The maintenance of existing concrete structures gains increasing importance. New challenges within this topic are the durability modelling of conservation measures and the timing of renewing them. One necessary step for the solution of these new challenges are needs-oriented non-destructive testing methods. For the first time, ever, a mobile nuclear magnetic resonance (NMR) sensor allows a non-destructive determination of relevant parameters directly on the building site. By positioning the NMR sensor on a lift analysing of the amplitudes and relaxation times can be done at different depths/positions inside the concrete cover.
The determined parameters are: Ingress, distribution and transport of water as well as other liquids at the concrete surface (up to 25 mm depth beginning at the concrete surface) and effectiveness of concrete coatings including thickness of different coating layers.
However, before this technique can be used on steel-reinforced concrete elements, the potential effect of the reinforcement on the measurement, i.e. the NMR signal, needs to be studied. This has been done in the frame of a wide test program. Firstly, influences from temperature changes and tilting of the sensor are discussed in the present paper. Afterwards results concerning the steel reinforcement influence on the investigations are named and a practical solution to consider the determined shift of the profile towards the steel is presented.
Orlowsky, J. (2017). Performance of Mobile NMR for Non-destructive Analyses of Existing Concrete Structures – Influencing Factors. High Tech Concrete: Where Technology and Engineering Meet, 1299–1306. https://link.springer.com/chapter/10.1007/978-3-319-59471-2_150