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Zusammenfassung
In der Geophysik wird seit einiger Zeit das Verfahren der "Spektralen Induzierten Polarisation (SIP)"eingesetzt, um nähere Informationen über die Art, die Struktur und den Zustand des Bodens zu erhalten. Die Methode beruht auf der Messung des komplexen spezifischen elektrischen Widerstands im Frequenzbereich zwischen 1 mHz und 10 kHz.
Die SIP kann neue Möglichkeiten beim Einsatz elektrischer Verfahren in der Bauwerksuntersuchung eröffnen. So lassen sich beispielsweise Materialunterschiede von Feuchteinhomogenitäten trennen, was mit konventioneller Widerstandsmessung nicht möglich ist. Ebenfalls denkbar ist eine Detektion kontaminierter Bereiche (z. B. bei starker Belastung durch organische Substanzen oder Salze) im Mauerwerk.
Vorgestellt werden das Verfahrensprinzip, die Messtechnik und erste Ergebnisse von Messungen an Mauerwerksziegeln.
The duraBASt area at the highway intersection “Köln-Ost” is a large test field for road testing.
It includes the duraBASt test bridge which is approximately 66 m long and 14.25 m broad. This bridge is part of the “road in the 21st Century” project and is equipped with several sensors for structural health monitoring. This feasibility study is carried out to investigate the prerequisites necessary for the constraction of intelligent bridges in the foture. Embedded sensors are able to measure quantities such as temperature, strain, moisture, corrosion, etc. In the presented work, the focus is set on passive RFID-based sensors. The communication and energy supply are realised by a mobile transmitter through the concrete cover. Hence, no cables or batteries are required. The sensors are designed to withstand the alkaline environment in concrete. Thus, moisture and corrosion values are measurable for several decades.
Spectral Induced Polarization - a Tool for Non-Destructive Testing of Soils and Building Materials
(2003)
The Spectral Induced Polarization (SIP) is a newly developed non-destructive geophysical method. It is an extension of conventional electrical resistivity measurements. By measuring additional parameters a more detailed investigation of the subsurface is possible. Up to now SIP is mainly used in mineral exploration, but the number of application examples from near surface geophysics and civil engineering is increasing. Results are presented from the investigation of slag heaps and measurements on bricks.
Spectral Induced Polarization - a Tool for Non-Destructive Testing of Soils and Building Materials
(2003)
Ultrasonic methods are well established in various aspects of concrete testing. They are used for imaging the interior geometry of constructions, estimation of concrete strength or monitoring lab investigations. However, so far the detection of distributed damages, especially in an early stage, has been almost impossible. The arrival of new technologies as deep penetration ultrasonic echo devices, new imaging techniques, embedded transducers for permanent monitoring and sensitive data processing techniques adopted from seismology have opened new fields of work. Recent research has been focused to detect changes in concrete elements induced by stress, temperature, moisture or chemical attacks.
Ultrasonic methods are well established in various aspects of concrete testing. They are used for imaging the interior geometry of constructions, estimation of concrete strength or monitoring lab investigations. However, so far the detection of distributed damages, especially in an early stage, has been almost impossible. The arrival of new technologies as embedded transducers and sensitive data processing techniques adopted from seismology has opened new field of work. Recent research has been focused to detect changes in concrete elements induced by stress, temperature, moisture or chemical attacks by permanent monitoring. Techniques as Coda Wave Interferometry can resolve changes in ultrasonic velocity in the order of 1*10-5. In addition, many researchers believe that the investigation of nonlinear effects can be used to characterize damages.
The workshop will give a wrap up of ultrasonic techniques currently used in practice. This will include echo based methods as multi-channel/multi-offset imaging of structural elements using commercial and prototype devices. Imaging methods as SAFT and RTM will be shortly discussed.
The focus will be on the emerging techniques used for monitoring. New types of sensors will be presented as well as the devices used in laboratory and field applications. Insight will be given on the various influence factors on ultrasonic signals and various ways of feature extraction and data processing. The results of lab experiments will be shown to demonstrate the detection of various kind of damages from mechanical load, ASR, corrosion to fatigue. The experiences with or first installations in real constructions (bridges, tunnel) will also be presented.
Ultrasonic methods are well established in various aspects of concrete testing. They are used for imaging the interior geometry of constructions, estimation of concrete strength or monitoring lab investigations. However, so far the detection of distributed damages, especially in an early stage, has been almost impossible. The arrival of new technologies as embedded transducers and sensitive data processing techniques adopted from seismology has opened new field of work. Recent research has been focused to detect changes in concrete elements induced by stress, temperature, moisture or chemical attacks by permanent monitoring. Techniques as Coda Wave Interferometry can resolve changes in ultrasonic velocity in the order of 1*10-5. In addition, many researchers believe that the investigation of nonlinear effects can be used to characterize damages. The presentation will give a wrap up of ultrasonic techniques currently used in practice. This will include echo based methods as multi-channel/multi-offset imaging of structural elements using commercial and prototype devices. Imaging methods as SAFT and RTM will be shortly discussed. The focus will be on the emerging techniques used for monitoring. New types of sensors will be presented as well as the devices used in laboratory and field applications. Insight will be given on the various influence factors on ultrasonic signals and various ways of feature extraction and data processing. The results of lab experiments will be shown to demonstrate the detection of various kind of damages from mechanical load, ASR, corrosion to fatigue. The experiences with or first installations in real constructions (bridges, tunnel) will also be presented.
Static and dynamic pile tests are carried out to determine the load bearing capacity and the quality of reinforced concrete piles. As part of a round robin test to evaluate dynamic load tests, structure integrated fibre optic strain sensors were used to receive more detailed information about the strains along the pile length compared to conventional measurements at the pile head. This paper shows the instrumentation of the pile with extrinsic Fabry-Perot interferometers sensors and fibre Bragg gratings sensors together with the results of the conducted static load test as well as the dynamic load Tests and pile integrity tests.
Tailings are the fine residue of the milling process in the mining industry and appear in slurry form being mixed with water during this process. Large tailings ponds are required to contain them, usually confined by man-made dams. Such tailings facilities pose considerable risk both to the environment and human lives.
A major interdisciplinary research project ('TAILSAFE') supported by European Union has been initiated with the aim to increase attention towards and reduce the risk posed by tailings facilities. Methods of parameter evaluation and measurement are being developed within the project and applied for the detection, assessment and improvement of the safety state of tailings dams and ponds.
One of the workpackages has his focus on non-destructive geophysical investigation methods. Geoelectrical (SIP), seismic and radar methods will be used to get information on the tailings dam structure and water content.
Improperly built or managed tailing dams pose major risks to human lives and the environment. Research for risk reduction by new technologies including slurry handlings, stochastic modelling, development of a parameter framework as well as work on legislation and authorisation procedures will be done in the EC-funded project TAILSAFE. Focus of this paper is on geophysial techniques for structure investigation and monitoring.
The process of ensuring reliability of NDT applications contains various aspects, such as determining the performance and probability of success, the uncertainty in measurement, the provision of clear and functional procedures and ensuring the correct application accordingly. Test specimens have become powerful elements in supporting many of these aspects. Within the committee for NDT in Civil Engineering (NDT-CE) of the German Society for Nondestructive Testing (DGZfP), the subcommittee on Quality Assurance (UA-QS) therefore addresses the design and the integration of test specimens in the quality assurance process. Depending on the specific purpose, the requirements on test specimens can vary significantly based on the defined simulated scenario. The most prominent purposes of test specimens might be seen in providing references for inspection systems in regard to function control, calibration and validation. Further aspects can be parametric studies, basic investigation of physical principles related to NDT or a simplified and therefore comprehensive demonstration of inspection concepts (e.g. for teaching purposes). The specific purpose of a test specimen dictates the requirements regarding its conception, including the exact design, the material or the fabrication accuracy and the conditioning. In the development of a general guideline by the UA-QS for application-specific procedures and their validation, the use of test specimens is addressed and specific concepts for the design of test specimens are made. This includes the analysis of the measurement process regarding any given application, deriving an adequate calibration approach for it and designing test specimens (calibration specimens) accordingly. Furthermore, it includes the validation of the procedure taking into account all conditions related to the specific application in the field. The validation requires a statistically sufficient number of trials. Thorough evaluation of each trial can only be established if the ground-truth is known. Therefore, test specimens providing a realistic but controlled simulation of the inspection problem are valuable and indispensable elements in the validation process. The requirement of being fully realistic will often not be possible to fulfill due to practical restrictions. Any aspect that cannot be included in the simulation realistically needs to be simulated conservatively. This again, requires a sufficient understanding of the inspection principle and technique to ensure conservativeness. Among other quality-assurance-related aspects, the UA-QS establishes concepts and guidelines regarding sound and efficient approaches for the specific purposes of test specimens. This subcommittee brings together representatives of different Groups along the entire value chain of NDT-CE, including researchers, practitioners, manufacturers and clients. They all work together in establishing a common understanding and level of quality assurance in the industry.
This article presents a unique method of installing a special type of embedded ultrasonic transducers inside a 36-m-long section of an old bridge in Germany. A small-scale load test was carried out by a 16 ton truck to study the temperature and load influence on the bridge, as well as the performance of the embedded transducers. Ultrasonic coda wave interferometry technique, which has high sensitivity in detecting subtle changes in a heterogeneous medium, was used for the data evaluation and interpretation. The separation of two main influence factors (load effect and temperature variation) is studied, and future applications of wave velocity variation rate Φ for structural health condition estimation are discussed. As a preliminary research stage, the installation method and the performance of the ultrasonic transducer are recognized. Load- and temperature-induced weak wave velocity variations are successfully detected with a high resolution of 10−4%. The feasibility of the whole system for long-term structural health monitoring is considered, and further research is planned.
The LAUS: First Applications of a New System for Ultrasonic Imaging of Very Concrete Structures
(2019)
The LAUS (Large Aperture Ultrasonic System) has been developed to image very thick concrete structures, which are not accessible for commercial systems. The device and the corresponding software is the result of joint Research of BAM, an ultrasonic instrument manufacturer and University of Kassel, Germany. It consists of 12 separate Arrays of 32 point-contact shear wave transducers each, which can be deployed in flexible configurations. Each array is combined with battery and transmitter, receiver and wireless communication electronics.
Three case histories are presented. First the system was deployed on a 5-m thick heavily reinforced foundation slab.
The reflection of the slab’s bottom was imaged clearly. In addition, a multiple reflection was registered, thus giving hope that even thicker elements might be imaged by the instrument. Second, the LAUS was used to investigate a massive bridge girder where a heavy rainstorm during concreting had led to imperfections that were visible after removing the formwork was removed. The LAUS could image tendon ducts in 1.8m depth and the backwall closely behind them. Some limited areas showed blurred reflections and were checked by drill holes; these areas were affected by diffuse damage which could be repaired by injections. Third, a large retaining wall was checked for thickness.
Meanwhile, the LAUS has been used in underground waste deposits (nuclear and other) for quality assurance of sealing plugs. A confirmed penetration depth of about 7 m has been reached.
The LAUS: First applications of a new system for ultrasonic imaging of very concrete structures
(2018)
The LAUS (Large Aperture Ultrasonic System) has been developed to image very thick concrete structures, which are not accessible for commercial systems. The device and the corresponding software is the result of joint research of BAM, an ultrasonic instrument manufacturer and University of Kassel, Germany. It consists of 12 separate arrays of 32 point-contact shear wave transducers each, which can be deployed in flexible configurations. Each array is combined with battery and transmitter, receiver and wireless communication electronics.
Three case histories are presented. First the system was deployed on a 5-m thick heavily reinforced foundation slab. The reflection of the slab’s bottom was imaged clearly. In addition, a multiple reflection was registered, thus giving hope that even thicker elements might be imaged by the instrument. Second, the LAUS was used to investigate a massive bridge girder where a heavy rainstorm during concreting had led to imperfections that were visible after removing the formwork was removed. The LAUS could image tendon ducts in 1.8m depth and the backwall closely behind them. Some limited areas showed blurred reflections and were checked by drill holes; these areas were affected by diffuse damage which could be repaired by injections. Third, a large retaining wall was checked for thickness.
Meanwhile, the LAUS has been used in underground waste deposits (nuclear and other) for quality assurance of sealing plugs. A confirmed penetration depth of about 7 m has been reached.
The parallel seismic method for foundation length measurement: useful also to check pile integrity?
(2012)
The parallel seismic method for foundation length measurement: Useful also to check pile integrity?
(2012)
To provide better means for a safe and effective monitoring of cemented waste packages including prediction tools to assess the future integrity development during pre-disposal activities, several digital tools are evaluated and improved in the frame of the EC funded project PREDIS. Safety enhancement (e. g. less exposure of testing personnel) and cost effectiveness are part of the intended impact.
The work includes but is not limited to inspection methods such as muon imaging, wireless sensors integrated into waste packages as well as external package and facility monitoring such as remote fiber optical sensors. The sensors applied will go beyond radiation monitoring and include Proxy parameters important for long term integrity assessment (e. g. internal pressure). Sensors will also be made cost effective to allow the installation of much more sensors compared to current practice.
The measured data will be used in digital twins of the packages for specific simulations (geochemical, integrity) providing a prediction of future behavior. Machine Learning techniques trained by the characterization of older packages will help to connect the models to the actual data.
All data (measured and simulated) will be collected in a joint data base and connected to a decision framework to be used at actual facilities.
The presentation includes detailed information about the various tools under consideration, their connection and first results of our research.
The workpackage 7 of the EC funded project PREDIS deals with cemented low and intermediate level radioactive waste. The focus is on NDT/monitoring technologies, digiutal twins and data/decision frameworks to optimize facilitay and waste package management. The talk describes the project setup and planned activities.
Due to the importance of reinforced concrete structures for modern society, damage assessment during the entire life-cycle of such structures has become a special interest in non-destructive testing. Using embedded ultrasound sensors in combination with other measurement methods, numerical modeling and self-made data collectors, tailored specifically for monitoring tasks, the German research group DFG FOR CoDA aims to investigate and develop novel methods for damage detection and rapid model updating in reinforced concrete structures. In the first stage of the project, besides the development of custom-built, low-cost data collectors, ultrasonic transducers are embedded in a large, reinforced concrete specimen on a BAM test site near Berlin. In this experiment, the influence of changing environmental conditions (mainly temperature) on the ultrasound signal is investigated using coda-wave interferometry. The results show a correlation between changes in temperature and ultrasonic velocity. Such changes must be taken into consideration in a long-term monitoring setup to distinguish between reversible and permanent changes. By correcting the data using a linear relation between concrete temperature and velocity change to remove the seasonal trends and by low-pass filtering the data to remove daily variations can remove most of the temperature influence on the ultrasound measurements.
Parallel Seismic was introduced about four decades ago for foundation length estimation. As the borehole required by this test is in most cases more expensive than the test itself, the usage is limited so far. In addition the graphical Interpretation technique which is still state of the art tends to overestimate the length and neglects several geometrical Parameters. New Interpretation algorithms have been recently introduced rely on model based travel time curve Utting. They improve the accuracy and extend the maximum ränge (distance pile to borehole) of the method. Borehole or pile inclination as well as soil layering can be considered. If the location is properly chosen, several piles can be tested using a single borehole.
The capabilities and limitations of the methods have been tested using simulations and measurements at the BAM-TTS test site in Horstwalde south of Berlin and several commercial projects involving piles, pile secant walls and sheet piles. To improve the accuracy of the method as well as to provide additional Parameters to the geotechnical engineer it is recommended to use the borehole for Downhole Seismic measurements. Determination of compressional and shear wave velocities can be used to determine the dynamic elastic properties of the subsoil. The approach is evaluated again on the BAM-TTS test site. The affectivity of this kind of combiuation can be further enhanced by using a seismic cone.
Die Überwachung von Bauteilen aus Stahl- oder Spannbeton mit Ultraschall hat in Labor- und Technikumsversuchen schon vielversprechende Ergebnisse gezeigt. Besonders gute Resultate wurden dabei mit eingebetteten Ultraschalltrans-ducern und bei Auswertung der Daten mit der hochsensiblen Codawelleninterferometrie erzielt. Erfasst werden können neben Temperatur- und Feuchteeffekten auch Belastungszustände und jegliche Art von Schädigung, die mit Mikro- oder Makrorissbildung einhergeht.
Seit 2019 untersucht die DFG-Forschergruppe 2825 „CoDA“ (Sprecher: Prof. Christoph Gehlen, TU München) ver-schiedenste Aspekte dieser innovativen Technologie mit dem Ziel, Einflussgrößen quantitativ zu erfassen, Umweltein-flüsse zu korrigieren und 3D-Auswerteverfahren zu verbessern. Final soll eine am Bauwerk einsatzfähige Methode ent-stehen, die klassische Monitoringverfahren ergänzt und erweitert sowie Input zu einem Update des statischen Systems liefert.
Aufgaben der BAM in der Forschergruppe ist neben Verbesserung und Adaptierung der Messsystem und Sensorik auch Langzeitversuche an einem Großobjekt und Testinstallationen an Realbauwerken. Hierzu liegen erste Ergebnisse vor, die zeigen, dass die Technologie auch außerhalb des Labors einsatzfähig ist.
Die Überwachung von Bauteilen aus Stahl- oder Spannbeton mit Ultraschall hat in Labor- und Technikumsversuchen schon vielversprechende Ergebnisse gezeigt. Besonders gute Resultate wurden dabei mit eingebetteten Ultraschalltrans-ducern und bei Auswertung der Daten mit der hochsensiblen Codawelleninterferometrie erzielt. Erfasst werden können neben Temperatur- und Feuchteeffekten auch Belastungszustände und jegliche Art von Schädigung, die mit Mikro- oder Makrorissbildung einhergeht.
Seit 2019 untersucht die DFG-Forschergruppe 2825 „CoDA“ (Sprecher: Prof. Christoph Gehlen, TU München) ver-schiedenste Aspekte dieser innovativen Technologie mit dem Ziel, Einflussgrößen quantitativ zu erfassen, Umweltein-flüsse zu korrigieren und 3D-Auswerteverfahren zu verbessern. Final soll eine am Bauwerk einsatzfähige Methode ent-stehen, die klassische Monitoringverfahren ergänzt und erweitert sowie Input zu einem Update des statischen Systems liefert.
Aufgaben der BAM in der Forschergruppe ist neben Verbesserung und Adaptierung der Messsystem und Sensorik auch Langzeitversuche an einem Großobjekt und Testinstallationen an Realbauwerken. Hierzu liegen erste Ergebnisse vor, die zeigen, dass die Technologie auch außerhalb des Labors einsatzfähig ist.
Zu jedem Endlager gehört die Entwicklung eines Verschlusskonzept. Im Endlager Morsleben und an anderer Stelle werden in Abhängigkeit vom Wirtsgestein verschiedene Materialien und Bauweisen für Streckenverschlüsse entwickelt und in großem Maßstab erprobt. Hierzu gehören auch Maßnahmen der Qualitätssicherung, die Informationen über Ausführung und Zustand der Versuchsbauwerke liefern. Hierzu werden von der Bundesanstalt für Materialforschung und -prüfung (BAM) für verschiedene Forschungsvorhaben und Prüfaufträge Methoden und Geräte getestet, verbessert und vor Ort unter Tage eingesetzt Die hier beschriebenen Verfahren lassen sich auch zu Untersuchungen im Wirtsgestein anwenden.
Zu jedem Endlager gehört die Entwicklung eines Verschlusskonzept. Im Endlager Morsleben und an anderer Stelle werden in Abhängigkeit vom Wirtsgestein verschiedene Materialien und Bauweisen für Streckenverschlüsse entwickelt und in großem Maßstab erprobt. Hierzu gehören auch Maßnahmen der Qualitätssicherung, die Informationen über Ausführung und Zustand der Versuchsbauwerke liefern. Hierzu werden von der Bundesanstalt für Materialforschung und -prüfung (BAM) für verschiedene Forschungsvorhaben und Prüfaufträge Methoden und Geräte getestet, verbessert und vor Ort unter Tage eingesetzt. Die hier beschriebenen Verfahren lassen sich auch zu Untersuchungen im Wirtsgestein anwenden.
Ultrasonic monitoring, making use of the sensitivity of the coda of repeated transmission meas-urements to changes in stress, temperature, moisture, as well as localized or distributed damage, has gotten at-tention in structural health monitoring (SHM) research recently. Analysis methods such as coda wave inter-ferometry (CWI), including its nonlinear extension, have been shown to be able to measure ultrasonic wave velocity changes with a 1∙10-5 resolution, while indicators such as cross-correlation or cross-coherence have been used to distinguish between reversible and irreversible changes. Several small- and large-scale laboratory experiments have demonstrated that stress changes in structures can be captured or damage detected in a very early stage. The use of this technique for pre-warning before failure are currently under investigation, as well as detailed research on the physical causes and the connection between ultrasonic wave properties and materi-al/structural behavior. Recently, several of large-scale laboratory and real structures have been instrumented with embedded ultrasonic transducers to gather experience and evidence on how to use this technology in re-al-world applications. Preliminary results from installations on a new bridge, an existing bridge, a tunnel, a la-boratory earthquake test as well as a historic stadium in Germany, Poland, and the United States, respectively, are presented. Environmental influences (mainly temperature) and validation by load tests are discussed.
Ultrasonic monitoring, making use of the sensitivity of the coda of repeated transmission meas-urements to changes in stress, temperature, moisture, as well as localized or distributed damage, has gotten at-tention in structural health monitoring (SHM) research recently. Analysis methods such as coda wave inter-ferometry (CWI), including its nonlinear extension, have been shown to be able to measure ultrasonic wave velocity changes with a 1∙10-5 resolution, while indicators such as cross-correlation or cross-coherence have been used to distinguish between reversible and irreversible changes. Several small- and large-scale laboratory experiments have demonstrated that stress changes in structures can be captured or damage detected in a very early stage. The use of this technique for pre-warning before failure are currently under investigation, as well as detailed research on the physical causes and the connection between ultrasonic wave properties and materi-al/structural behavior. Recently, several of large-scale laboratory and real structures have been instrumented with embedded ultrasonic transducers to gather experience and evidence on how to use this technology in re-al-world applications. Preliminary results from installations on a new bridge, an existing bridge, a tunnel, a la-boratory earthquake test as well as a historic stadium in Germany, Poland, and the United States, respectively, are presented. Environmental influences (mainly temperature) and validation by load tests are discussed.
In the framework of non-destructive-testing advanced seismic imaging techniques have been applied to ultrasonic echo data in order to examine the integrity of an engineered test-barrier designed to be used for sealing an underground nuclear waste disposal site. Synthetic data as well as real multi-receiver ultrasonic data acquired at the test site were processed and imaged using Kirchhoff prestack depth migration reverse time migration (RTM). In general, both methods provide a good Image quality as demonstrated by various case studies, however deeper parts within the test barrier containing inclined reflectors were reconstructed more accurately by RTM. In particular, the image quality of a specific target reflector at a depth of 8 m in the test-barrier has been significantly improved compared to previous investigations using synthetic aperture Focusing technique, which justifies the considerable computing time of this method.
The structural integrity of sealing structures in underground repositories for radioactive waste is a major concern regarding safe disposal. Non-destructive testing plays a very important role in the safety of this sealing structures. Ultrasonic pulse echo technology has been established in the construction industry as a non-destructive testing method for locating potential defects and material characterization of concrete structures. A borehole probe is an ultrasonic pulse-echo device used to investigate the internal structures of salt concrete. A prototype borehole probe is successfully demonstrated with the existing research borehole in the test site using a commercially available flaw detector. A novel phased array borehole probe that allows the beam to be focused based on the delay law was constructed and tested. The directivity measurements on the semi-cylindrical concrete sample agree well with the simulation results for the different focusing angles. In combination with geophysical reconstruction methods, the optimized radiation pattern of the probe is expected to improve the signal quality and thus increase the reliability of the imaging results. In addition, a unique large aperture ultrasound system (LAUS) is expected to provide enhanced images of possible cracks and embedded objects in in-situ structures. LAUS will be optimized to reliably detect objects at depths greater than 9 m and, at the same time, provide good resolution. Modeling studies show the potential to increase the distance between the transducer arrays further, and the same configuration has been successfully tested on a thick concrete wall. Overall, the paper shows that quality assurance using ultrasonic testing is crucial for constructing safe sealing structures to dispose of radioactive or toxic waste.
Ultrasonic non-destructive testing methods have found various applications in quality assurance and condition assessment of nuclear concrete structures. This includes but is not limited to the localization of construction features (thickness measurements, reinforcement, tendon ducts, and others) and damage detection (e. g. corrosion or cracks). However, there are still limitations, e. g. limited penetration depth and resolution, issues when testing hybrid steel/concrete structures as well as absence of standards and regulations.
This presentation will show progress in some of these issues and will focus on advanced instrumentation and validation of ultrasonic NDT for concrete structures.
Ultrasonic echo testing has been limited to a penetration depth of less than one meter in reinforced concrete. The development of the LAUS (Large Aperture Ultrasonic System), using a large array of ultrasonic transducers and wider offsets between transmitter and receiver, allows to reach up to 5 m in reinforced concrete and 9 m in unreinforced concrete. This capability has been demonstrated by collecting data from an engineered salt concrete barrier in an underground nuclear waste storage facility. Due to an increasingly competitive environment, commercial manufacturers will continue to develop equipment with enhanced penetration and/or increased resolution.
To quantify the capabilities and reliability of ultrasonic tests, validation mockups with engineered flaws are required. EPRI and BAM have built a large-scale mockup at a test site close to Berlin (BAM-TTS, Horstwalde) using a design which is repeated at other places. This presentation will also cover the methods deployed on engineered flaws and the repeatability of the test results.
Ultrasonic transmission measurements are used to monitor concrete elements mostly on a laboratory scale since decades.
Recently, coda wave interferometry, a technique adapted from seismology, has been introduced to civil Engineering experiments. It can be used to reveal subtle changes in concrete samples and even large construction elements without having a transducer directly at the location where the change is taking place. The methodology works best with embedded transducers to avoid coupling issues or excessive environmental influence. These transducers can be used for newly built and existing structures. Recently, large concrete beams have been equipped with a network of transducers and loaded until failure. Using code wave interferometry, it was possible to visualize stress fields and damaged areas.
Previous work has shown that ultrasonic monitoring using externally applied or embedded transducers and imaging methods based on coda wave interferometry are able to detect subtle changes in concrete elements. In this study, a limited number of embedded transducers has been used to monitor changes in several 12 m long two-span concrete beams subjected to point or linear loads until failure.
The ultrasonic results showed the high sensitivity to stress changes and the nonlinear character of the associated effects. However, the ultrasonic features showed a very good correlation to several conventional monitoring parameters. For higher loads (significant amount of cracking), the technique had to be modified to cope with large wave velocity variations and high decorrelation compared to the reference signal.
Using a very simple imaging procedure, the 2D stress field inside the beam has been visualized including inhomogeneities and artifact at places where cracking occurred at higher loads. The technique has the potential to be included in real time monitoring systems.
Ultrasonic transmission measurements are used to monitor concrete elements mostly on a laboratory scale since decades. Recently, coda wave interferometry, a technique adapted from seismology, has been introduced to civil engineering experiments. It can be used to reveal subtle changes in concrete samples and even large construction elements without having a transducer directly at the location where the change is taking place. The methodology works best with embedded transducers to avoid coupling issues or excessive environmental influence. These transducers can be used for newly built and existing structures. Recently, large concrete beams have been equipped with a network of transducers and loaded until failure. Using code wave interferometry, it was possible to visualize stress fields and damaged areas. This paper gives an overview of the state of the art, recent results achieved at BAM and a task list for further results and development.
Ultrasonic transmission measurements are used to monitor concrete elements mostly on a laboratory scale since decades. Recently, coda wave interferometry, a technique adapted from seismology, has been introduced to civil engineering experiments. It can be used to reveal subtle changes in concrete samples and even large construction elements without having a transducer directly at the location where the change is taking place. The methodology works best with embedded transducers to avoid coupling issues or excessive environmental influence. These transducers can be used for newly built and existing structures. Recently, large concrete beams have been equipped with a network of transducers and loaded until failure. Using code wave interferometry, it was possible to visualize stress fields and damaged areas. This paper gives an overview of the state of the art, recent results achieved at BAM and a task list for further results and development.
Engineered barriers are a key element to enable safe nuclear waste disposal. One method currently under research for their construction is magnesia concrete applied in a shotcrete procedure. In this study, the ultrasonic echo method is evaluated as a means for quality assurance. Imaging of internal structures (backwall, boreholes) and defects, such as delamination, has successfully been achieved in the shotcrete. Additionally, detailed information about the potential cause of selected reflectors are obtained by phase analysis. In several test blocks of various sizes, no consistent concrete section boundaries have been found by ultrasonic imaging, which was verified by subsequent drilling and complementary tests. An experiment with artificial defects imitating cracks, air-filled voids, and material with lower density has been challenging and shows the limitations of the current methods. Although significant defects, such as a large delamination, are reliably identified, several smaller defects are not identified. Generally, ultrasonic imaging provides a suitable base as a mean for quality assurance during and after the construction of sealing structures. However, further developments are required to enhance the reliability of the method and a full validation is still pending. Still, the method has potential to increase the safety of nuclear waste repositories.
Underground sealing structures are necessary to seal radioactive or toxic waste in underground repositories. A special version of MgO concrete is used in the mine in Teutschenthal and applied at a large-scale test with the aim to provide a low permeability barrier. The test structures (up to 10 m long) were created by shotcreting. Besides destructive tests, non-destructive ultrasonic measurements have been evaluated for quality assurance to monitor potential anomalies such as cracks, concrete inhomogeneities, and delamination. We show results of ultrasonic measurements with a multi-transducer system used at the front and from the side of the concrete structure. Images are obtained by synthetic aperture focusing techniques. The boundaries between concreting sections are not visible in the ultrasonic images systematically so that a successful concreting is assumed, which is confirmed by the low permeabilities observed. Several reflectors up to a depth of 1.2 m are identified and interpreted as potential damages in the concrete. Phase analysis of prominent reflectors reveal a negative impedance contrast thus indicating air filled voids, cracks or delamination. Boreholes through some of the identified reflectors are used to verify the results from ultrasonic measurements. Additionally, an experiment with incorporated artificial defects was undertaken to analyse the reliability of the applied methods. Overall, the conducted tests show the potential of ultrasonic measurements to detect critical anomalies. Despite challenges at small-scale structures (cm-order), large-scale anomalies can be identified. Consequently, implementing ultrasonic monitoring during and after the construction of concrete sealing structures has shown its potential as a tool for quality assurance, but needs further development and validation.
At BAM a multi-sensor robot system BetoScan is used for the investigation of reinforced concrete floors affected by corrosion in parking garages.
Potential maps, as well as the distribution of concrete cover and moisture can be assessed simultaneously and data can be collected contactlessly. In order to evaluate the extent of degradation adequately and to divide the investigated structure into zones with defined damage classes, large data sets have to be collected and interpreted manually. Thus, to promote an efficient data evaluation framework, which could speed up and simplify the evaluation of large data sets, an unsupervised data fusion is of major interest. However, taking into account that collected data do not certainly coincide in space, a scattered data interpolation method should be applied prior data fusion.
In the paper, a case study involving a BetoScan data set acquired from a reinforced concrete floor of a parking garage in Germany is presented. The data set includes potential mapping, covermeter based on eddy current, as well as microwave moisture measurements. Among the examined methods for interpolation of scattered data, kriging shows to yield smooth interpolated data plots even in the case of very sparse data. In the post-processing step, the investigated structure is efficiently segmented into zones using clustering based data fusion methods, which prove to be robust enough also for handling noisy data. Based on the minimization of the XB validity index, an unsupervised selection of optimal segmentation into damage classes is derived.
Das Sorptionsverhalten und die Frost-Tau-Beständigkeit von Baustoffen hängen maßgeblich von ihrer Porengrößenverteilung ab. Ein zerstörungsfreies, räumlich visualisierendes Messverfahren, das diese
abschätzen könnte, wäre für die Bau- und Sanierungsindustrie sehr hilfreich. Scott und Barker (2003) berichteten über einen deutlichen Zusammenhang zwischen dominanter Porenhalsgröße und der SIP-Relaxationszeit an Sandsteinen. Diese Korrelation wird seit einiger Zeit für Baustoffe, insbesondere Sandsteine, an der BAM untersucht.
Die Coda transmittierter Ultraschallsignale in Beton enthält Informationen zu Struktur und Zustand des Materials bzw. deren Änderung. Relevant sind u. a. Temperatur, Stress, Feuchtigkeit und verschiedene Schädigungsmechanismen. Die zahlreichen Einflussfaktoren sind nur schwer zu trennen und die Messeffekte oft zu Beginn sehr klein.Die CWI ermöglicht die Detektion kleinster Geschwindigkeitsveränderungen durch den Vergleich, der in kleinen Schritten gestauchten oder gestreckten Signalen mit eine Referenzmessung. Andere Indikatoren für Änderungen im Material sind:
• Kreuzkorrelation
• Laufzeit direkte Welle
• Energie/Amplitude
• Änderungen im Frequenzspektrum
Die beschriebene Technik wird von uns bisher primär in klein- und großskaligen Laborversuchen genutzt. Die Forschung konzentriert sich auf die Untersuchung und Trennung verschiedener Einflusseffekte. Aber auch erste reale Bauwerke wurden schon instrumentiert, z. B. Brücken und eine Tunneldecke.
The re-use of foundations on urban sites contributes to the Sustainable Development in construction. Investigations at potential parts to be re-used should be performed in time to influence the planning process. Non-destructive testing methods in civil engineering (NDT-CE) provide necessary information about location, dimension and condition of existing foundations. Thickness measurement of foundation slabs, imaging of their geometry is dealt with as well as localisation of voids and reinforcement beyond surface-near layers. For pile foundations this article introduces NDT-CE methods to measure the pile length or deviation of an expected length as well as to determine the pile integrity. Practical examples of typical testing problems are given and show the possibilities as well as limits of a method. This guidance enables the planning engineer to consider the use of NDT-CE methods and to assure their successful application.
Moisture ingress is one of the major deteriorating factors for building materials. Today, the only approved way to assess such damage is the gravimetric Darr method, which is essentially destructive. Substantial progress has been made using the geophysical complex-resistivity method, which can be applied non-destructively and provides spatial information along two-dimensional sections, rather than punctual along one borehole. Considerable advantages of complex resistivity are its sensitivity to textural properties, as well as the pore-fluid chemistry of wet, porous media. In a comprehensive laboratory study, and later in field scale experiments, it could be shown that complex resistivity may even be able to distinguish between salt content and saturation degree in a single measurement. A comparison with complementary nondestructive testing techniques points to the benefit and further research to be explored in multimethodical approaches.
Challenging new constructions and ageing infrastructure are increasing the demand for permanent monitoring of loads and condition. Various methods and sensors are used for this purpose. But the technologies available today have difficulties in detecting slowly progressing locally confined damages. Extensive investigations or instrumentations are required so far for this purpose. In this study we present new sensors and data processing methods for ultrasonic transmission, which can be used for non-destructive long term monitoring of concrete. They can be mounted during construction or thereafter. Larger volumes can be monitored by a limited number of sensors for changes of material properties. The principles of ultrasonic transmission and influencing factors are presented. This latter include load, damages as well as environmental parameters as temperature or moisture. Various methods for data processing, e. g. coda wave interferometry are introduced. They allow the detection of very small changes in the medium. The embedded sensors are shown including mounting and operation. Application examples so far include small scale laboratory freeze-thaw experiments, localizing loads in larger concrete models, monitoring load effects on real structures as well as detecting acoustic events. Some sensors are operating already for several years. The sensors can be used as transmitter or receivers or switched between both roles. While most of the previous experiments have been active (at least one sensor serving as transmitter), new studies show that the sensors are useful as well for passive measurements, e. g. in acoustic emission or time reversal experiments. Besides application in civil engineering our setups can also be used for model studies in geosciences.
Modern geophysical methods might be either directly applied to concrete structures or integrated into existing testing schemes to assist in quality assurance and inspections. This paper gives an overview on some ideas and developments from the author’s work:
• Vibrator technologies to improve pile integrity testing.
• Ideas from vertical seismic profiling used in multichannel pile inspection
• Cross- and downhole seismics to check the diameter of jet grouting columns
• Improving the parallel seismic methods for precise length measurement of piles and foundation walls
• Seismic migration methods to improve ultrasonic imaging of foundation slabs
• Seismological tools to monitor subtle changes in concrete constructions
The authors strongly believe that the cooperation between geophysics and civil engineering, which is obviously becoming stronger and stronger, will lead to a large number of innovative approaches.
The corner echo is a well-known effect in ultrasonic testing, which allows detection of surface breaking cracks with predominantly perpendicular orientation to the surface as, for example, corrosion cracks in metal pipes or shafts. This echo is formed by two planes, the surface of the crack and the surface which the crack breaks. It can also be classified as a half-skip method, since a reflection of the pulse occurs on the backwall before the reflection at the defect takes place. In combination with the diffraction from the crack tip, the corner echo also allows crack sizing. As shown in this paper, the corner reflection can be used in civil engineering for nondestructive inspection of concrete. Commercially available low frequency ultrasonic arrays with dry point contact sources generate SH transversal waves with sufficient divergence of the sound field in order to detect corner reflections. Ultrasonic line-scans and area-scans were acquired with a linear array on flat concrete specimens, and the data were reconstructed by the Synthetic aperture focusing technique. If the angles and the area of reconstruction are chosen accordingly, the corner echo reflection can be distinguished from other ultrasonic information. The corner echo can thus be used as a method for deciding whether a crack is a partial-depth crack or a full-depth crack and thus for obtaining a statement about crack depth. This paper presents corresponding experimental results obtained on concrete specimens with artificial test defects and cracks induced under controlled conditions.
Validation of novel ultrasonic phased array borehole probe by using simulation and measurement
(2022)
Low-frequency ultrasonic testing is a well-established non-destructive testing (NDT) method in civil engineering for material characterization and the localization of cracks, reinforcing bars and delamination. A novel ultrasonic borehole probe is developed for in situ quality assurance of sealing structures in radioactive waste repositories using existing research boreholes. The aim is to examine the sealing structures made of salt concrete for any possible cracks and delamination and to localize built-in components. A prototype has been developed using 12 individual horizontal dry point contact (DPC) shear wave transducers separated by equidistant transmitter/receiver arrays. The probe is equipped with a commercially available portable ultrasonic flaw detector used in the NDT civil engineering industry. To increase the sound pressure generated, the number of transducers in the novel probe is increased to 32 transducers. In addition, the timed excitation of each transducer directs a focused beam of sound to a specific angle and distance based on the previously calculated delay time. This narrows the sensitivity of test volume and improves the signal-to-noise ratio of the received signals. In this paper, the newly designed phased array borehole probe is validated by beam computation in the CIVA software and experimental investigations on a half-cylindrical test specimen to investigate the directional characteristics. In combination with geophysical reconstruction methods, it is expected that an optimised radiation pattern of the probe will improve the signal quality and thus increase the reliability of the imaging results. This is an important consideration for the construction of safe sealing structures for the safe disposal of radioactive or toxic waste.
Im rahmen des themenfeldprojektes LEBEWIND wurden Vorversuche zur Ultraschallprüfung von Groutverbindungen an Offshore-Windenergieanlagen gemacht. Die Experimente mit kommerzieller Prüftechnik in Echo und Transmission durch die Stahlwandung hindurch bestätigten, dass diese Bauweise so nicht prüfbar ist.
X-rays without X-rays: Can muon tomography provide pictures from within concrete and other objects?
(2024)
Until the 1980s radiography was used to inspect civil structures in case of special demands and showed a much better resolution than other NDT techniques. However, due to safety concerns and cost issues, this method is almost never used anymore. Meanwhile, non-destructive techniques such as ultrasound or
radar have found regular, successful practical application but sometimes suffer from limited resolution and accuracy, imaging artefacts or restrictions in detecting certain features when applied to reinforced or prestressed concrete inspection.
Muon tomography has received much attention recently. Muons are particles generated naturally by cosmic rays in the upper atmosphere and pose no risk to humans. Novel detectors and tomographic imaging algorithms have opened new fields of application, mainly in the nuclear sector, but also in spectacular cases such as the Egyptian pyramids.
As a first step towards practical application in civil engineering and as a proof of concept we used an existing system to image the interior of a reference reinforced 600 kg concrete block. Even with a yet not optimized setup for this kind of investigation, the muon imaging results have been at least of similar quality compared to ultrasonic and radar imaging, potentially even better. Recently, the research was expanded to more realistic testing problems such as the detection of voids in certain structural elements. However, before practical implementation, more robust, mobile, and affordable detectors would be required as well as user-Friendly imaging and simulation software.
The talk also discusses other applications , such as volcanology, mining and geothermal exploration.
Until the 1980s radiography was used to inspect civil structures in case of special demands and showed a much better resolution than other NDT techniques. However, due to safety concerns and cost issues, this method is almost never used anymore. Meanwhile, non-destructive techniques such as ultrasound or
radar have found regular, successful practical application but sometimes suffer from limited resolution and accuracy, imaging artefacts or restrictions in detecting certain features when applied to reinforced or prestressed concrete inspection.
Muon tomography has received much attention recently. Muons are particles generated naturally by cosmic rays in the upper atmosphere and pose no risk to humans. Novel detectors and tomographic imaging algorithms have opened new fields of application, mainly in the nuclear sector, but also in spectacular cases such as the Egyptian pyramids.
As a first step towards practical application in civil engineering and as a proof of concept we used an existing system to image the interior of a reference reinforced 600 kg concrete block. Even with a yet not optimized setup for this kind of investigation, the muon imaging results have been at least of similar quality compared to ultrasonic and radar imaging, potentially even better. Recently, the research was expanded to more realistic testing problems such as the detection of voids in certain structural elements. However, before practical implementation, more robust, mobile, and affordable detectors would be required as well as user-Friendly imaging and simulation software.
Dieses erste Memorandum zur Lehre und Forschung an deutschsprachigen Hochschulen auf dem Gebiet der zerstörungsfreien Prüfung im Bauwesen gibt einen Überblick hinsichtlich der akademischen Ausbildung und zeigt mögliche Schwerpunkte vor allem in der Lehre auf. Diese Schwerpunkte berücksichtigen auch aktuelle Entwicklungen und Themen auf dem Gebiet der Forschung. Es werden Anregungen zur Entwicklung bzw. Weiterentwicklung der Lehr-Curricula im Hinblick auf eine umfassende und solide fachliche Ausbildung der Studierenden des Bauwesens und angrenzender Fachrichtungen gegeben. Inhaltlich und formal lehnt sich der Beitrag an dem Memorandum der Hochschullehrer im Fachgebiet „Werkstoffe im Bauwesen“ (Breit et al., 2012) an und beruht auf einer Initiative des Unterausschusses Ausbildung – Arbeitsgruppe Ausbildung in der Hochschule – des Fachausschusses ZfP im Bauwesen der Deutschen Gesellschaft für zerstörungsfreie Prüfung (DGZfP). Die Hauptredaktion wurde übernommen von Prof. Christian U. Grosse (TU München) und Prof. Ralf W. Arndt (FH Erfurt).
Der Vortrag behandelt den Stand der Technik bei der zerstörungsfreien Prüfung von Betonkonstruktionen und insbesondere den Stand und die Herausforderungen bei der Digitalisierung. Es werden Prüfaufgaben sowie etablierte Prüfmethoden und die passende Auswahl diskutiert. Ein weitere Schwerpunkt liegt bei der Genauigkeit und Verlässlichkeit und dem Konzept ZfPStatik. Abschließend werden Schnittstellen zu BIM, SIB-Bauwerke und anderen System kurz angerissen und ein Katalog offener Fragen aufgestellt.
Für die Qualitätssicherung von neuen Fundamenten steht eine Reihe von zerstörungsfreien Prüfverfahren zur Verfügung. Das Portfolio reicht von der einfachen Hammerschlagmethode („Pfahlintegritätsprüfung“) bis zu aufwändigen Ultraschallverfahren für meterstarke Fundamentplatten. Aber funktionieren die Verfahren auch im Bestand? Lassen sich die für Wieder-, Um- und Weiternutzung notwendigen Daten erfassen? Und wie werden die zerstörungsfreien Prüfverfahren erfolgreich in Untersuchungskonzepte integriert? Dies wird vor allem am Beispiel der Fundamente von Freileitungsmasten diskutiert.
Ein Ultraschallsystem mit großer Apertur, genannt LAUS – Large Aperture UltraSound, wird vorgestellt und die technischen Eigenschaften erläutert. Es besteht aus zwölf Prüfköpfen, die beliebig auf Betonoberflächen mit Unterdruck befestigt und jeweils als Sender oder Empfänger genutzt werden. Alle möglichen Kombinationen ergeben 132 Einzelmessungen, die zur Rekonstruktion des durchschallten Volumens genutzt werden. Das System wurde an zwei Bauwerken erfolgreich erprobt. Die Dicke einer sehr stark bewehrten Fundamentplatte eines Fallturms wurde bestimmt. Die Messungen erfolgten in einem Raster auf einer Fläche von 2,0 × 1,8 m2 und die Rückseite konnte eindeutig abgebildet werden. Weitere Anzeigen aus dem Inneren der Platte zeigen das Potenzial des Systems. An einem Brückenbauwerk wurden indirekt Verdichtungsmängel lokalisiert. Dazu wurden mit dem LAUS-System die im Brückenträger verlaufenden Spannkanäle durch fast 2 m Beton abgebildet.
Die ZfP ist im Bauwesen bisher deutlich weniger reguliert (und auch akzeptiert) als in anderen Industriebereichen. Zum Beispiel gibt für die meisten Prüfverfahren weder Normen noch ein allgemein akzeptiertes Ausbildungs- und Zertifizierungssystem.
Dies hat auch Konsequenzen für die Digitalisierung. Im Gegensatz dazu wird im Bauwesen derzeit für viele Bereiche verbindlich ein neues Verfahren zur Unterstützung von Design, Planung, Herstellung und Betrieb eingeführt: BIM (Building Information Modeling). Der Vortrag beleuchtet das Spannungsfeld zwischen dem geringen Organisations- und Standardisierungsgrad und den neuen digitalen Möglichkeiten und stellt den neuen Arbeitskreis zur ZfP 4.0 im Bauwesen vor. Er beleuchtet auch, in welchen Bereichen die ZfP im Bauwesen von Entwicklungen aus „Industrie 4.0“ und der zerstörungsfreien Prüfung in anderen Anwendungsbereichen profitieren kann - z. B. bei Datenformaten, Datenarchivierung und Schnittstellen.
Die ZfP ist im Bauwesen bisher deutlich weniger reguliert (und auch akzeptiert) als in anderen Industriebereichen. Zum Beispiel gibt für die meisten Prüfverfahren weder Normen noch ein allgemein akzeptiertes Ausbildungs- und Zertifizierungssystem.
Dies hat auch Konsequenzen für die Digitalisierung. Im Gegensatz dazu wird im Bauwesen derzeit für viele Bereiche verbindlich ein neues Verfahren zur Unterstützung von Design, Planung, Herstellung und Betrieb eingeführt: BIM (Building Information Modeling). Der Vortrag beleuchtet das Spannungsfeld zwischen dem geringen Organisations- und Standardisierungsgrad und den neuen digitalen Möglichkeiten und stellt den neuen Arbeitskreis zur ZfP 4.0 im Bauwesen vor. Er beleuchtet auch, in welchen Bereichen die ZfP im Bauwesen von Entwicklungen aus „Industrie 4.0“ und der zerstörungsfreien Prüfung in anderen Anwendungsbereichen profitieren kann - z. B. bei Datenformaten, Datenarchivierung und Schnittstellen.
ZfPBau-Kompendium 2004
(2007)
Dieses Kompendium ist ein kurzgefasster Abriss, ein Leitfaden und auch ein Handbuch der für den Einsatz im Bauwesen geeigneten zerstörungsfreien Prüfverfahren. In strenger, stets gleicher Gliederung wird jede der mehr als 100 Untersuchungsmethoden in einem eigenen Geräteblatt beschrieben. Hinzu kommen Querverweise zu alternativen Prüfmethoden sowie zahlreiche Hinweise auf einschlägige Fachliteratur und zu bekannt gewordenen Geräteherstellern, Lieferanten und Dienstleistern.
In this study, we use and extend a recently developed zonal cooperative inversion approach and apply it to the inversion of three independent geophysical field data sets. We invert crosshole P-wave, S-wave, and georadar data sets acquired in sand and gravel dominated unconsolidated sediments to detect and characterize different sedimentary units relevant for an engineering or hydrological site characterization. The zonal cooperative inversion of the three traveltime data sets results in a single subsurface model, which is a geophysical three-parameter model (P-wave, S-wave, and georadar velocity) outlining the major subsurface zonation while explaining all input data sets. Comparing our zonal model to direct push (DP) logging data (tip resistance, sleeve friction, and dielectric permittivity) shows good agreement; i.e., the zones in our geophysical model largely correspond to major DP parameter changes. Furthermore, we demonstrate how the sparse DP data can be inter- and extrapolated to the entire tomographic plane which allows for further geotechnical and hydrological interpretations. This study illustrates that the zonal cooperative inversion approach is highly flexible and an excellent tool to characterize a variety of environments in terms of multiple physical parameters.
Die B1 Brücke am Altstädter Bahnhof in Brandenburg an der Havel wurde im Dezember 2019 aufgrund von während einer turnusmäßigen Inspektion entdeckten Rissen und Hohlstellen entlang der vorgespannten Längsträger gesperrt und im Mai 2021 abgebrochen. In der Zwischenzeit wurde die Brücke detailliert überwacht. Vor dem Abriss wurden zudem umfangreiche Untersuchungen zur Bestandsaufnahme und Schadensanalyse sowie Tests moderner Sensorik vorgenommen. Dabei konnte sowohl die richtige, zuvor nicht sicher bekannte Anzahl von Spanngliedern in den Querträgern sicher ermittelt werden als auch durch moderne Varianten der Schwingungsmessungen und der faseroptischen Sensorik zusätzliche Kenntnisse püber das Bauwerksverhalten ermittelt werden . In dem Beitrag werden die Verfahren mit ihren Möglichkeiten und Grenzen vorgestellt, die Ergebnissee an der Brücke in Brandenburg erläutert und zukünftige Einsatzmöglichkeiten diskutiert.
Die B1 Brücke am Altstädter Bahnhof in Brandenburg an der Havel wurde im Dezember 2019 aufgrund von während einer turnusmäßigen Inspektion entdeckten Rissen und Hohlstellen entlang der vorgespannten Längsträger gesperrt und im Mai 2021 abgebrochen. In der Zwischenzeit wurde die Brücke detailliert überwacht. Vor dem Abriss wurden zudem umfangreiche Untersuchungen zur Bestandsaufnahme und Schadensanalyse sowie Tests moderner Sensorik vorgenommen. Dabei konnte sowohl die richtige, zuvor nicht sicher bekannte Anzahl von Spanngliedern in den Querträgern sicher ermittelt werden als auch durch moderne Varianten der Schwingungsmessungen und der faseroptischen Sensorik zusätzliche Kenntnisse püber das Bauwerksverhalten ermittelt werden . In dem Beitrag werden die Verfahren mit ihren Möglichkeiten und Grenzen vorgestellt, die Ergebnissee an der Brücke in Brandenburg erläutert und zukünftige Einsatzmöglichkeiten diskutiert.
Die immer komplexere Konstruktionsweise von Neubauten einerseits und die alternde Infrastruktur andererseits erfordern in manchen Fällen eine dauerhafte Überwachung, um besondere Einwirkungen und gegebenenfalls Schädigungen rechtzeitig und genau zu erkennen. Hierfür ist eine Vielzahl von Methoden und Sensoren verfügbar. Das Portfolio weist aber insbesondere bei der Detektion langsamer, räumlich begrenzter Veränderungen Lücken auf. Hierfür sind bisher sehr aufwändige Untersuchungen oder Installationen notwendig.
In der vorliegenden Arbeit werden Sensoren und zugehörige Auswertemethoden für die Ultraschalltransmission vorgestellt, die sich für die zerstörungsfreie, dauerhafte Überwachung von Beton eignen. Direkt oder nachträglich in Betonkonstruktionen eingebaut, ermöglichen sie eine nicht nur lokale, sondern größere Raumbereiche umfassende Dauerüberwachung von Änderungen der Materialeigenschaften.
Das Prinzip der Ultraschalltransmission und die verschiedenen Einflussparameter werden vorgestellt. Zu letzteren gehören neben der Belastung und Schädigung auch Umweltparameter wie Temperatur und Feuchte. Verschiedene Methoden zur Datenanalyse, wie z. B. die Codawelleninterferometrie, ermöglichen eine Detektion kleinster Veränderungen. Die in den Beton einzubettenden Ultraschallsensoren werden vorgestellt und ihr Einbau und Betrieb beschrieben. Als Beispiele für Anwendungen werden Frost-Tauwechsel-Experimente im Labor, die Detektion von lokalen Lasten im Technikumsmaßstab und der Einsatz an realen Brücken diskutiert. Die Sensoren sind zum Teil bereits seit mehreren Jahren in Probeobjekte eingebettet und liefern zuverlässig wertvolle Daten.-------------------------------------------------------------------------------------------------------------------------------------------------------------
Monitoring of concrete constructions by embedded ultrasonic sensors:
Challenging new constructions and the ageing infrastructure are increasing the demand for permanent monitoring of loads and damages. Various methods and sensors are used for this purpose. But the technologies available today have difficulties in detecting slowly progressing locally confined damages. Extensive investigations or instrumentations are required so far for this purpose.
In this study we present new sensors and data processing methods for ultrasonic transmission, which can be used for non-destructive permanent monitoring of concrete. They can be mounted during construction or thereafter. Larger volumes can be monitored by a limited number of sensors for changes of material properties.
The principles of ultrasonic transmission and influencing factors are presented. This latter include load, damages as well as environmental parameters as temperature or moisture. Various methods for data processing, e. g. coda wave interferometry are introduced. They allow the detection of very small changes in the medium. The embedded sensors are shown including mounting and operation. Application examples so far include small scale laboratory freeze-thaw experiments, localizing loads in larger concrete models and monitoring load effects on real structures. Some sensors are operating already for several years.