## 3 Results
### Mechanical Properties
In addition, it can be observed that for this property, the incorporation of reinforcement fibers does not result in an improvement in strength. In other studies, improvements were only obtained for flexural strength, even reducing the compressive strength as a consequence of the addition of fibers [95]. In view of the results obtained, a potential application of these cement mortars would be in masonry works where the mechanical requirements need not be very high [96]. However, it is important to take into consideration the compatibility between the mortar and the ceramic pieces in order to avoid excessively stiffening the wall [97]. In this sense, other potential applications for this type of mortar according to the literature are the production of prefabricated elements, floor slabs or urban furniture, among others [98,99]. Finally, to complete the discussion of the mechanical results, SEM images have been included to show the microstructure of the mortars produced in this research. The results are presented in Figure 9. It should be noted that these images were obtained with the aim of capturing as much information as possible and thus providing a complementary discussion of the mechanical properties analyzed. For this reason, the magnifications were selected for each mortar according to the diameter of the natural fiber added and the characteristics of the mortars studied. Figure 8: Compressive strength results. Regarding mortars made with coconut fiber, a slight cracking of the matrix around the fibers can be observed in Figure 9a. This weakening may be due to the absorption of hydration water from the cement by the fiber during the hardening process. Also, although fiber dispersion was good, there are preferential points of fiber accumulation. Figure 9b shows in detail the interface between coconut fiber and the cementitious matrix, where the good adhesion between the two and the formation of compounds derived from the hydration of the cement on its surface can be seen. It is well known that the arrangement of strong, stiff, and brittle fibers, as well as a higher strength of the fiber-matrix bond, results in better mechanical properties and reduced ductility [25]. Figure 9c shows the integration of abaca fiber into the cement mortar matrix. As highlighted by some authors [100], the bonding between added fibers and mortar matrix is directly linked to the lignin and cellulose content of these natural reinforcement materials. These biopolymers are shown in Figure 9d, showing one of these fibers in detail. In general, natural fibers exhibit a bridging effect similar to that of existing synthetic fibers, which can reduce autogenous shrinkage by connecting the micro-cracks in the matrix and inhibiting the propagation of cracks at an early stage [36]. Finally, Figure 9e shows in detail the interior of the toquilla straw fiber where its composition can be seen. These larger diameter fibers were the ones that, to a lesser extent increased the flexural strength of the mortars made with RCA. Although it is true that, as seen in Figure 9f, there is a good integration between the reinforcement and the matrix. However, it can be seen how toquilla straw fiber broke after the flexural test, as illustrated in the SEM image obtained.