Hans-Joachim Wichmann

Non-destructive measurement toolkit for corrosion monitoring and fracture detection of bridge tendons

One of the most considerable challenges of building management is to ensure the integrity and the functionality of prestressed members during service life. But particularly corrosive and mechanical influences on the prestressing steel reinforcement strongly impair the long-term performance and durability of interior as well as of exterior tendons in concrete bridges and of other prestressed structures. The durability state and degradation of tendons can be assessed primarily on the basis of the tendons force, the corrosion state and the existence of steel fractures. For the determination of these parameters, this paper will briefly report on the application and practical verification of a measurement toolkit, which is used for monitoring, inspecting and testing of prestressed concrete elements, with main consideration of prestressed tendons in bridges. This toolbox comprises conventional inspection and several innovative measurement and monitoring techniques, which have been developed, tested and optimised by the authors in the last decade.

Assessment of the State of Condition of Prestressed Concrete Structures with Innovative Measurement Techniques

The reliability of tensile elements is a requirement for the safety of prestressed structures. Besides many other data, the assessment of the load-carrying capacity of a prestressed concrete structure requires the knowledge of the actual force of the tendons and their corrosion state as well as the localization of fractures. Neither for grouted interior nor for ungrouted exterior tendons non destructive and reliable methods to measure the prestress and to assess the corrosion activity or to locate tendon fractures are available today. This contribution reports on actual research projects, dealing with fiber optic sensors to measure deformations and dealing with the variation of high frequency damping of steel tendons in concrete members due to corrosion. Furthermore a high-frequency-method is used to locate fracture in tendons. First applications of some of these innovative techniques on a real structure are presented: the Herrenbrücke-bridge in Lübeck. Since three winters, measurements on this prestressed concrete bridge assessing its state of condition are carried out.

Verbesserte Sensormessverfahren für das Dauerhaftigkeitsmonitoring von Betonbauwerken

Durch geeignete Monitoringmasnahmen sind dauerhaftigkeitsrelevante Eigenschaften sowie Zustands- und Schadigungsgrosen in Stahl- und Spannbetonbauwerken objektiv, reprasentativ und zuverlassig bestimmbar. Dadurch konnen geeignete Erhaltungsmasnahmen rechtzeitig ergriffen und wirtschaftlich optimiert durchgefuhrt werden. In diesem Beitrag wird ein Messtechnikpaket mit verschiedenen neuartigen sensorbasierten uberwachungsmethoden fur das Dauerhaftigkeits- und Korrosionsmonitoring von Betontragwerken vorgestellt. uberwachungsgrosen sind dabei die Permeabilitat, die Feuchte, der freie Chloridgehalt und die Korrosionsgefahr im Beton. Der Schwerpunkt liegt in der Erorterung des aktuellen Standes der Forschung mit den Messgrundlagen, wesentlichen Erkenntnissen und Weiterentwicklungen dieser am iBMB der TU Braunschweig entwickelten Einbausensorik.