International Symposium Non-Destructive Testing in Civil Engineering (NDT-CE) 26.-28.09.1995
Keywords: Catalogue Raisonne, Cooperation, Compendium, General Report, Research Activities

Supporting Processes

Simulation

Simulation procedures become more and more somewhat like a computer aided control or supplementation in the field of non-destructive testing in civil engineering. A deeper understanding of the problems which are linked to ultrasonic testing of concrete reveals the modelling of the ultrasonic wave propagation and that specific scattering in inhomogeneous materials /77/. Signal scans or the radar response image of concrete with voids and reinforcement /673/ can be predicted. The benefit of this is last but not least a control of real measurements and the possibility to recognize defects inspite of the inhomogeneous surroundings. The same considerations hold for the radar testing method. Advancement can be achieved through the understanding of electromagnetic properties of concrete in order to optimize the radar measurement parameters. With this view both, theoretical and experimental studies are reported /85/. Finally also for the ultrasonic pulse-echo method special effects in inhomogeneous materials like concrete and their influence on the images of testing data are analyzed and in conclusion characteristic values are formulated for the efficiency of this method /411 online/. To improve the interpretation of radar measurements the influence of the permittivity of building materials has been studied /375/1053/ as well as the influence of different geometries and parameters like sun heating or material's thermal properties on the results of infrared thermography /375/. Sometimes bridges or other big structures must be strengthened for example due to increasing traffic or must be altered in another way. In such cases with real measuring results of building dynamics the future load bearing behaviour can be predicted and optimized by sophisticated simulation /345/. Not inherent in simulation but anyhow related to this technique is the numerical reconstruction method which is often applied to inverse problems such as the calculation of the magnetisation distribution for detection of corrosion /365/.

Monitoring

By monitoring long-term controls of structures are possible with little expenditure of time if data acquisition units in connection with data submission by phone /361/ or telecontrolled data logging systems /1007/ are installed. Fiber optic sensors measure deformations and locate over- or under-straining, respectively, in the sense of detecting belonging defects /583/. Often monitoring systems are installed especially in concrete structures to watch steel corrosion in general /1215/ and the efficiency of the cathodic protection in particular /135/. Also specifically the corrosion risk due to chloride penetration is monitored /109/. In road structures the volumetric moisture content and the bulk electrical conductivity are registered /575/. For bridges a monitoring system continuously measures the static and dynamic part of the service loads and detects cracks or crack propagation /831/.

Instrumentation

At least for high stressed structures nowadays it is strongly advisable to construct structures in such a way that they can easily be tested or monitored by appropriate methods. For instance if a structural concrete member contains one empty duct running parallel with tendons, cracks and possibly corrosion could be detected and identified at any time by a remote magnetic measuring technique /1085/ With respect to the corrosion problem a multi-ring-electrode allows to determine the water distribution within the concrete cover between the reinforcement and the steel surface /1251/.

Robot Techniques

Steel reinforcing components can be imaged by employing a scanning inductive sensor which is motorised and moves across the concrete surface /1331/. Commonly known are the problems with sewers which develop after several years. For radar a flexible robot has been developed /429/.

Future Developments

In the past years great progress has been made in the field of non-destructive testing in civil engineering (NDT-CE) and this trend will certainly continue and even accelerate. Although many novel ideas and approaches have been advanced and improved instruments are being developed, new techniques are constantly being researched.

This development is highligthed by keywords like "maintenance or replacement", "quality control", "monitoring", "building inspection" and the like. Non-destructive testing in civil engineering will doubtless help outline future tasks and identify objects to be tested. Available solutions must be optimised. Testing strategies will have to be developed for special applications, e. g. how to use the different techniques, how to combine them with numerical calculations and neural networks, how to check the accuracy of test results and how to interpret them. This is exactly what ,,engineering" actually means and hence I would like to call this activities ,,Non-Destructive Civil Engineering (NDCE)". Potential users of NDT methods should be able to judge the benefits of the different techniques and test instruments. For this purpose a compendium in which about 80 different NDT-CE methods are explained and discussed was published in 1991 /L108/ and symposia were organized /L101/L102/L103/L107/ convening prominent experts from all over the world. It is hoped that this forthcoming conference will contribute to the advancement of NDT techniques and will provide a stimulus of international cooperation.

Literature

/1/... /757/	Page number of oral contribution in the proceedings of the NDT-CE Symposium 1995
/777/.../1339/	Page number of poster contribution in the proceedings of the NDT-CE Symposium 1995
/L101/	Malhotra, V. M. (editor): In-Situ/Nondestructive Testing of Concrete. aci Sp-82 (1984)
/ L102/	Bungey, J.H. (editor): Non-Destructive Testing in Civil Engineering. Proceedings Int. Conference, Liverpool, April 1993. The British Institute of NDT
/ L103/	Schickert, G.: NDT in Civil Engineering in Germany. pp. 45-64 in /102/
/ L104/	Proceedings 4th International Conference on Non-Destructive Testing of Works of Art, Berlin, October 1994, DGZfP, Berlin, Vol. 45
/ L105/	Feuchtetag '95, Moisture in Masonry, BAM/Berlin + FMPA/Weimar
/ L106/	Forschungsbericht 200 (Research Report Vol. 200): Zerstörungsfreie Prüfverfahren zur Bestimmung der Mauerwerksfeuchte, BAM/Berlin (1994)
/ L107/	Schickert, G. (editor): Tagungsberichte Zerstörungsfreie Prüfung im Bauwesen (Proceedings NDT-CE), Berlin 1985 + Berlin 1991, DGZfP, Berlin
/ L108/	Schickert, G., Krause, M. Wiggenhauser, H.: ZfPBau-Kompendium (NDT-CE Compendium), BAM Vol. 177, Berlin (1991)