# Non-Destructive Multi-Method Assessment of Steel Fiber Orientation in Concrete +
## 3 Results
### Spectral Induced Polarization  
The SIP data collected on all five cylindrical samples listed in Table 1 and the measured real and imaginary electrical conductivities along with the amplitude and phase spectra are plotted in Figure 8. Though all samples were measured in a dry state (meaning that there is no significant pore fluid and electrical conductivity was not possible due to ion  
Figure 6: Ultrasonic measuring system: block diagram (**left**), photo of the measurement set-up (**centre**) and close-up, of the ultrasonic probes (**right**). In the close-up the polarization \(\bar{P}\) of the transmitters is shown in red.  
movement), we measured relatively low electrical resistivities between 10 and 800 Ohm*m (Figure 8, left). Most of the samples, besides Q0F which does not contain steel fibers, moreover showed distinct polarization behaviour with absolute phase values well above 20 mrad. As could be expected, the sample Q80 || || showed, due to its high fiber content, the lowest resistivity magnitude and highest polarizability. These characteristics were less pronounced for the three samples with 40 kg/m\({}^{3}\) fiber content. When comparing the results of these latter three samples, Q40 || ||, where the steel fibers are oriented along the sample axis (and along the electrically induced current flow within the SIP sample holder), features the lowest electrical resistivity amplitude. For the sample Q40*, where the steel fibers are randomly distributed, the electrical resistivity increases and for sample Q40--, where steel fibers are oriented perpendicularly to the induced current flow, we measure the highest resistivity values for a sample containing fibers. Furthermore, from their electrical polarization behavior, these three samples can clearly be differentiated. The sample Q40 || || Cylinder is most polarizable, with up to \(-400\) mrad. When the steel fibers are randomly distributed (i.e., Q40* Cylinder), the electrical polarizability decreases to about \(-350\) mrad and when the fibers are perpendicular to the sample axis (and induced electrical field) (i.e., Q40--Cylinder), the polarizability becomes less than \(-50\) mrad.  
Figure 7: Spherical coordinate system, reproduced from [PERSON] et al. 2018 under the terms of the Creative Commons Attribution 4.0 International License ([[https://creativeccommons.org/licenses/by/4.0/](https://creativeccommons.org/licenses/by/4.0/)]([https://creativeccommons.org/licenses/by/4.0/](https://creativeccommons.org/licenses/by/4.0/)), accessed on 28 November 2021), (**top left**) ). Fiber renderings and orientation histograms for sample Q0F Cylinder (**top centre**), Q80 || || Cylinder (**top right**), Q40—Cylinder (**bottom left**), Q40 || || Cylinder (**bottom centre**), Q40* Cylinder (**bottom right**). Histogram radius: \(0<\Phi<90^{\circ}\); histogram circumference: \(0<\Theta<360^{\circ}\).  
Given that the concrete mix and the dosage of steel fibers within these three samples was constant, we can assume that the observed differences in the electrical resistivity behavior are due to the fiber orientation. Thus, we can observe, for instance, that the position of the phase peak slightly shifts towards higher frequencies with increasing amount of steel fibers tilted away from the direction of the induced electrical current flow (which coincides with the long axis of the cylindrical samples).