TY - THES A1 - Kind, Thomas T1 - Signatur der Streuung von Radarwellen durch die Heterogenität von Beton N2 - Das Radarverfahren ist ein schnelles bildgebendes Verfahren für die Untersuchung der inneren Struktur von Stahlbeton-Bauwerken und wird seit längerem erfolgreich für die zerstörungsfreie Untersuchung von Brückenbauwerken eingesetzt. Für die Rekonstruktion der Lage der Bewehrung reicht die Annahme einer homogenen Materialeigenschaft des Betons meistens aus. Nähere Untersuchungen der empfangenen Streuungen der Radarwellen zeigen, dass neben der starken Streuung der Radarwellen an den metallischen Einbauteilen auch schwache Streuungen existieren. Diese schwachen Streuungen im Beton wurden nun erstmals in dieser Arbeit untersucht und können der Heterogenität des Betons zugeordnet werden. Die schwachen Streuungen entstehen durch den Permittivitätskontrast und die Geometrie der Gesteinskörnung im umgebenden Zementstein des Betons. Im Rahmen dieser Arbeit wurden die schwachen Streuungen im Beton für unterschiedliche Gesteinskörnungen charakterisiert und der Einfluss des Wellenlängenbereichs der Radarwellen auf die Ergebnisse untersucht. Weiter zeigt die Arbeit, dass die Streuungen an der Gesteinskörnung einen wesentlichen Einfluss auf die maximale Eindringtiefe von Radarwellen in Beton haben. N2 - The radar method is a rapid imaging technique for the study of the internal structure of reinforced concrete structures and has been used successfully since some time for non-destructive analysis of bridge structures. For the reconstruction of the position of the reinforcement, the assumption of homogeneous material properties of concrete is usually sufficient. More detailed investigations of the received scattering of the radar waves show that in addition to the strong scattering of the radar waves at the metallic mounting parts also weak scattering exists. These weak variations of scattering in the concrete were investigated for the first time in this thesis and are assigned to the heterogeneity of the concrete. The weak scattering is caused by the contrast of the permittivities and the geometry of the aggregate of the surrounding concrete cement paste. In this thesis, the weak scattering in concrete was characterized for different aggregates and the influence of the wavelength range of the radar wave on the results was investigated. Further, the thesis shows that the variations in the aggregate have an essential effect on the maximum propagation length of radar waves in concrete. T3 - BAM Dissertationsreihe - 138 KW - Heterogenität KW - Zementstein KW - zerstörungsfreie Prüfung (ZfP) KW - Gesteinskörnung KW - Interferenzmuster KW - heterogeneity KW - cement stone KW - non destructive testing (NDT) KW - aggregates KW - interference pattern PY - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-5682 SN - 978-3-9817149-9-9 VL - 138 SP - 1 EP - 103 PB - Bundesanstalt für Materialforschung und -prüfung (BAM) CY - Berlin AN - OPUS4-568 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kind, Thomas A1 - Trela, Christiane A1 - Schubert, Marcus T1 - Detection of air voids in concrete by radar in transmission mode by radar in transmission mode T2 - 8th International Workshop on Advanced Ground Penetrating Radar - IWAGPR 2015 CY - Florence, Italy DA - 2015-07-07 PY - 2015 AN - OPUS4-34434 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kind, Thomas T1 - Automatisierung von Radarmessungen für die Praxis und Forschung im Bauwesen T2 - 11. Georadar Rundtisch-Gespräch CY - Aachen, Germany DA - 2015-10-01 PY - 2015 AN - OPUS4-34436 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Kind, Thomas T1 - Amplitudes Variation of GPR Rebar Reflection Due to the Influence of Concrete Aggregate Scattering T2 - International Symposium Non-Destructive Tesing in Civil Engineering (NDT-CE 2015) CY - Berlin, Germany DA - 2015-09-15 PY - 2015 AN - OPUS4-34438 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Trela, Christiane A1 - Kind, Thomas A1 - Schubert, Marcus T1 - Detection of air voids in concrete by radar in transmission mode N2 - Air voids in concrete like honeycombs are one of the major concerns regarding quality assurance for the construction of infrastructure buildings like bridges or tunnels. This paper shows that voids in reinforced concrete walls or slabs can be detected by two standard ground coupled GPR antennas in transmission mode using a two-side zero-offset profiling configuration like in borehole radar applications. For the detection of voids only the amplitudes of the direct wave in transmission mode are evaluated. Even when the depth of the void can not be detected in this configuration, the major advantage of the zero-offset profiling in transmission mode is a lower interference with the surrounding reinforcement compared to a regular one-side reflection profiling. The capability of the two-side zero-offset profiling is demonstrated on a test specimen with a set of polystyrene balls of two different sizes representing voids like honeycombs in concrete. GPR measurements are realized by an automated scanning system in order to allow for a synchronous movement of the antennas. In transmission mode voids can be detected at greater depths compared to reflection mode, since the travel path of the direct wave is half as long. Another characteristic of the transmission mode is that the direct wave through the air voids is faster and arrives earlier than the direct wave in the surrounding concrete. Hence it can be separated from the strong reflection of the reinforcement. Finally the measurements in transmission mode are less sensitive to the antenna frequency and polarization than in reflection mode. T2 - IWAGPR 2015 - 8th International workshop on advanced ground penetrating radar CY - Firenze, Italy DA - 07.07.2015 KW - Radar KW - Zerstörungsfreie Prüfung KW - Ground penetrating radar KW - Transmission KW - Reinforced concrete KW - Honeycombs KW - Void detection KW - First arrival PY - 2015 SN - 978-1-4799-6495-6 U6 - https://doi.org/10.1109/IWAGPR.2015.7292650 AN - OPUS4-34678 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Trela, C. A1 - Kind, Thomas A1 - Günther, Martin T1 - Ground penetrating radar in reflection vs transmission mode for void detection in concrete structures N2 - The concreting of prefabricated concrete structures can lead to insufficient bonding or even to remaining cavities. Honeycombs (aggregate clusters without cement) represent potential weakening of the structure and need to be detected non-destructively. In our study we tested the capability of ground penetrating radar (GPR)techniques for this purpose. We applied GPR in reflection mode and zero-offset profiling (ZOP) Transmission mode on a precast concrete twin wall with built-in honeycombs. GPR measurements were performed as twochannel measurement with ground coupled antennas with centre frequencies of 1.5 GHz and 2.6 GHz mounted to an automated scanner system. Our findings show that ZOP transmission measurements are a more efficient method to detect voids in reinforced concrete structures compared to reflection mode measurements. This holds for both the effort needed for the measurement and the evaluation as well as the validity of the data. Honeycombs (basically representing voids) are usually characterized by strongly reduced amplitudes and earlier arrivals of the transmitted wave. T2 - NDT-CE 2015 - International symposium non-destructive testing in civil engineering CY - Berlin, Germany DA - 15.09.2015 KW - Ground penetrating radar KW - Reflection KW - Transmission KW - Reinforced concrete KW - Prefabricated wall KW - Void detection PY - 2015 SN - 1435-4934 SP - 324 EP - 344 PB - Technische Universität Berlin / Bundesanstalt für Materialforschung und -prüfung CY - Berlin, Germany AN - OPUS4-40006 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kind, Thomas T1 - Amplitudes variation of GPR rebar reflection due to the influence of concrete aggregate scattering N2 - 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. T2 - NDT-CE 2015 - International symposium non-destructive testing in civil engineering CY - Berlin, Germany DA - 15.09.2015 KW - Ground penetrating radar KW - Concrete KW - Rebar KW - Aggregate scattering PY - 2015 UR - http://www.ndt.net/?id=18402 SN - 1435-4934 VL - 20 IS - 11 SP - 412 EP - 420 PB - NDT.net CY - Kirchwald AN - OPUS4-40007 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -