## 3 Results and Discussion
### Evolution of the Dynamic Young's Modulus over Time
In all cases, the resistance to adhesion was higher than the 0.30 N/mm\({}^{2}\) required by the UNE-EN 998-1: 2018 standard [57]. The surface hardness measured in Shore D units was also reduced in mortars made from the recycled aggregate. Furthermore, in Table 7, it can be seen that the absorption of water by capillarity, which depends directly on the porosity of the material, was higher in mortars made with recycled aggregate, especially in those dosages with a cement/aggregate ratio of 1:4. This higher absorption rate can cause problems if this type of material is placed outdoors and exposed to frequent rainfall, as in the case of efflorescence or humidity. In any case, the mortars made with recycled ceramic aggregate had higher absorption values. Finally, it was verified that a greater compactness with a cement/aggregate ratio of 1:3 favored higher real-density values. As in the other properties, mortars made with natural aggregate had higher frequencies than their counterparts made with recycled aggregates. Figures 9 and 10 show the results derived from the evolution of the dynamic Young's modulus and its relationship with the most relevant mechanical properties of masonry mortars--flexural strength and compression. For this, tests were carried out on test tubes from the same mix at ages 7, 14, 28, 56 and 72 days for each of the dosages studied and in a laboratory environment (cured in a humid chamber at 20 \({}^{\circ}\)C and 80% relative humidity). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Type** & **Equation** & **R\({}^{2}\)** & **Type** & **Equation** & **R\({}^{2}\)** \\ \hline MY–NA—1:3 & y = 0.9131x + 228.47 & 0.9758 & MY–NA—1:4 & y = 0.8710x + 426.61 & 0.9925 \\ \hline MY–ARH—1:3 & y = 0.8515x + 441.91 & 0.9836 & MY–ARH—1:4 & y = 0.7360x + 808.94 & 0.9952 \\ \hline MY–ARC—1:3 & y = 0.8255x + 527.14 & 0.9976 & MY–ARC—1:4 & y = 0.7738x + 694.43 & 0.9819 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Linear regression adjustments and R\({}^{2}\) coefficients for the relationship of speed measurements obtained by ultrasound and by the Arduino system. As is known, mortar acts as a resistant connection element in most applications. It is capable of transmitting the stresses of the construction system of which it is a part and distributing the loads acting on it. In the analysis of Figures 9 and 10, an increase in the mechanical resistance of flexion and compression is observed as the time since mixing increases. In this sense, a rapid growth of resistance at an early age is observed, which stabilizes after 56 days. In the same graphs, the progress of the dynamic Young's modulus is been represented with a dashed line, indicating the values obtained at the suggested ages. Regarding mechanical properties, the better performance of mortars made with natural aggregate can be seen, with mortars made with recycled ceramic aggregate having the lowest strength. Besides, as was the case with other physical properties presented in Table 7, the highest dosages in cement with a 1:3 ratio showed higher flexural and compressive strength values than their counterparts with a cement/aggregate ratio of 1:4. Regarding the compressive strength, in all the mixes tested, the minimum resistant classification M of 7.5 MPa for mortars with application in plasters and plasters established by the UNE-EN 998-1: 2018 standard [57] was exceeded. Furthermore, following other studies exploring how the dynamic Young's modulus evolves rapidly at an early age and later  
Figure 10: The evolution of the compressive strength (bars) and dynamic Young’s modulus (dotted lines) measured over time for the different dosages used. Figure 9: The evolution of the flexural strength (bars) and dynamic Young’s Modulus (dotted lines) measured over time for the different dosages used. begins to stabilize, the variations produced in this property were proportional to those observed in the evolution of static mechanical resistance [58].