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- Radar (24)
- Zerstörungsfreie Prüfung (13)
- Ground penetrating radar (7)
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- Ultraschall (6)
- Zerstörungsfreie Prüfung im Bauwesen (6)
- Concrete (5)
- Non-destructive testing (5)
- GPR (3)
- Ground penetrating radar (GPR) (3)
Organisationseinheit der BAM
- 8 Zerstörungsfreie Prüfung (7)
- 8.2 Zerstörungsfreie Prüfmethoden für das Bauwesen (7)
- 7 Bauwerkssicherheit (4)
- 8.6 Faseroptische Sensorik (3)
- 2 Prozess- und Anlagensicherheit (2)
- 2.4 Prüfung und Bewertung von Explosivstoffen/Pyrotechnik (2)
- 2.5 Konformitätsbewertung Explosivstoffe/Pyrotechnik (2)
- 7.4 Baustofftechnologie (2)
- 7.1 Baustoffe (1)
- 7.2 Ingenieurbau (1)
Eingeladener Vortrag
- nein (17)
Ground penetrating radar (GPR) was used to characterize the frequency-dependent dielectric relaxation phenomena in ordinary Portland cement (OPC) hydration in concrete changing from fresh to hardened state. The study was experimented by measuring the changes of GPR A-scan waveforms over a period of 90 days, and processed the waveforms with short-time Fourier transform (STFT) in joint time-frequency analysis (JTFA) domain rather than a conventional time or frequency domain alone. The signals of the direct wave traveled at the concrete surface and the reflected wave from an embedded steel bar were transformed with STFT, in which the changes of peak frequency over ages were tracked. The peak frequencies were found to increase with ages and the patterns were found to match closely with primarily the well-known OPC hydration process and secondarily, the evaporation effect. The close match is contributed to the simultaneous effects converting free to bound water over time, on both conventional OPC hydration and dielectric relaxation mechanisms.
Time slices of very dense GPR measurements carried out at concrete with a real point distance of less than 10 mm in x and y direction show weak reflection patterns besides the strong reflections of reinforcements. A repetition of these measurements with the same local geometrical precision at the same specimen shows the same reflection pattem. We suppose that the heterogeneity of concrete given by aggregates (e.g. gravel, broken granite) causes local weak Scattering of the GPR waves and leads to reflection patterns in the GPR data. These reflection patterns can be explained by a Superposition of multiple scatterings of single aggregates. So far these reflection patterns have been not recognized in Standard time slices due to the large spacing (> 5 cm) between single profiles and because of the interpolation between the profiles.
We investigate the characteristics of the volume scattering effects, caused by aggregates, at concrete blocks with two different grading curves. In a more general investigation we study the volume scattering of aggregates by using wooden boxes filled with only typical aggregates and an included defined reflector (metal plate). The thickness of the aggregate layer above the metal plate was varied between 20 cm and 40 cm. With a very dense measuring grid at the surface we are able to calculate the effective volume scattering and to analyze the distribution of the reflection amplitude of the included metal plate for different aggregate set-ups. Results of this study confirm that the weak reflection patterns in concrete can be explained by aggregate scattering and have a direct correlation to the penetration depth of GPR in concrete.
Amplitudes Variation of GPR Rebar Reflection Due to the Influence of Concrete Aggregate Scattering
(2015)
Amplitudes variation of GPR rebar reflection due to the influence of concrete aggregate scattering
(2015)
Dense GPR measurements of rebar reflection amplitudes Show relative variations, which can be in the order of more than 10% - 20%. Former investigations demonstrated that these variations are caused by the heterogeneity of concrete, i.e. due to the inclusion of aggregates in concrete. These amplitude variations make it difficult to analyse single reflection amplitudes in order to determine the rebar diameter or to estimate the concrete deterioration state. In a systematic study we have quantified the statistical variation of the rebar reflection amplitude for concrete covers of 6 cm, 9 cm, 12 cm, 15 cm and 18 cm, for two different grading curves and for the rebar diameters 12 mm and 28 mm. Also the influence of the wavelength has been investigated by using antennas with different centre frequencies in relation to the aggregate size. The results are discussed with regard to a quantitative amplitude evaluation of GPR measurements and also the potential of using these variations for a characterization of concrete material properties.
Application of georadar for the determination of moisture content and distribution in masonry
(2003)
The application of impulse radar for structural investigation of concrete elements has been increased during the last years related to technical developments, i. e. of high frequency antennas. In this paper, case studies will be presented related to the location of reinforcing bars, tendon ducts and repaired concrete areas in concrete bridges, anchors and dowels in concrete highways and delaminations of layered structures as they are used for non-ballasted railway tracks. It is shown that impulse radar can be applied in case of regular inspection and for searching the cause of damages but also for quality assessment in civil engineering.
Bereits seit vielen Jahren stehen Anwendern der zerstörungsfreien Prüfung im Bauwesen (ZfPBau) zuverlässige Geräte zur Untersuchung von Betonbauteilen zur Verfügung. Viele dieser Geräte zeichnen eine Messgröße in Bezug zum Messort auf und sind je nach Ausstattung in der Lage, die Ergebnisse in einem Koordinatensystem darzustellen. Doch erst die Kombination verschiedener ZfPBau-Verfahren an einer Messfläche erlaubt den maximalen Informationsgewinn über die innere Konstruktion von Stahlbeton- und Spannbetonbauteilen. In dem Beitrag wird ein Bauwerkscanner zur automatisierten und kombinierten Datenaufnahme beschrieben, der erstmals die Kombination von Radar, Ultraschall und Wirbelstrom mit Datenausgabe in einem einheitlichen Koordinatensystem ermöglicht. Dieser Scanner ist im Gegensatz zu früheren Systemen technikerbasiert und erlaubt im Bedarfsfall eine spätere detaillierte Auswertung durch ZfP-Spezialisten. Die Ergebnisse werden bildgebend in frei wählbaren Schnitten dargestellt, was bereits kurze Zeit nach der Messung auf der Baustelle möglich ist. Am Beispiel eines Brückenträgers wird gezeigt, wie der tatsächliche Spanngliedverlauf aus Messdaten ermittelt wird und dem angenommenen Verlauf gemäß Bestandsplan gegenübergestellt wird. Damit kann künftig eine Überprüfung von Bestandsplänen durchgeführt werden. Darüber hinaus könnten nicht vorhandene Bestandspläne rekonstruiert werden. Des Weiteren wird am gleichen Brückenträger gezeigt, wie sich ein echter Verpressfehler und im Unterschied dazu ein Luftspalt in einem Hüllrohr in Messdaten abbilden. An dem Beispiel wird deutlich, wie Ultraschallergebnisse in Kombination mit Phasenauswertung zur Formulierung von Verdachtsstellen für Verpressfehler eingesetzt werden können und welche Maßnahmen zur Verifizierung getroffen werden müssen.