Filtern
Erscheinungsjahr
- 2014 (9) (entfernen)
Dokumenttyp
- Beitrag zu einem Tagungsband (4)
- Vortrag (3)
- Zeitschriftenartikel (1)
- Posterpräsentation (1)
Referierte Publikation
- nein (9) (entfernen)
Schlagworte
- Concrete (2)
- Alkali-silica reaction (ASR) (1)
- Chlorine (1)
- Engineering (1)
- Highly reinforced concrete (1)
- Inspection (1)
- LIBS (1)
- Monitoring (1)
- NDE (1)
- Non-destructuive testing (1)
Eingeladener Vortrag
- nein (3)
The objective of the report is to present the state-of-the art of non-destructive testing methods and technologies for the inspection of thick, heavily-reinforced structures, (e.g. found in nuclear power plants). Wall thicknesses can be in excess of one meter and the structures often have increased steel reinforcement density. The accessibility for any testing method may be limited due to the presence of liners and other components such as cast-in-place items. Testing methods have to provide solutions for tasks such as locating failure (inclusions, corrosion, voids, delaminations) in the structures or the assessment of the condition of the structure in general.
Grouting defects, e.g. in post-tensioned structures or piped anchors may be identified by ultrasonic imaging. Since several years experiences are carried out with false color displayed phase values, which enable distinct localization of ungrouted regions.
In this contribution we report on progress in localizing grouting defects in tendon ducts, when they are only partly grouted and the unfilled part is not orientated into the direction of the measuring surface. This is frequently the case e.g. for box girder structures.
Düring the project specimens containing different types of grouting faults are investigated in Order to optimize measuring and evaluation techniques. A handheld linear array System (commercially available) is applied for fast 2D-measurement and subsequent phase sensitive 3D-imaging (new Software development).
In a large concrete wall specimen tendon ducts and real prestressing Systems containing grouting defects were built in. The ducts are partly covered by non prestressed reinforcement bars in order to investigate its disturbing influence. These included objects were investigated afterwards with the described methods. We report on large area measuring results, which were partly verified by y-radiography. In the frame of practical application results of measuring the position and extend of a blockade within a posttensioned structure are presen ted.
The research project "Ultrasonic Net for Concrete Monitoring (UNeCOM)" aims at developing a methodology for an embedded ultrasonic network for the condition assessment of infrastructure constructions. Civil engineering structures made of concrete, which are located in tectonically active regions or undergo special loading conditions, may require continuous monitoring. It is important to assess the condition of the building and its stability to recognise and classify the effect of a seismic event or evolving damage at early stages before failure occurs. Embedded ultrasonic sensors offer the possibility to detect changes in the material and degradation mechanisms from inside the structure in areas which are difficult or impossible to inspect otherwise. In contrast to conventional ultrasonic testing methods, where the concrete surfaces are scanned with ultrasound probes, this new approach uses sensors, which are embedded into concrete, eliminating the effect of variable coupling conditions between sensors and concrete. This method allows an integral detection of changes in the concrete structure, for example due to seismic activities, to detect mechanical impacts, as well as degradation of the material due to overloading. Such methods have great relevance especially for the monitoring of constructions like power plants, bridges, offshore structures and other structures with high technical safety requirements. The sensor network can be controlled remotely through the internet which is also being used for data transfer. The embedded sensor network is designed to monitor structural damage and concrete degradation globally with high sensitivity.
Laser induced breakdown spectroscopy (LIBS) - visualization of ion transport processes in concrete
(2014)
Laser induced breakdown spectroscopy (LIBS) is a combination of laser ablation and optical emission spectroscopy. Due to the possibility of direct measurements on the sample surface and a minimum of sample preparation investigations of building materials can be conducted quite fast. In combination with a scanning technique (translation stage or scanning mirrors head) the element distributions are evaluated with mm resolution. Thus the heterogeneity of the material may be considered. This is a significant advantage compared to standard procedures. LIBS measurements are also time and cost saving in comparison to standard methods. The automated measurement procedures minimize the liability for errors. All elements are detectable. Results can be quantified after calibration. At BAM LIBS has been successfully applied for the investigation of distribution and transport of different ions in building materials. Quantitative measurements are performed for chlorine, sodium, potassium, sulfur, lithium and hydrogen. In addition the identification of substances and the evaluation of quantitative ratios by means of an integrated marker are possible. An overview about the principle and the possibilities of LIBS investigations of building materials is presented and typical applications are shown. The LIBS technique is close to practical application on-site.
Laser Induced Breakdown Spectrocsopy (LIBS) - Visualizaton of Ion Transport Processes in Concrete
(2014)
Die drei Beispiele zerstörungsfreier Prüfungen an Spannbetonbrücken zeigen unterschiedliche Problemstellungen und deren Lösung mit unterschiedlichen Ansätzen.
Allen drei Beispielen gemeinsam ist die Verwendung kommerzieller Geräte. Diese werden von verschiedenen Anbietern bereitgestellt. Eine weitere Gemeinsamkeit ist, dass die Grundgeräte durch zusätzliche Maßnahmen ergänzt. Erst dann ist der gewünschte Untersuchungserfolg sicher gestellt.
Im ersten Beispiel wurde die vom Auftraggeber geforderte Präzision dadurch erreicht, dass systematische Voruntersuchungen stattfanden. Die Übertragung der Lokalisierung direkt auf die Betonoberfläche stellte sicher, dass keinen Informationsverluste an die nachfolgenden Aufgaben auftraten.
Das zweite Beispiel zeigt den Nutzen von Automatisierung und Kombination von Verfahren. Damit können dem Auftraggeber die notwendigen Angaben über Einbauteile mit großer Detaitreue und leicht verständlicher Visualisierung aufbereitet werden. Der abschließende Bericht zeigt, wie vorhandene Auswertungen sinnvoll durch noch in der Forschung befindliche Ansätze bereichert werden.
Insgesamt ist die zerstörungsfreie Prüfung in der Lage, an Brücken preisrelevante Fragestellungen zu lösen. Voraussetzung hierfür ist eine sorgfältig geplante Vorgehensweise und ein sicheres Verständnis der Grundlage der eingesetzten Geräte und Auswertungsschritte.