## 4 Conclusions  
The aim of this experimental research was to analyze the effect of the TiO\({}_{2}\) nanoparticles content in white Portland cement-based cementitious matrix regarding the surface hydrophilicity by the means of surface water absorption as a relevant parameter for the hydrophilicity characteristics of materials under several exposure conditions (water amount reaching the considered surface, exposure to UV rays).  
Experimental results show that the hydrophilicity of the cementitious composite surface is not directly influenced by the content of nanoparticles and there is a concentration range in which they develop maximum efficiency. In this case it was proved that an addition of TiO\({}_{2}\) nanoparticles (relative to the cement quantity) in the range of 3%-6% is the optimum in terms of kinetics and phenomenon efficiency. Based on the above obtained results, current conclusions are consistent with the existing literature in the field in terms of mechanisms that affect the general self-cleaning capacity of the cementitious composites with nano-TiO\({}_{2}\) in terms of surface hydrophilicity. An increased addition of TiO\({}_{2}\) nanoparticles (see sample P9 with 10% TiO\({}_{2}\) nanoparticles) not only does not improve surface performance in terms of hydrophilicity, but on the contrary, it reduces it.  
By analyzing the overall evolution of the surface water absorption results of the cementitious composite samples, it can be said that the P8 (6% TiO\({}_{2}\)) sample is the most balanced and has the most successful outcome regarding the evolution of the phenomenon, the kinetics of the process of water absorption, and the effectiveness of the presence of the nanoparticles in comparison to the control sample.  
After analyzing the literature, it can be said that the current experimental research originally contributes and adds value to the current level of knowledge. This is done by the identification of suitable functions for the modeling of the phenomena and the kinetics of the latter by introducing and demonstrating proper use of relevant indicators for the efficiency of the process. The results of the current experimental study and their analysis facilitate the proper comparison and interpretation of a large volume of experimental data collected considering different, relevant exposure situations.  
Last but not least, based on the specific results obtained, on a case-by-case basis it is necessary to analyze the optimal amount of nanoparticles used as an addition in the cementitious matrix that can optimize the quality of the self-cleaning process, depending on the use, climate, degree and duration of sunlight.  
Figure 6: Surface water absorption: unexposed UV test specimens (0 UV); 1 H UV exposed test specimens (1 UV) and 1 + 24 h UV exposed test specimens (24 UV).  
**Author Contributions:** Conceptualization, A.H. and E.G.; methodology, A.H., E.G., H.S., A.-V.L.; formal analysis, A.H., E.G., H.S., C.R.; investigation, A.H., E.G., H.S., A.-V.L.; writing--original draft preparation, A.H., E.G., A.V.S., C.R.; writing--review and editing, A.H., E.G., H.S., A.V.S., A.-V.L., C.R.; visualization, A.H., E.G., H.S., A.-V.L.; supervision, A.V.S., H.S. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Acknowledgments:** Authors would like to thank Evonik Industries AG Hanau, Germany, for providing the necessary materials used in the current study.  
**Conflicts of Interest:** The authors declare no conflict of interest.