## 4 Concluding Remarks  
In this paper, we investigate the feasibility and working mechanisms of a novel solution for monitoring concrete structures based on a wireless electrical resistivity sensor. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Region** & **Number of Slices** & \begin{tabular}{c} **Core Volume per** \\ **Region (\(\upmu\)m\({}^{3}\))** \\ \end{tabular} & \
\begin{tabular}{c} **Total Volume of Air Voids** \\ **per Region (\(\upmu\)m\({}^{3}\))** \\ \end{tabular} &
\begin{tabular}{c} **Air Voids/Volume of** \\ **Region (\(\upmu\)m\({}^{3}\))** \\ \end{tabular} \\ \hline R1 & 1520 & \(1.42\times 10^{21}\) & \(1.77\times 10^{13}\) & \(1.25\times 10^{-8}\) \\ R2 & 1204 & \(1.12\times 10^{21}\) & \(1.60\times 10^{13}\) & \(1.42\times 10^{-8}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Quantification of air voids volume per region based on the X-ray CT data. Figure 16: Three-dimensional volumes of the concrete core divided into regions: (**A**) original volume; (**B**) segmented air voids and housing device; (**C**) filtered air voids; and (**D**) isolated air voids. UGCT CoreTOM (180 kV, 90 W, exp. 650 ms, 90 \(\upmu\)m voxel size). Figure 17: Size distribution of the individual air voids by volume. As an alternative to current commercial solutions, this system has the added features of large-range wireless data transmission and simultaneous recording of electrical resistivity on different depths of the concrete cover. The research covered the determination of the dielectric properties of concrete under semi-realistic curing conditions as well as accelerated degradation conditions, the data transmission and antenna range in the wireless communication of the sensor device embedded in real structures, and the effects of the hardware on properties of the concrete such as compressive strength and distribution of concrete/presence of air voids in the proximity of the devices. In summary, the following conclusions could be drawn from the study:  
* The permittivity of concrete does not change during its lifetime after it has dried out, not even under accelerated degradation conditions (accelerated carbonation). Thus, the communication link will not be influenced by the concrete life cycle, which will reduce the robustness requirement during the antenna design stage. * There was no interference of the reinforcement steel bars on the in-to-out transmission of concrete antenna communication and a long-range communication link from in-to-out concrete to an LTE cell tower was achieved. Thus, wireless communication will not limit the use of this system for any concrete application. * The sensors and whole hardware device performed in a stable and reliable way during data collection and transmission in the pilot study for the two cement types used under realistic conditions, which means that the system could be used for many applications within the concrete industry (different cement types and different environmental conditions). * The presence of the hardware device did not promote a poor distribution of the concrete in the areas close to the sensor, and no increased air void or poor adherence between the concrete and the device were found. This proves that the use of the system will not significantly interfere with the properties of the concrete structure. Conceptualization, J.R.T.F. ; methodology, J.R.T.F., J.G., R.A., Y.A. and D.E.V.M. ; formal analysis, J.R.T.F., J.G., R.A., Y.A. and D.E.V.M. ; investigation, J.R.T.F., J.G., R.A., Y.A. and D.E.V.M. ; writing--original draft preparation, J.R.T.F., J.G., R.A., Y.A. and D.E.V.M. ; writing--review and editing, J.R.T.F., J.G., R.A., Y.A., D.E.V.M., G.V. and D.P. ; supervision, G.V., V.C., D.P. and S.M. ; project administration, D.P. ; funding acquisition, D.P. and S.M. All authors have read and agreed to the published version of the manuscript. This work was executed within the imec.icon project CoMModore, a research project bringing together academic researchers and industry partners.