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Eingeladener Vortrag
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Since several years ultrasonic imaging techniques are used for testing concrete elements. Combined with a reconstruction calculation they lead to an acoustic imaging of scatterers and reflectors from the inside of the concrete element. For several testing problems it is an advantage to use a two dimensional synthetic aperture and to combine it with a three-dimensional reconstruction calculation (3D-SAFT, Synthetic Aperture Focussing Technique).
This enables the analysis of the tested volume by means of B-scans in two directions and C-scans (projections parallel to the surface), respectively. Using the 2D-scanning technique, especially the disturbing influence of the reinforcing rebars can be minimised.
In this contribution the state of the art of this method is demonstrated and analysed. Examples of the application are presented, concerning
Localisation of honeycombing and compaction faults
Characterisation of cracks (especially measuring the crack depth)
Investigation of tendon ducts
The results presented are obtained in the frame of a research initiative Non-destructive Evaluation of Concrete Structures Using Acoustic and Electromagnetic Echo-Methods supported by the German Science Council (FOR 384 of DFG, Deutsche Forschungsgemeinschaft). The methods are assessed and improved in cooperation with the partners participating in the project.
Ultrasonic investigation is an established non-destructive testing method for detection of defects and material characterisation. In the last years scanning ultrasonic echo methods were developed especially for the application in civil engineering.
The different scanning ultrasonic echo methods are modified with respect to the type of the transducer applied, the number and the arrangement of transducers and the frequency used. Also different algorithms are used to analyse the measured data, for instance SAFT (Synthetic Aperture Focusing Technique) reconstruction. The results are typically presented as B- and C-scans, obtained from raw data or the SAFT reconstructed data.
Since 2001 several German research institutes co-operate within the scope of the research initiative Non-destructive Evaluation of Concrete Structures Using Acoustic and Electromagnetic Echo-Methods (FOR 384) supported by the Deutsche Forschungsgemeinschaft (DFG). One of the tasks is to investigate these ultrasonic echo methods for special applications like the detection of cavities in concrete structures or faults in tendon ducts.
Concrete test specimens with intentional faults have been manufactured and investigated. Parameters were defined to assess the results more objectively. Currently three parameters -signal/noise-ratio, lateral edge resolution and uniformity- are considered. For the first time results of different working groups on the same imaged objects are compared quantitatively. It should help to get more knowledge about the ultrasonic inspection of typical faults in civil engineering structures.
Non-destructive Testing of a Post tensioned Concrete Bridge Applying an Automated Measuring System
(2004)
Assessment of post tensioned concrete bridges applying automated non-destructive testing systems
(2005)
Results of reconstructed and fused NDT-data measured in the laboratory and on-site at bridges
(2006)
Non-destructive testing (NDT) of concrete structures plays an increasing role in civil engineering. This paper presents the results of measurements carried out in the laboratory at BAM and on-site at several bridges using reconstructed and fused radar and ultrasonic echo data sets. In this context different scanning systems, developed for the on-site application of NDT-methods (e.g. reinforced concrete bridges) are introduced. The main object was the demonstration of the improved effectiveness of radar and ultrasonic pulse echo technique due to the automated measurements and the application of new software for the data processing and data visualisation. The results of these measurements show the high potential of reconstruction and data fusion for the improvement and simplification of the interpretability of large data sets measured with impulse-echo methods.
Assessment of post tensioned box girder bridges applying automated non-destructive testing methods
(2006)
Ultrasonic Reflection Properties at Interfaces Between Concrete Steel and Air: Imaging and Modelling
(2006)
Automated NDE of post-tensioned concrete bridges using radar, ultrasonic echo and impact-echo
(2006)
This paper presents the progress of successful location of grouting faults in tendon ducts with ultrasonic imaging. The examples were obtained in the research group FOR 384 funded by DFG (German Research Foundation). The co-operation of experimental research and modeling allowed imaging and identification of grouted and ungrouted areas of tendon ducts (including strands) in a large test specimen (40 m²). In addition to the criteria for indicating grouting faults in post-tensioned ducts known until now the phase evaluation of reflected ultrasonic pulses is described. Experiments and modeling of wave propagation are presented for reflections at metal plates in concrete (thickness range 0.5 mm to 40 mm) and for tendon ducts including strands.
The main part of the progress was achieved by automated measurements using dry contact transducers, 3D-SAFT reconstruction including phase evaluation and modeling considering wave propagation for typical elastic parameters and exact experimental site conditions. The results for shear waves as well as for pressure waves are compared in the frequency range from 50 kHz to 120 kHz.
Influence of concret properties on the calibration of radar, ultrasonics and active thermography
(2008)
The European infrastructure asset has developed historically and is characterized by nation-specific construction processes. Inspection, condition assessment, and maintenance procedures differ from country to country. Because of historical and political circumstances, national infrastructure assets are maintained at different levels, too. Since the budget for maintaining the bridge infrastructure less and less meets the demands of a growing bridge stock, bridge inspection, maintenance, and life-cycle considerations gain higher importance. The need exists to develop effective diagnosis tools for early detection of construction faults, defects, and deterioration processes during inspection, to keep the bridge infrastructure at an acceptable level, from structural safety and economic viewpoints. An overview on the latest research projects and integrated bridge management systems in Europe is given. The potentials of nondestructive testing (NDT) are presented, with special focus on technical advances of NDT applications to reinforced concrete (RC) and posttensioned concrete bridges. Although NDT is not regularly integrated in these processes, the application brings valuable information on the current condition of the inner structure in called-in special inspections. NDT-automation and the application of imaging echo methods, combined with advanced data processing, produce a surprising level of information about the inner structure of massive RC slabs up to a depth of about 60 cm. Detected inhomogeneity and scatterers of acoustic or electromagnetic waves can be visualized in vertical or horizontal slices through the structure or animations. The fusion of different three-dimensional data sets of processed data improves the interpretability and accuracy of the results.
The introduction of an innovative process for non-destructive testing is described in terms of its different phases and how the process is controlled in the Fraunhofer IZFP in order to obtain optimal results. Examples are discussed of applications by IZFP in various important and safety-relevant industrial sectors where the automated inspection systems were introduced. These case studies include the inspection of railway components such as the wheel sets of the German high-speed train and in-line pipe inspection by using intelligent pipeline inspection gauges. Complex inspection systems, both hardware and software, developed in partnership with the Federal Institute for Materials Research and Inspection (BAM), were applied to inspection tasks in civil engineering. Two automated systems based on a robot and on a flexible manipulation are presented. Both systems can be applied to diverse inspection technologies and to the data fusion of various types of non-destructive testing (NDT) data.