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Erscheinungsjahr
- 2015 (5) (entfernen)
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- Englisch (5)
Schlagworte
- Dry contact transducers in boreholes (2)
- Interface salt-concrete / rock salt (2)
- Ultrasonic imaging of internal reflectors (2)
- Ultrasonic reflection measurement (2)
- Acoustic test (1)
- Betonbauteile (1)
- Commercial acoustic devices (1)
- Composite materials (1)
- Concrete bridges (1)
- Concrete specimens (1)
For almost 15 years, carbon fibre-reinforced polymer (CFRP) plates and sheets have been used for strengthening and repair of civil engineering structures. CFRP plates were applied to upgrade structures for change in use or increasing traffic load. CFRP laminates have also been used to repair deteriorated structures such as multi-storey parking or bridges. The execution quality and condition of the strengthening measure in terms of bond integrity were neither monitored nor tested systematically. Inspectors eventually applied simple hammer knocking during regular main inspection for subjective noise distinction as a measure for eventual insufficient bond. This paper presents the feasibility and the limitations of low-frequency transversal ultrasonic waves with dry-coupling point-contact sensors for inspection and defect detection between CFRP laminate and concrete surfaces. The German Centre of Competence in Civil Engineering (DIBt) has initiated a national research project [Helmerich et al. (2012). Condition analysis of bonded CFRP-applications on concrete structures by means of non-destructive testing [in German: Zustandsuntersuchung von CFK-Klebeverstärkungen an Betonbauteilen mittels zerstörungsfreier Prüfung (ZfP)]. Final, internal project report], carried out at the Federal Institute for Materials Research and Testing (BAM), Germany. The aim of the project was to present a potential non-destructive testing method for bond defect detection as a measure for the durability of the strengthening system more than 10 years after application.
Cracks perpendicular to the surface may be initial indicators for a deterioration process of concrete structures. Moisture penetrates inside the structure and transports adverse chemicals. The paper presents an investigation about the reliability of available commercial non-destructive evaluation techniques to reliably estimate the depth of surface-breaking cracks in reinforced concrete structures. Aim of the study was the investigation of surface-braking cracks under laboratory conditions. Commercial acoustic devices as impact echo equipment, single ultrasonic transducers and arrays were applied even if they have not been developed for this purpose. The commercial software and descriptions for application was followed strictly to compare the function, precision and repeatability of the measurements. Both, perpendicular notches and cracks have been considered. The study was completed with a discussion about reference specimens. The study was the basis for formulation of gaps in research. The Electric Power Research Institute (EPRI) has initiated and funded a Project.
For the closure of radioactive waste disposal facilities engineered barriers- so called “drift seals” are used. The purpose of these barriers is to constrain the possible infiltration of brine and to prevent the migration of radionuclides into the biosphere. In a rock salt mine a large scale in-situ experiment of a sealing construction made of salt concrete was set up to prove the technical feasibility and operability of such barriers. In order to investigate the integrity of this structure, non-destructive ultrasonic measurements were carried out.
Therefore two different methods were applied at the front side of the test-barrier:
1 Reflection measurements from boreholes
2 Ultrasonic imaging by means of scanning ultrasonic echo methods This extended abstract is a short version of an article to be published in a special edition of ASCE Journal that will briefly describe the sealing construction, the application of the non-destructive ultrasonic measurement methods and their adaptation to the onsite conditions -as well as parts of the obtained results. From this a concept for the systematic investigation of possible contribution of ultrasonic methods for quality assurance of sealing structures may be deduced.
Investigations for the improvement of SAFT imaging quality of a large aperture ultrasonic system
(2015)
In parallel to the hardware development of an ultrasonic system for the investigation of thick concrete structures, a software package for interactive reconstruction of data for that special arrangement of ultrasonic transducers was developed. The system which is presented in a further contribution to this conference as "large aperture ultrasonic system" (LAUS) requires special features to the evaluation software because measuring positions can be in a non equidistant grid and there is the possibility to improve the measurement by adding measuring points interactively.
Starting from theoretical considerations to the image generation by measuring arrangements of synthetic aperture problems, solution approaches for imaging with SAFT (Synthetic Aperture Focusing Technique) algorithms in space and frequency domain of data from insufficient grid density are presented.
A wide range of issues that may arise in the application is precalculated by simulations and experimental studies, so that unavoidable artifacts can be identified and classified. A special focus is put on the application of thick concrete structures considering missing measuring points in a grid, grating lobes and surface waves.