## 4 Conclusions  
This research has addressed the development and physico-mechanical characterization of cement mortars made with RCA and reinforced with three types of natural fibers. Thus, this research contributes to progress towards the circularity of construction products and the characterization of new materials produced under circular economy criteria. The main conclusions of this study are:  
* Mortars made with RCA have a lower bulk density than those made with natural aggregate. This decrease in density of close to 10% is even greater for those samples made with natural fibers. Thus, this lower density and the incorporation of fibers of vegetable origin have a positive effect on the thermal conductivity of the mortars. For the best case, with the incorporation of toquilla straw fibers, the RCA-1:3-1.5%(T) dosage obtained a thermal conductivity 37% lower than that of the reference mortar (NA-1:3). * Capillary water absorption was much higher in those mortars made with RCA due to the nature of these sands. However, the incorporation of natural fibers managed to reduce the capillary water absorption, although without reaching the values obtained for the traditional mortar made with natural sand. * The incorporation of natural fibers reduces shrinkage during the drying of mortars made with RCA, thus approaching the behavior experienced by traditional mortars. It has been observed that the mortars made with abaca fiber showed greater dimensional stability. * Surface hardness was not affected by the type of aggregate used in the manufacture of the mortars, although it was slightly reduced by the incorporation of natural fibers. * The production of mortars with RCA has a negative impact on bond strength. Thus, the adhesion of traditional mortar is superior to mortar with RCA and, in turn, the incorporation of natural fibers has an impact on the decrease in this mechanical property. Mortars with higher cement content showed higher bond strength. * Flexural strength of mortars made with recycled aggregate is lower than that of traditional mortar and is reduced as the cement content in the mix decreases. Despite this, the incorporation of natural fibers has a positive impact on the improvement of the flexural strength of mortars made with RCA, with coconut and abaca fibers showing the best performance. * The incorporation of fibers did not significantly improve the compressive strength of the mortars, the type of aggregate being the determining factor for this property. Thus, the traditional mortars showed a higher compressive strength than their counterparts made with RCA. This study's limitations and future lines of research include the need to carry out accelerated ageing tests, which would make it possible to estimate the durability of these mortars. In the same way, for its use as a facing material, it would be convenient to analyze the optimum fiber length that allows an improvement in the mechanical properties, without excessively reducing the workability of the mortar. Finally, its application in the development of blocks or prefabricated pieces would be interesting for the future industrialization of these products. Moreover, taking into account the availability of natural fibers whose impact was examined in this study, i.e., abaca, coconut, and toquilla straw, and that the most beneficial use of these natural raw materials in terms of environmental impact will be in their place of origin, the results of this study are also an indication for professionals involved in construction in areas where these natural fibers occur. The research described in this article fits well with the expectation that recycling and reuse of demolition materials and usingrenewable raw materials are/will be a traditional and common practice in the construction sector, bringing us closer to sustainable development. Conceptualization, D.F. and A.Z.-B. ; methodology, A.Z.-B. and D.F. ; software, A.Z.-B. and R.P.L. ; validation, D.F., P.S. and J.M. ; formal analysis, D.F. and R.P.L. ; investigation, A.Z.-B., D.F. and R.P.L.