Ein Ultraschallsystem mit großer Apertur, genannt LAUS – Large Aperture UltraSound, wird vorgestellt und die technischen Eigenschaften erläutert. Es besteht aus zwölf Prüfköpfen, die beliebig auf Betonoberflächen mit Unterdruck befestigt und jeweils als Sender oder Empfänger genutzt werden. Alle möglichen Kombinationen ergeben 132 Einzelmessungen, die zur Rekonstruktion des durchschallten Volumens genutzt werden. Das System wurde an zwei Bauwerken erfolgreich erprobt. Die Dicke einer sehr stark bewehrten Fundamentplatte eines Fallturms wurde bestimmt. Die Messungen erfolgten in einem Raster auf einer Fläche von 2,0 × 1,8 m2 und die Rückseite konnte eindeutig abgebildet werden. Weitere Anzeigen aus dem Inneren der Platte zeigen das Potenzial des Systems. An einem Brückenbauwerk wurden indirekt Verdichtungsmängel lokalisiert. Dazu wurden mit dem LAUS‐System die im Brückenträger verlaufenden Spannkanäle durch fast 2 m Beton abgebildet.
roded reinforcing mesh. In indoor slabs, delamination typically appears as a single, shallow, horizontal, near-surface separation oriented parallel to the finished surface. Delamination may affect areas as small as a few square inches to more than 100 ft 2 and occurs at a depth ranging from very shallow [ 1 ⁄16 in. or (1.6 mm)] to 3 ⁄4 in. (20 mm) or deeper in the outdoor slabs (2, 3).Jana (2) has summarized the common causes of delamination as (a) the use of air entrainment in a concrete slab receiving a handtrowel finish; (b) machine-trowel finishing a lightweight aggregate concrete slab; (c) premature finishing of a slab before the cessation of bleeding; (d) top-down stiffening or surface crusting of a concrete slab under hot, windy, or dry weather conditions, especially if the slab is undergoing slow and prolonged bleeding; (e) prolonged finishing operations on an outdoor air-entrained concrete slab or on a slab receiving a mineral or metallic surface hardener; ( f ) corrosion of reinforcing steel in concrete due to chloride ingress or carbonation; and (g) cyclic freezing and thawing of a poorly or non-air-entrained concrete slab at critically saturated conditions.No matter what the underlying cause, delamination is a nuisance in in-service concrete slabs. Delaminations grow over time and may eventually develop into large planes of separation that result in surface peeling and spalling. In concrete bridge decks, delamination is regarded as an indirect indication of severe steel rebar corrosion, and thus the extent of delamination measures the severity of deck deterioration. To take timely preventive measures and to avoid the high cost of bridge deck demolition and reconstruction, early detection of delaminations is necessary. Bridge owners and highway agencies have long been conducting so-called traditional deck surveys including visual ones, electromechanical sounding, hammer sounding (i.e., metal tapping), and chain drag (ASTM D4580-03) for routine inspection and identification of delaminated zones in bridge decks (and rigid pavements). More sophisticated nondestructive testing (NDT) techniques such as ground-penetrating radar and impact echo (IE) have been recently adopted by some transportation agencies (4). Among other NDT techniques, activepassive infrared thermography has demonstrated great potential for detection of shallow delaminations (ASTM D4788-03). Implementing such advanced techniques offers several advantages over the common practice of traditional surveys, including reducing the number of necessary cores and the cost associated with the coring operation, obtaining a more objective condition assessment, detecting deterioration at its early stages of development, and full coverage of the test deck with minimal or no traffic interruption. The ultimate anticipated value-added is a reduction in the overall life-cycle costs.
Nondestructive testing of concrete structures plays an increasing role in civil engineering, although until now the full potential of such techniques has not been tapped. For posttensioned structures, the investigation of tendon ducts is one of the most essential testing problems. The location of tendon ducts, the determination of concrete cover and, especially, the detection and quantification of ungrouted areas inside the ducts are the relevant questions. Recent developments and opportunities of radar, impact-echo, and ultrasonics for the investigation of tendon ducts are presented. Although the obtained results on positioning and concrete cover determination are sufficient, the location of ungrouted areas is still a matter of research. Thus, new approaches for this testing problem have to be considered. Additionally, the combined use of complementary techniques offers a high potential to increase the reliability of results. Data will be displayed on the combined application of acoustic and electromagnetic impulse-echo methods and of data fusion related to the investigation of tendon ducts.
Zerstörungsfreie Prüfverfahren im Bauwesen (ZfP‐Bau) dienen der Zustandsermittlung von Bauteilen und der Erkundung unzureichend dokumentierter Bausubstanz. Zur Untersuchung von Fundamentplatten wird das Ultraschallecho‐Verfahren vorgestellt. Es werden Anwendungshinweise zur Durchführung von Dickenmessungen, dem Lokalisieren von Pfählen und Streifenfundamenten unter einer Fundamentplatte gegeben. Anwendungsbeispiele für Untersuchungen an 30 cm, 75cm und 125 cm dicken Fundamentplatten mit verschiedenen Bewehrungsgehalten werden beschrieben. Darüber hinaus wird die bildgebende Darstellung der Ergebnisse, z. B. die Abbildung eingebauter Bewehrung, vorgestellt.
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