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Eingeladener Vortrag
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This working paper summarises the current state of knowledge and research on the application of sensors in road pavements, designed to record input quantities and characteristics for structural assessment. In this working paper, sensors generally refer to technical equipment that can used to record the values of physical quantities and display them for interpretation.
The working paper deals with every type of sensor that is permanently connected to the road, i.e. sensors that are installed – in the bound and unbound courses of the superstructure as well as in the sub-base/sub-structure, – next to or above the road (for example on masts) and can contribute to structural recording and its subsequent assessment. This can also include sensors that are primarily used for a different purpose (e.g. traffic control). However, this working paper only describes the application of sensors that are installed primarily for other purposes for the sake of completeness; special publications (e.g. Notes on detection technologies in road traffic) are available for the respective installation situations.
Bei der Erhaltung von Stahlbetonbauwerken ist der Chloridgehalt im Beton ein wichtiger Parameter zur Festlegung geeigneter Instandsetzungsmaßnahmen. Die bisher etablierten Verfahren basieren auf der nasschemischen Analyse einer Probe, Bohrmehl oder aufgemahlener Segmente eines Bohrkerns. Das Verfahren liefert einen Chloridgehalt je Tiefensegment, was mit einer starken Homogenisierung der Probe einhergeht, wodurch detaillierte Informationen zu Chloridunterschieden im Millimeterbereich verloren gehen. Eine alternative Methode ist die laserinduzierte Plasmaspektroskopie (LIBS), die nicht nur die quantitative ortsaufgelöste Bestimmung des Chloridgehalts im Bezug zur Zementmasse ermöglicht, sondern auch simultan detaillierte Informationen über die Verteilung vieler anderer chemischer Elemente liefert. Die räumliche Auflösung liegt in der Regel im Bereich von einigen Millimetern, kann aber bei Bedarf auf 0,1 mm oder weniger erhöht werden. Das neue Merkblatt B14 „Quantifizierung von Chlorid in Beton mit der laserinduzierten Plasmaspektroskopie (LIBS)“ der Deutschen Gesellschaft für Zerstörungsfreie Prüfungen (DGZfP) regelt und vereinheitlicht erstmals die zuverlässige und reproduzierbare Ermittlung des Chloridgehalts mit LIBS. In diesem Beitrag wird das Merkblatt vorgestellt und anhand praktischer Anwendungsbeispiele das Potenzial von LIBS für Fragestellungen in der Betonerhaltung verdeutlicht.
-Über 80 Mio. Schwellen im deutschen Schienennetz verbaut
-Lebensdauer einer Schwelle beträgt ca. 20 bis 50 Jahre
-Über 2 Mio. Schwellen werden jährlich ausgetauscht, obwohl die Mehrzahl noch intakt ist
-Zustandsbewertung mittels ZfP kann Ausschuss verringern
-Schadhafte Schwellen könnten mittels ZfP frühzeitig im Gleis erkannt werden, um Gefahren und Unfälle abzuwenden
This technical note highlights the fact that CF-LIBS algorithms work in mole fractions, while results of spectrochemical analysis are usually reported in mass fractions or mass percent. Ignoring this difference and not converting mole fractions to mass fractions can lead to errors in reported concentrations determined by the CF-LIBS method and inadequate comparison of these concentrations with certified concentrations. Here, the key points of the CF-LIBS algorithm are reproduced and the formulae for converting a mole fraction to a mass fraction and vice versa are given. Several numerical examples are also given, which show that the greater the difference between the molar mass of an individual element in a sample and the average molar mass, the greater the discrepancy between the mole and mass fractions.
Additive manufacturing of concrete structures is a novel and emerging technology. Freecontouring in civil engineering, which allows for entirely new designs, is a significant advantage. Inthe future, lower construction costs are expected with increased construction speeds and decreasingrequired materials and workers. However, architects and civil engineers rely on a certain quality ofexecution to fulfil construction standards. Although several techniques and approaches demonstratethe advantages, quality control during printing is highly challenging and rarely applied. Due to thecontinuous mixing process commonly used in 3D concrete printing, it is impossible to exclude varia-tions in the dry mixture or water content, and a test sample cannot be taken as a representative samplefor the whole structure. Although mortar properties vary only locally, a defect in one layer duringprinting could affect the entire integrity of the whole structure . Therefore, real-time process monitor-ing is required to record and document the printing process.At the Bundesanstalt für Materialforschung und -prüfung (BAM) a new test rig for the additive man-ufacturing of concrete is built. The primary purpose is measuring and monitoring the properties of amortar during the printing process.The following study investigates an approach for calculating yield stress and plastic viscosity based onexperimentally recorded pressure data. The calculations assume that fresh mortar behaves as a Bing-ham fluid and that the Buckingham-Reiner-equation is applicable. A test setup consisting of rigid pipeswith integrated pressure sensors at different positions is utilized.Monitoring the printing process with different sensors is crucial for the quality control of an ongoingprocess.
Bei der Betonage von Abdichtbauwerken können Temperaturen bis 110 °C und hohe Drücke bis 5 MPa erreicht werden. Mittels Technikumsversuchen wurde nachgewiesen, dass Mikroakustik- und Ultraschallsensoren zum Einbau in Demonstrationsbauwerke geeignet sind.
Die Untersuchungen wurden bei der BAM (Bundesanstalt für Materialforschung und -prüfung) in Berlin durchgeführt. Es ist vorgesehen, die Sensoren in Morsleben am Demonstrationsbauwerk im Anhydrit einzusetzen.
Ultrasonic echo testing is a well-established non-destructive testing technique used to investigate the interior of concrete structures in civil engineering. For the reconstruction of internal features, methods similar to seismic imaging are applied. To improve the ultrasonic imaging capabilities, we investigate the potential of a newly available 3D matrix mode measurement device in combination with advanced imaging techniques.
Commonly used ultrasonic array measurement devices rely on several ultrasonic transducers coupled to act as one transducer that transmits or receives transversal ultrasound waves. Although this approach is well suited to detect elongated structures such as pipes and rebars, it has limitations if 3D embedded objects are present. Hence, the ultrasonic device MiraA1040Pro used here is designed to measure the ultrasonic wavefield on a 4 by 16 matrix of individual transducers. For testing, we used laboratory specimens with linear and spheric embedded structures first. Both linear and matrix mode measurements were conducted and analysed using the Synthetic Aperture Focusing Technique
(SAFT) which is similar to Kirchhoff migration. Second, we used a data set from Teutschenthal mine at a shotcrete specimen constructed to simulate engineered barriers tailored for nuclear waste repositories. Ultrasonic measurements were investigated as a tool for quality assurance of these structures. The specimen contains both artificial 3D artifacts as well as naturally occurring defects such as a delamination. To make use of the advanced data acquisition, focusing 3D imaging techniques are applied to further improve the imaging quality.
Generally, the reconstructed images from the 3D matrix mode data have a lower level of Signal-to-Noise-Ratio than the 2D linear mode because the source signal is weaker compared to the linear mode. Moreover, complex wave conversions of the SH-transversal wave occur that are reduced in the 2D linear scenario. However, clearer images can be achieved at non-linear features, particularly with focusing imaging methods. Thus, combining 3D data acquisition techniques with advanced imaging methods improves the success in imaging complex concrete structures. This is of particular interest for thick concrete structures in nuclear barrier systems or foundations. Additionally, we demonstrate opportunities to use well-constrained test laboratory scenarios from non-destructive testing as a practical test case for geophysical methods.
Machbarkeitsstudie zur Zustandserfassung von Spannbetonschwellen mit dem Ultraschallverfahren
(2024)
Das niederfrequente Ultraschallverfahren zur zerstörungsfreien Zustandserfassung von Stahlbetonkomponenten findet im Bauwesen umfangreiche Anwendung. Multistatische Arrays sind am Markt verfügbar und ausgelegt für die Prüfung großflächiger Betonstrukturen. In einer Machbarkeitsstudie wird überprüft, ob eine Zustandserfassung an schlanken Spannbetonschwellen möglich ist. B70-Schwellen und B90-Weichenschwellen wurden hierfür im Labor, im Schienennetz und während der Wiederaufbereitung mit dem Ultraschallverfahren untersucht. Fokus ist die Detektion von Sickenrisse, Kopfrissen und Treibrissen im Bereich des Schwellenkopfes.
Die rekonstruierten Ultraschalldaten zeigen für intakt-klassifizierte Schwellen ein reproduzierbares Rückwandecho und weitere Reflexionen an den Schwellenaußenkanten. Die Ausprägung der Amplitude variiert je nach Degradation durch Belastung und Verwitterung. Defekt-klassifizierte Schwellen mit z. B. Kopfrissen oder unterseitigen Abplatzungen unterscheiden sich im Signalbild deutlich durch oberflächennahe Reflexionen bzw. verschobene Rückwandechos. Basierend auf den untersuchten Schwellen zeigt die Machbarkeitsstudie, dass eine zerstörungsfreie Zustandserfassung mit Hilfe des Ultraschallverfahrens grundsätzlich möglich ist.
Entwicklung einer flexiblen Datenablage zur sicheren Speicherung von Bauwerksdaten - "CASPAR"
(2024)
Bestandsunterlagen von älteren Bauwerken sind bezüglich einer rechnerischen Zustandsbewertung häufig nur in einem unzureichenden Umfang verfügbar. Dies gilt sowohl für den privaten als auch für den öffentlichen Bereich. Der Wert von Bestandsunterlagen für Gebäude oder Brücken ist Vielen nicht bekannt. Soll jedoch der aktuelle Zustand von Bauwerken bewertet, sollen Restlebensdauern abgeschätzt oder soll umgebaut werden, stellen Bestandsunterlagen die Grundlage dafür dar. Liegen diese nicht vor, so muss die Bauweise des Bauwerkes kostenintensiv nachvollzogen und mit nachträglichen Untersuchungsverfahren bewertet werden. Vor allem ist dies darauf zurückzuführen, dass die Aufbewahrung der Bestandsunterlagen dem Bauherrn obliegt und diese meist in Papierform vorliegen und dann bei Umzügen, Betriebsschließungen, Eigentümerwechsel etc. verloren gehen.
Die Digitalisierung im Bauwesen bietet hier Möglichkeiten diese Probleme künftig zu vermeiden. Bereits heute nimmt die digitale Planung im Bauwesen eine immer größere Rolle ein. Mehr und mehr Bauvorhaben werden schon jetzt in sogenannten BIM Modellen (Building Information Modelling) geplant. Um die Akzeptanz einer digitalen Lösung zu gewährleisten muss die Vertrauenswürdigkeit von Daten auch langfristig garantiert sein. Naturgemäß unterliegen Erkenntnisse, die aus Daten gewonnen werden, häufig vielen Prozessschritten mit unterschiedlichen Beteiligten. Es lässt sich vor dem Hintergrund der üblichen Lebensdauern von Bauwerken leicht erkennen, dass es schwierig ist diese Prozesskette, von der Datenerhebung bis zur teilweise jahrzehnte späteren Nutzung, beweissicher und rückführbar zu gestalten. Diese Attribute sind es aber, die die Vertrauensbasis für die Qualität und somit auch die Akzeptanz von digitalisierten Daten bilden. Im Projekt „CASPAR“ erarbeiten wir eine mögliche technologische Grundlage, um Bauwerksdaten langfristig und manipulationssicher zu speichern.