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- Non-destructive testing (6) (entfernen)
Die Bestimmung der Belegreife von Estrichen erfolgt im Bauwesen meist unter Verwendung von zerstörenden Verfahren, die Probenentnahmen erfordern und nur punktuelle Daten liefern. Bei anhydritgebundenen Estrichen gelten 0,5 M% und bei zementgebundenen ca. 3,5 M% und höher als belegreifer Feuchtegehalt. Die Belegreife wird als Feuchtegehalt in Masseprozent (M%) bezogen auf die Trockenmasse des Baustoffes angegeben. Zur zerstörungsfreien Feuchtemessung existieren verschiedene einfach zu bedienende Handgeräte, die u. a. auf elektrischen, elektromagnetischen und kapazitiven Methoden beruhen. In dieser Arbeit wurden ein kapazitives (Kugelsonde), ein elektromagnetisches (Mikrowellensensoren) und ein elektrisches Messverfahren (Vierelektroden-Sonde) untersucht. Mit Ausnahme der Vierelektroden-Sonde weisen die Handgeräte keine ausreichende Sensitivität in Bereichen niedriger Feuchtegehalte unterhalb von 1 M% auf und scheinen somit nicht für anhydritgebundene Estriche geeignet zu sein. Für zementgebundene Estriche lassen sich hingegen mit allen getesteten Geräten Änderungen in dem Bereich der Belegreife erfassen. In dieser Arbeit wird zusätzlich die Wasserabgabe in g/m²/Tag als Bezugsgröße herangezogen. Die Wasserabgabe stellt ein geeigneteres Maß für die Schadensträchtigkeit dar und ermöglicht direkte Vergleiche unabhängig von der verwendeten Estrichart. Für alle getesteten Estriche konnte eine Wasserabgabe von ca. 8-10 g/m²/Tag als Belegreifegrenzwert bestimmt werden.
Trans-European corridors for transport of people and goods require strengthening of bridges to carry increased axle loads in terms of absolute axle loads and of their frequency. Most of the bridges along highways are reinforced or prestressed concrete bridges.
Since the late 1990s, CFRP laminates have been applied to box girder and T-beam bridges to increase the overall capacity. Although regular inspections are carried out, no special method was available to test the bond condition of CFRP laminates after being in Service for more than ten years. The German Center of Competence in Civil Engineering is aware of this need and funded a research project to investigate the bond condition by means of advanced non-destructive testing (NDT).
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.
Moisture ingress is one of major damaging factors for masonry buildings. As the complex resistivity (CR) is sensitive to textural properties as well as to the pore fluid chemistry of wet porous media, its non-destructive application can provide helpful information for conservators. In a comprehensive laboratory study it has been shown that CR might even be able to distinguish between salt content and saturation degree in only one measurement. The combined use of electrical and electromagnetic measurement techniques in two field-scale flooding experiments has shown some unexpected differences. Possible reasons are discussed and it is shown that bringing together the information of both methods leads to a clearer picture.
Non-destructive testing (NDT) of concrete structures is performed using pulse-echo methods. According to the type of the applied waves it can be classified as acoustic (Impact-Echo, Ultrasonics) and electromagnetic methods (Radar). The results are visualised through different imaging processes. This work is performed in the frame of a research project promoted by Deutsche Forschungsgemeinschaft (FOR384). The objective of data fusion is to use the complementary information of the different methods. Radar can detect metallic reflectors in concrete (metallic ducts and concrete reinforcement) very well. This method is not able to locate defects behind these reflectors (injecting defects, defects behind close concrete reinforcement), because the electromagnetic waves are completely reflected at metals. The acoustic methods are able to compensate this deficit i.e. Acoustic waves can penetrate through metal. But acoustic waves in the ultrasonic range are completely reflected by air layers. Air layers have smaller influence on radar propagation, so that both methods complement each other. In order to be able to combine the NDT-data from several methods records at the same volume, the different data setsmodes of signals must be adapted. The ultrasonic and radar data have to be reconstructed with programs based on the Synthetic Aperture Focusing Technique (SAFT) before data fusion. Subsequently, a conversion of the data into a uniform format has to be carried out. This is a prerequisite in order to keep the data exchange between the project partners as simple as possible. After the data sets are imported and transferred into a common reference system, they can be processed with operations according to the purpose of the investigation. Results, which have been achieved in concrete test specimen with radar and ultrasonics, will be presented and will show the feasibility of the data fusion method.