Application of mobile NMR to characterise building materials
Jeanette Orlowsky, TU Dortmund, Dortmund, DeutschlandUdo Antons, TU Dortmund, Dortmund, Deutschland
Nuclear magnetic resonance (NMR) is a method to assess material properties by stimulating a response of the atomic nuclei using magnetic fields and radio-frequency irradiation. In contrast to conventional NMR spectroscopy, which uses highly homogeneous magnetic fields, the method used here relies on inhomogeneous magnetic fields applied from a single side. The advantage of single-sided NMR is the virtually unlimited sample size as well as the potential to construct mobile devices that can eventually be used on construction sites.
A compact unilateral sensor developed for non-destructive testing of materials containing hydrogen atoms, the so-called NMR MOUSE (Mobile Universal Surface Explorer) was used for the described work. Different types of the NMR MOUSE are available. The types differ in terms of frequency, gradient, measuring depth and resolution. For the described investigations the NMR MOUSE PM 5 and PM 25 with measuring depth of 5 respectively 25 mm was used. The PM 5 has a measuring field of 20 by 20 mm in the cross-section and the thickness can be chosen between 10 and 100 µm (volume of measurement = sensitive volume) while the PM 25 reach a resolution of 100 µm (= thickness of the sensitive volume).
After shortly describing the test methodm the contribution focusses on three different particular case studies in the field of building materials:
a) Investigating polymeric concrete coatings concerning the thickness of different coating layers, material changes due to weathering and changes of water content inside the coating as well as in the concrete.
b) Analysing the ingress and reaction of hydrophobic agents in concrete.
c) Determination of the water content and water mobility inside the concrete.
The report concludes by discussing potential effects on the measuring method like the steel reinforcement inside the concrete.