## 2 Materials and Methods
### Materials
#### 2.1.2 Aggregates  
In this research work, two types of aggregates were used for the manufacture of mortars: natural sand and recycled sand from concrete waste. Table 2 shows the results derived from the physical characterization of the aggregates following the guidelines of the UNE-EN 13139:2002 standard [46]. To determine these properties, aggregate fractions between 4000 and 0.063 mm were used, with the exception of fines content and fineness modulus, where particle sizes between the 4000 mm sieve series and the bottom were used. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**CaO** & **SiO2** & **SO3** & **Al2O3** & **Fe2O3** & **K2O** & **TiO2** & **MgO** & **SrO** & **BaO** & **MnO** & **P2O5** \\ \hline
69.80 & 17.05 & 4.21 & 4.10 & 3.45 & 0.66 & 0.24 & 0.23 & 0.08 & 0.07 & 0.07 & 0.04 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Percentage chemical composition of cement type CEM II/B-L-32.5 N. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Test** & **Fine Content** & **Particle** & **Fineness** & **Fiability** & **Bulk. Dens,** & **Dry Dens.** & **Water Absorption** \\  & **(\%)** & **Form** & **Modulus (\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%/m3)** & **(\%)** \\ \hline
**Norma** & **UNE EN** & **UNE-EN** & **UNE-EN** & **UNE-EN** & **UNE-EN** & **UNE-EN** & **UNE-EN** & **UNE-EN** 1097-6** \\  & **933-1**[47] & **13139**[46] & **13139**[46] & **146404**[48] & **1097-3**[49] & **1097-6**[50] & **1097-6**[50] \\ \hline NA & 1.97 & - & 4.35 & 21.12 & 1581 & 2509 & 0.91 \\ RA-Con & 3.73 & Not relevant & 4.08 & 23.17 & 1328 & 2246 & 7.06 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Physical characterization of the aggregates used. Figure 1: Materials used. **(a)** Cement type CEM II/B-L-32.5; **(b)** natural aggregate (NA); **(c)** recycled concrete aggregate (RA-Con); **(d)** aramid fiber; **(e)** Glenium Sky 604 superplasticizer. As can be seen from the analysis of Table 2, recycled concrete aggregates have a higher fines content than natural aggregates as a result of the crushing and grinding process carried out during their manufacture [51]. On the other hand, it can be seen how the density of the natural aggregate is higher than in the recycled aggregate, which will result in higher mechanical strengths for natural sands [52]. Finally, it should be noted that recycled concrete aggregate has a water absorption coefficient seven times higher than natural aggregate, this has a negative impact through the demand for a greater amount of mixing water in the manufacture of masonry mortars [53]. Figure 2 shows the particle size curves obtained for the aggregates used. A continuous particle size for the sands makes it possible to obtain more homogeneous and workable mortar mixtures [54]. For this reason, the particle size was determined using a series of standardized metallic sieves according to UNE-EN 9332 [55], whose mesh spans are between 4.000 and 0.063 mm. On the other hand, a chemical characterization of the recycled aggregates was carried out to better understand their composition. First of all, a gravimetric thermal analysis was carried out with the aid of an SDT Q600 analyzer, thanks to which it was determined that the calcite content of the recycled concrete aggregates used was 17.55% and the gypsum particle content was 4.24%. These percentages should be taken into consideration in case the mortars come into contact with steel materials, since a high content of sulfur compounds can accelerate their deterioration [57]. Finally, the elemental chemical composition of the recycled aggregates was analyzed using the X-ray fluorescence (XRF) technique. The results of this analysis are shown in Table 3.  
From the chemical analysis presented in Table 3, the high SiO\({}_{2}\) content of the recycled concrete aggregates can be highlighted, as a consequence of the natural aggregates used in the manufacture of the concrete [58].