Präsentation
Filtern
Dokumenttyp
- Vortrag (8)
- Posterpräsentation (4)
Referierte Publikation
- nein (12)
Schlagworte
- Faserverstärkter Beton (FRC) (3)
- Feuchtigkeitsmessung (3)
- Röntgencomputertomographie (CT) (3)
- Digitale Bildkorrelation (DVC) (2)
- In-situ Prüfverfahren (2)
- SealWasteSafe (2)
- Alkali-Activated Material (1)
- Alkali-Silica Reaction (ASR) (1)
- Alkali-silica-reaction (ASR) (1)
- Brunauer-Emmett-Teller (BET) Method (1)
Organisationseinheit der BAM
Eingeladener Vortrag
- nein (8)
Intensified Alkali-Silica Reaction (ASR) damage has occurred on German roadways in recent years, leading to requirements for compulsory pre-construction investigation of aggregate alkali sensitivity using concrete tests with external alkali supply. However, since these tests are time-consuming and cost-intensive, there is interest in replacing them with a solubility test on pure aggregate in 0.1 M KOH solution at 80°C with a defined NaCl content (1wt.-%). In this context, the influence of aggregate pore structure on SiO2 and Al2O3 solubility was investigated in this project. This paper compares the results of porosity studies with X-ray Computed Tomography (3D-CT) and the Brunauer-Emmett-Teller (BET) method on individual quarried and river gravel granules of both rhyolite and greywacke. For visualization and quantification of both externally accessible and fully enclosed surfaces of granules using X-ray 3D-CT, special software tools were developed. The results demonstrated that the river gravel granules had significantly larger externally accessible surfaces than the quarried granules. BET measurements on individual stones showed, as expected, that measured surfaces were about three orders of magnitude larger than those from the X-ray 3D-CT analyses due to the higher spatial resolution of BET. There was no apparent correlation between the X-ray 3D-CT and BET surface areas. Mercury porosimetry measurements indicate that this may be due to the presence of significant porosity below the spatial resolution of the X-ray 3D-CT. A comparison of SiO2 and Al2O3 solubility measurements with the X-ray 3D-CT and BET surface area data resulted only in weak, inconclusive correlations, indicating the need for further experimental investigation.
Die Präsentation demonstriert die Fähigkeiten der Röntgencomputertomographie (CT) zur Identifizierung quantitativer Materialeigenschaften wie Faserorientierung und Korrosionsverteilung sowie die Implementierung von CT-Daten innerhalb numerischer Simulationen. Die besondere Stärke der CT, als zerstörungsfreies Prüfverfahren, ermöglicht es, das Materialverhalten und den Versagensprozess während mechanischer, hydraulischer und thermischer Prozesse zu beobachten. Die Ergebnisse einer Reihe von Ex-situ und In-situ Testprogrammen unter Bedingungen wie mechanische Belastung, Wassertransport und thermische Exposition, stellen die Nutzungsmöglichkeiten dieser Verfahren in Kombination mit der CT in eindrucksvoller Weise dar.
The proposed BAM project SealWasteSafe will advance the state of the art for the construction and monitoring of safe sealing systems for underground repositories of radioactive or toxic waste. During this project, a novel salt concrete exhibiting neither significant cracking nor shrinkage will be optimized for use in the sealing systems. The composition of this material will be based on alkali-activated materials, which are characterized by particularly small thermal deformations during the hardening reaction. Quality assurance and continuous monitoring systems developed during this project will be demonstrated not only for high reliability, but also for resistance to highly alkaline environments and to water intrusion along cables or at sensor locations. A variety of sensors will be used in combination with wireless Radio Frequency Identification (RFID) technology to record moisture, temperature, and, if necessary, corrosion activity within the sealing system. Distributed Fibre Optic Sensor (FOS) technology will also be used for strain, temperature, and moisture content measurement. Ultrasound-based measuring methods will be utilized for the detection of cracks and delaminations. Additionally, digital image correlation and acoustic emission analysis will be used for deformation measurements and crack detection. A novel borehole probe and advanced ultrasound imaging techniques will be further developed to track cracks and delaminations within the host rock in 3D. The surface-based Large Aperture Ultrasound System (LAUS) will also be utilized to detect cracks and delaminations deep below the exterior surface of the sealing system. Although the focus of this project will be on the host rock salt, the resulting technologies will be intentionally developed in a way that facilitates their adaptation to other host rocks.
The closure of underground nuclear waste disposal facilities requires reliable gas- and water-tight engineered barriers. In Germany, barriers made from salt concrete have been evaluated in full scale. While the barriers seem to fulfill the requirements regarding permeability, some unexpected cracks have been detected at the surface and at depth. In cooperation between the Federal Company for Radioactive Waste Disposal (BGE) and the Federal Institute for Materials Research and Testing (BAM), several experiments have been carried out to evaluate the applicability for ultrasonic measurements in crack detection and general quality assurance. Both commercial instruments and specially developed devices have been tested on site.
Using commercial ultrasonic echo devices designed for concrete inspection it was possible to detect cracks and objects in salt concrete up to a depth of 2 m. The check for delamination in shotcrete is another field of application. A unique device available at BAM, the wide aperture, deep penetration instrument LAUS, was able to locate cracks and objects up to a depth of 8 m so far, which is thought to be a record for ultrasonic echo measurements in concrete. Adapted imaging procedures, partly adopted from geophysics, helped to reveal 3D structure at depth.
In addition, we have developed ultrasonic probes to be deployed in boreholes, currently at up to 20 m depth. They can collect information on cracks and other features in a radius of about 1.5 m around the borehole in the current version and might be used in echo or transmission mode. Evaluation experiments have been performed at an experimental barrier at the ERAM site in Morsleben, Germany. The results showed several empty and injected cracks as well as built-in instrumentation. The results have been verified using borehole endoscopy as well as core examination and will be used to set up a reliable quality assurance system for engineered barriers. All instruments are based on ultrasonic shear wave transducers with a frequency range between 25 kHz and 100 kHz. Current research focuses on the improvement of the hardware (e. g. optimization of array characteristics) and imaging techniques such as Reverse Time Migration, both aiming at the improvement of depth of penetration, resolution and probability of detection.
Für die Festigkeit von faserverstärkten Betonen spielt die beim Gießvorgang hervorgerufene Faseranisotropie eine wichtige Rolle. In den computertomographischen Aufnahmen lässt sich die anhand der Eigenvektoren der Hessianmatrix an der Faser ermittelte räumliche Orientierung der Fasern berechnen und im sphärischen Koordinatensystem darstellen.
Mit für die CT-Anlagen ausgelegten Prüfeinrichtungen ist es möglich mechanische Belastungen, Wärmeeinwirkung und Feuchtetransport in Betonproben während einer CT-Messung durchzuführen. Die Analyse dieser In-situ Messungen erfordert zum Teil speziell auf die Erfordernisse angepasste Auswerteverfahren. Dazu zählen die automatische Rissdetektion oder die Korrektur der Streustrahlung bei der Wasseraufnahme.
Beton ist das meistbenutzte Baumaterial der Welt. Sein Herstellungsprozess ist auch für schätzungsweise 5% der globalen Kohlenstoffemissionen verantwortlich. Daher können selbst kleine Verbesserungen in der Festigkeit oder Haltbarkeit zu einer erheblichen Verringerung der Bau- und Wartungskosten, der Umweltschäden und der Gefahr für die Menschen führen. Um das grundlegende Verhalten dieses Materials zu verstehen, ist es notwendig, seine Leistung während thermischer, chemischer und mechanischer Prozesse (d. h. in-situ) zu beobachten. Es wird eine zerstörungsfreie Messmethode benötigt, die in der Lage ist, nicht nur Änderungen des Materials wie Feuchtigkeitsumverteilung, Korrosion und Dehnung zu messen, sondern auch die innere Struktur des Materials im Dreidimensionalen aufzulösen, so dass Versagensmechanismen und Transportphänomene direkt auf bestimmte Eigenschaften der heterogenen Materialstruktur bezogen werden können (wie z.B. die Übergangszone zwischen Gesteinskörnungen und Zementstein oder die Orientierung von eingebetteten Fasern).
Die Röntgencomputertomographie (CT) hat sich als ideal für solche Zwecke erwiesen. Neuere Forschungen an der BAM werden vorgetragen, die die Fähigkeiten der CT zur Identifizierung quantitativer Materialeigenschaften wie Faserorientierung, Rissoberfläche, Korrosionsverteilung und Änderungen des volumetrischen Feuchtigkeitsanteils demonstrieren. Der Nutzen dieser leistungsstarken Analysewerkzeuge wird dann anhand der Ergebnisse einer Reihe von Ex-situ und In-situ Testprogrammen für Bedingungen wie mechanische Belastung, Wassertransport und thermische Exposition gezeigt. Speziell entwickelte In-situ Testmaschinen für diese verschiedenen Testprogramme werden ebenfalls beschrieben. Die von der CT gelieferten quantitativen Charakterisierungsinformationen haben sich als ideale Grundlage für die Kalibrierung bzw. Validierung von numerischen Simulationen erwiesen. CT ist auch wesentlich für die Beantwortung von vielen anwendungsspezifischen Fragen, u.a. wie sich verschiedene Gießverfahren auf die Materialleistung auswirken, welche Mineralien sich als Zuschlagstoffe anfällig für langfristige chemische und hydraulische Prozesse erweisen und wie Polymerfasern den Druckaufbau in Beton während der thermischen Belastung beeinflussen.
Um das grundlegende Verhalten des Betons zu verstehen, wird eine zerstörungsfreie Messmethode benötigt, die in der Lage ist, nicht nur Änderungen des Materials wie Feuchtigkeitsumverteilung, Korrosion und Dehnung zu messen, sondern auch die innere Struktur des Materials im Dreidimensionalen aufzulösen, so dass Versagensmechanismen und Transportphänomene direkt auf bestimmte Eigenschaften der heterogenen Materialstruktur bezogen werden können. Die Röntgencomputertomographie (CT) hat sich als ideal für solche Zwecke erwiesen. Diese Präsentation demonstriert die Fähigkeiten der CT zur Identifizierung quantitativer Materialeigenschaften wie Faserorientierung, Rissoberfläche, Korrosionsverteilung und Änderungen des volumetrischen Feuchtigkeitsanteils. Durch die Beschreibung der Ergebnisse einer Reihe von Ex-situ und In-situ Testprogrammen für Bedingungen wie mechanische Belastung, Wassertransport und thermische Exposition, sind auch die Nutzungsmöglichkeiten von diesem Verfahren dargestellt.
This poster provides an overview of ultrasonic investigations of an engineered test barrier at ERAM Morsleben, which were completed as part of contractual work with the Bundesgesellschaft für Endlagerung mbH (BGE). This includes both experiments with the Large Aperture Ultrasound System (LAUS) and the ultrasonic borehole array. Also included in the poster is a description of the planned BAM thematic project “SealWasteSafe”. In particular, the proposed geopolymer materials are described and future research requirements are detailed.
Although concrete itself is not a combustible material, concrete mixtures with high density, such has high-performance concretes (HPCs), are susceptible to significant damage during fires due to explosive spalling. Past research has shown that the inclusion of polymer fibers in high density concrete can significantly mitigate fire damage due to the contribution of the fibers to increased permeability levels at high temperature. This allows vapor pressures caused by the evaporation of internal water during fire to escape from the material without causing significant spalling. Recent microscopic investigations have also shown that the addition of polypropylene (PP) fibers to high-density HPC with a high amount of fine-aggregate has a considerable influence on the nature and character of crack formation due to autogenous shrinkage. Initial cracks, which originate from the fiber beds, undergo further expansion and propagation when concrete is subjected to thermal exposure in excess of 170 °C. It is thus of interest to determine whether the resulting cracks join the adjacent fiber beds and therefore contribute to a significant increase in the permeability of the concrete, which is directly correlated to lower pore pressures and reduced spalling during fire.
In this study, X-ray Computed Tomography (CT) was applied to provide a clear demonstration of the interaction between polymer fibers and cracking during thermal exposure. For this purpose, two concrete samples containing different polymer fiber types were subjected to incremental application of a defined thermal exposure. CT images were acquired before and after each thermal exposure and powerful image processing tools were used to segment the various material components, such as polymer fibers, cracks, aggregates and cement matrix, in each image. This enabled a detailed analysis of crack formation and propagation as well as the visualization and quantification of polymer fiber characteristics within the concrete. This paper will provide a description of the distribution and orientation characteristics of the polymer fibers within each sample obtained through the CT-based analysis. Using these results, the impact of fiber distribution and orientation characteristics on actual cracking geometries have been measured and visualized. This paper will also provide recommendations for further optimization of the selected materials and propose improved methods for future CT-based analysis techniques.
The water-transport characteristics of concrete have a major impact on its resistance to damaging chemical processes such as Alkali-Silica-Reaction (ASR). Water transport in samples of damaged and undamaged concrete was measured using in-situ CT. The resulting measurements of water-front movement relative to time and the change in 3D-moisture distribution within the samples, are needed for calibration and validation of water-transport numerical models.