# Non-Destructive Multi-Method Assessment of Steel Fiber Orientation in Concrete +
## 5 Conclusions  
SFRC is still a relatively new building material, which holds great potential for innovative use and design approaches for future concrete structures. The assessment of SFRC properties, such as fiber orientation and dosage, is still difficult, often requiring coring and elaborate lab analysis. Our study focusses on the effectiveness of alternative methods to extract this information non-destructively.  
Evaluating the electrical behavior of SFRC samples, we found that both the resistivity magnitude and phase (i.e., the material's capability to polarize) are sensitive to the main fiber orientation. It is conceivable that when both are measured, fiber orientation and content can be assessed. Likewise, for the measured samples we saw that the transmission amplitude of ultrasonic shear waves is slightly diminished and that higher frequency components are attenuated when the polarization of the wave is parallel to the fibers' direction. However, the dimensions of the test specimens have the same order of magnitude as the ultrasound wavelength itself. This results in reflections of the ultrasonic waves from the test body sides and a superposition of different wave modes in the received signal, making the interpretation of the results difficult. In addition, variations in probe coupling have an influence on the received signals. For this reason, further ultrasonic measurements are necessary, using a larger number of test specimens with bigger dimensions, to further investigate these first indications of an influence of the fibres on the ultrasonic signals.  
The X-ray CT analysis provided quantitative measurements of fiber orientation as well as visualizations of actual fiber distributions within the specimens. These measurements not only verified the successfulness of the specimen casting technique in producing specimens with controlled fiber orientations. They also can serve as a quantitative basis for assessing correlations between ultrasonic or SIP measurements and actual fiber conditions. An analysis of the statistical correlation between the quantitative fiber orientation data measured using X-ray CT and the phase variations measured using SIP could yield useful mathematical relationships that could be utilized as a basis for expanding fiber orientation assessment using SIP to further applications (such as measurement of larger components or of different fiber types). Such a statistical analysis is the planned topic of the authors' future work in this area.  
Conceptualization, S.K., T.O. and P.S.; methodology, all; validation, T.O., D.M., F.M. and S.K.; investigation, T.O., D.M., F.M. and S.K.; resources, P.S.; data curation, T.O., D.M., F.M. and S.K.; writing--original draft preparation, all; writing--review and editing, all; visualization, all; supervision, S.K., T.O. and P.S.; project administration, all. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
**Acknowledgments:** The authors express their gratitude to company SV Bekaert SA for the provision of steel fibers as material used in this investigation, and the valuable scientific feedback. Moreover, we thank [PERSON] and [PERSON] from BAM for technical support and sample preparation. The opinions expressed in this publication are those of the authors and they do not purport to reflect opinions or views of the supporting organisations.  
**Conflicts of Interest:** The authors declare no conflict of interest.