristics on chloride-induced corrosion initiation of steel in concrete. We use a method to quantify and normalize the effect of individual SCI characteristics based on different literature results, which allows comparing them in a comprehensive context. It is found that the different SCI characteristics have received highly unbalanced research attention. Parameters such as w/b ratio and cement type have been studied most extensively. Interestingly, however, literature consistently indicates that those parameters have merely a moderate effect on the corrosion susceptibility of steel in concrete. Considerably more pronounced effects were identified for (1) steel properties, including metallurgy, presence of mill scale or rust layers, and surface roughness, and (2) the moisture state. Unfortunately, however, these aspects have received comparatively little research attention. Due to their apparently strong influence, future corrosion studies as well as developments towards predicting corrosion initiation in concrete would benefit from considering those aspects. Particularly the working mechanisms related to the moisture conditions in microscopic and macroscopic voids at the SCI is complex and presents major opportunities for further research in corrosion of steel in concrete.
Alkalisch aktivierte Bindemittel (AAB) und Betone können herkömmliche Zemente beziehungsweise Betone potentiell in vielen Anwendungen ersetzen und dadurch den CO2-Fußabdruck der Bauindustrie wesentlich verkleinern. Zur Untersuchung der Stahlkorrosion in bewehrten („armierten“) Betonbauteilen werden elektrochemische Methoden wie Messungen des Freien Korrosionspotentials, des Polarisationswiderstands oder von Stromdichte-Potential-Kurven eingesetzt. Diese Methoden und die etablierten Grenzwerte zur Detektion von Korrosion sind für die Anwendung bei herkömmlichen Zementen beziehungsweise Betonen entwickelt und erprobt worden. Neue Forschungsergebnisse demonstrieren, dass Unterschiede zwischen den Porenlösungszusammensetzungen von herkömmlichen Zementen und bestimmten AAB sowie anderen schlackehaltigen Zementen erhebliche Unterschiede bei den Ergebnissen der elektrochemischen Messungen bewirken und damit zur fehlerhaften Detektion von Stahlkorrosion führen können. Ursache hierfür sind vor allem reduzierte Schwefelspezies in den Porenlösungen von AAB und anderen schlackehaltigen Zementen.