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Nuclear Power Plants have been in operation for ca. 50 years. Based on this experience, non-destructive testing tasks specific to thick and highly reinforced nuclear containment structures have materialized. The performance based Service life extension of existing NPPs also needs a measurement based decision to support continuing the service of the concrete part of the installations.
By nature, concrete is a very durable material and any natural Deterioration processes may take a long time to become critical to the structure. The experience of more than 50 years of service limits the testing tasks to a few ones which are not yet solved.
Research in NDT of concrete structures is performed by many research institutions all over the world with different technical and systematic approaches. Results are mainly obtained on laboratory specimens, sometimes additional field studies are reported. This research takes place independently without coordination and as a result, the outcomes mostly lack full comparability.
Software for data analysis has become indispensable and very powerful. This part of testing needs more attention when it comes to evaluate test results. Validation of NDE solutions is becoming a critical part in concrete structure testing.
Validation is by definition the proof that a customer´s requirements in the test are being met by the testing solution. This includes equipment, personnel qualification and data analysis. In the following tables, the research recommendation Validation is used in the sense, that proof of the performance of existing solutions needs to be adressed. In general, a validation methodology for NDE solutions for concrete testing in itself needs to be researched and established.
Comparability of research also needs an accepted and easily accessible reference. From experience, it is almost impossible to manufacture exact copies of test specimens at different locations. Round Robin tests are therefore needed to evaluate the performance of a test.
Data evaluation is generally done using dedicated software, sometimes Hardware dependant and not interchangeable between systems. Software is ever more increasingly becoming more powerful and sophisticated. An in-depth evaluation needs to address the comparability and validation of Software used for data analysis and evaluation. The vision of a unified software pool for NDE investigations would undoubtedly support research tremendously.
Quantitative NDE is mostly recommended to assess the condition of a structure. However, qualitative data can be very useful, especially for processes which change the material properties or deteriorate the structure (e.g. corrosion of reinforcement). The need for reliable baseline data is a key factor for such monitoring tasks.
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.
Research and Development in Non-Destructive Testing in Civil Engineering at BAM has de-veloped over more than two decades. Highlights of present research are ultrasound phase array probes, ground penetrating radar applications for the assessment of existing structures and Laser Induced Breakdown Spec-troscopy (LIBS) to determine which chemical elements on the surface of a specimen are. RFID sensor devel-opments for wireless moisture monitoring and data fusion for the combined analysis of sensor data are fast developing areas. In addition, a selection of application cases is briefly described.
Vortrag über die Aktivitäten des Fachbereichs 8.2 in der zerstörungsfreien Prüfung im Bauwesen.
The presentation is #4 of the lecture series within the CE5390 NDT&E Course at the “University of Texas at El Paso”, USA (UTEP):
1. Application of NDT to Transportation Infrastructure
2. Application of NDT to Pavements
3. Application of NDT to Tunnels
4. Application of NDT to Nuclear Structures
5. Ultrasonic Methods
6. Electrical Resistivity (ER)
7. Galvanostatic Pulse Measurement (GPM)
8. Half-Cell Potential (HCP)
9. Ground Penetrating Radar (GPR) to Infrastructure
10. Ground Penetrating Radar (GPR) to Pavements
11. Impact Echo (IE)/Ultrasonic Surface Waves (USW)
12. Infrared Thermography (IR)
13. Magnetic Flux Leakage (MFL)
14. Ultrasonic Tomography (UST)
15. Falling Weight Deflectometer/Light Weight Deflectometer
16. Spectral Analysis of Surface Wave
17. Traffic Speed Deflectometer
18. Integrity of Foundations
19. Integration of Technologies
Applications of NDT for nuclear structures are presented with an overview over the special challenges for NDE in this area.
The lecture was held as a webinar on August 29, 2017
Non-Destructive assessment of the National Infrastructure in Germany has been the topic of R&D at BAM since many years. In 1989 BAM has established a R&D group dedicated to the development and application of Non-Destructive Testing in Civil Engineering. Since then, this group has left has participated in numerous research projects and cooperated with many researches and institutes worldwide.
A complex system of inspection and maintenance is in place to inspect and maintain roads, bridges, tunnels and other installations. Based on visual inspection structures like bridges are inspected regularly. In case of concerns which cannot be resolved in this process, a procedure “Object Oriented Damage Analysis” has been put into place where additional inspection methods, especially NDT methods, are being utilized.
NDT methods to establish material properties such as strength, porosity, moisture, carbonation, etc need more attention to strengthen the links between engineers and inspectors. BAM and TU Berlin have established a joint Junior Professor to address this research area with gravity.
Research is currently focused on methods, data, validation, certification and standardization. Industry 4.0 has become a widely discussed topic with unforeseeable impact. Current research topics include
- Large Aperture UltraSound (LAUS) to evaluate very thick concrete elements (> 1m)
- Embedded ultrasound sensors to monitor changes in concrete
- Data fusion algorithms for honeycomb detection, corrosion localization and reinforcement diameter determination
- Reverse Time Migration to improve imaging of concrete structures
- Laser Induced Breakdown Spectroscopy (LIBS) with new applications, improved sensitivity and resolution, new devices
- RFID based humidity and corrosion sensors
- Analysis of scattered Radar waves for the classification of concrete
- Development of reference specimens for selected NDT tasks
The presentation will present examples of current research and ideas for research directions.
We present the results of a machine learning (ML)- inspired data fusion approach, applied to multi-sensory nondestructive testing (NDT) data. Our dataset consists of Impact-Echo (IE), Ultrasonic Pulse Echo (US) and Ground Penetrating Radar (GPR) measurements collected on large-scale concrete specimens with built–in simulated honeycombing defects. In a previous study we were able to improve the detectability of honeycombs by fusing the information from the three different sensors with the density based clustering algorithm DBSCAN. We demonstrated the advantage of data fusion in reducing the false positives up to 10% compared to the best single sensor, thus, improving the detectability of the defects. The main objective of this contribution is to investigate the generality, i.e. whether the conclusions from one specimen can be adapted to the other. The effectiveness of the proposed approach on a separate full-scale concrete specimen was evaluated.
Laser-induced breakdown spectroscopy (LIBS) is a combination of laser ablation and optical emission spectroscopy. Due to the possibility of direct measurements on the sample surface with a minimum of sample preparation investigations of building materials can be conducted quite fast. In combination with a scanning technique (translation stage or scanning mirrors head) 2D element distributions of harmful species like chlorides and alkalis are evaluated with a sub-mm resolution. By scanning a surface of typically 100 mm x 100 mm the heterogeneity of the material may be considered. LIBS is capable to identify hot spots in element concentration with a resolution of 0.1 mm or even smaller. A LIBS-system for the on-site application on building materials is, in cooperation with system developers and companies which will use this technique for investigation on real structures, under test at BAM. We present an example. Further work will focus on providing guidelines to establish LIBS as a standard procedure for chemical investigations of building materials.