A multi-electrode measurement system for steel fiber reinforced concrete materials monitoring

Steel fiber reinforced concrete structural elements represent very interesting materials which employment has led to tangible advantages in construction technologies over the last decades. The behaviour of this kind of materials is strictly related to the fiber dispersion inside the cementitious matrix. For this reason, in the last years different non destructive measurement methods have been proposed, in order to monitor the fiber reinforced concrete structural elements, and in particular to detect the fiber orientation and clumping. The most part of them are based on an AC-impedance spectrometry that requires measuring the electrical impedance of a specimen of the material over a wide frequency range (from few milliherz to some megahertz). Even though the proposed methods are fairly effective, their practical implementation is manly restricted to laboratory tests, since they require both critical measurement setups and ad-hoc specimens. In this paper a different approach to the monitoring of fiber reinforced material is presented. It is still based on the AC-impedance spectrometry, but the frequency range of interest is limited from some hundred hertz to a few dozen of kilohertz. This choice strongly relaxes the aspects related to the size of the electrodes and their coupling with the material under test. So that it is possible to perform the monitoring using electrodes placed on the surface of the material. It is even possible to employ a multi-electrode probe that permits to analyze a large portion of the material simultaneously. Moreover, it can be adopted not only for laboratory tests, but also for the monitoring of element yet carried out (e.g. pavements, industrial floors, wall panels, et)