# Photocatalytic Recycled Mortars: Circular Economy as a Solution for Decontamination
## 5 Conclusions  
This research produced mortars with decontaminating capacity by introducing waste into the productive cycle and contributed to the implementation of the circular economy model. The results show suitable mechanical behavior despite the incorporation of recycled aggregates, since total replacement of NS by RS meant a decrease in compressive and flexural strength of only approximately 18%, with average values of 46 MPa and 13 MPa, respectively. The strength obtained with photocatalytic cement was slightly higher compared to its counterpart made with traditional cement. The properties of water absorption by capillarity, water absorption capacity, and open porosity showed a slight increase for 40% and 100% RS, while in the results obtained for 20% RS, the values obtained were very similar to those of the reference mortar. The bulk and skeletal density showed very similar values in the two families and for all replacement ratios.  
The penetration of CO\({}_{2}\) obtained in the carbonation test carried out showed a clear benefit with the incorporation of recycled sand. This could be a positive aspect, as it reduces the carbon footprint in the environment.  
From a photocatalytic point of view, the incorporation of up to 40% RS slightly favored the elimination of NO\({}_{x}\), but the mortar with 100% RS had a significant increase relative to the conventional mortar, moving to a better classification (category 2). These mortars were more porous than conventional mortars, facilitating the entry of light into the interior and, consequently, the elimination of polluting gases. The results obtained add value to the use of recycled aggregates, clearing up the uncertainties that still exist in the use of this material.  
Therefore, a photocatalytic mortar with 100% mixed recycled sand is proposed in order to produce the greatest environmental benefits, due to the greater absorption of CO\({}_{2}\) and NO\({}_{x}\) and the greater use of recycled aggregates. Also, the strength is slightly lower but compatible with its use in low-requirement applications in contact with the atmosphere, such as pavement blocks or cladding mortar.  
The findings of the present study prove that reducing natural sand mining, minimizing energy consumption and CO\({}_{2}\) emissions, reducing global warming, preventing illegal deposition and landfilling of the fine fraction of CDW, and complying with the limits of the European Waste Framework Directive are possible in order to achieve and promote cleaner production in the construction sector (eco-efficiency).  
Figure 9: Elimination of NO\({}_{x}\) (%).  
Future lines of research are intended to improve the photocatalytic capacity of mortars based on the good mechanical behavior of the mortars studied in this research by studying the influence of the content and origin of fine aggregates, different aggregates and their nature, reducing the amount of cement due to the good mechanical behavior obtained, or increasing the amount of water according to the percentage of increased RS, or pre-saturating it.  
Conceptualization, A.B., A.L.-L., and J.A.; Methodology, A.B. and A.L.-L.; Software and validation, A.B. and A.L.-L.; Formal analysis, A.P.G.; Investigation, A.L.-U. and A.P.G.; Data curation, A.B. and A.L.-L.; Writing--original draft preparation, A.B. and A.L.-L.; Writing--review and editing, A.B., A.L.-L., and J.A.; Visualization, A.L.-U. and A.P.G.; Supervision, A.B., A.L.-L., and J.A.; Funding acquisition, J.A.. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The authors declare no conflict of interest.