## 2 Materials and Methods  
### Mortar Formulation and Manufacturing  
Five different binders were considered in this study. Four hybrid mortars of ecological interest using slag and a Type I PC as precursors. A plain PC mortar (based on Type II/B-M PC, according to UNE-EN 197 standard) was also manufactured as commercial reference. Type I PC is considered a general, all-purpose cement, with \(>\)95% of linker in its composition, thus being adequate for hybrid mortars to ensure reactivity. Type II/B-M cement was selected to manufacture the reference mortar, due to its high level of implantation in construction. Type II/B-M cement presents 65-79% of linker in its composition, with the remaining portion consisting of other main constituents like limestone, fly ash, or blast furnace slag, and minor constituents like gypsum. Table 1 shows the chemical composition of these three materials, determined by X-ray fluorescence (XRF). The results for the particle size of the precursors used to manufacture the binders are summarized in Table 2.  
For the formulation of the hybrid mortars, two different types of activators were used, both of them in two amounts that involve two similar Na contents: 0.05 and 0.10 moles of Na per 100 g of binder. Na\({}_{2}\)CO\({}_{3}\) (3% and 6% by weight, from Panreac) and NaNO\({}_{3}\) (4% and 8% by weight, from Labkem) were added to obtain those Na moles, with lower values yielding 0.05 moles of Na and the higher ones yielding 0.10 moles of Na, always per  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Composition (\% by Weight)**} \\ \hline  & **MgO** & **Al\({}_{2}\)O\({}_{3}\)** & **SiO\({}_{2}\)** & **SO\({}_{3}\)** & **K\({}_{2}\)O** & **CaO** & **TiO\({}_{2}\)** & **Fe\({}_{2}\)O\({}_{3}\)** \\ \hline Type I PC & 1.3 & 4.7 & 17.8 & 4.6 & 1.4 & 67.3 & 0.2 & 2.6 \\ Type II/B-M PC & 2.2 & 6.2 & 19.4 & 4.1 & 1.6 & 61.7 & 0.8 & 4.0 \\ Slag & 10.9 & 10.3 & 31.9 & 1.4 & 0.5 & 44.1 & 0.6 & 0.3 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Chemical composition of the precursors used for manufacturing the binders under study determined by XRF.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Particle Size (\(\mu\)m)** \\ \hline  & **d10** & **d50** & **d90** \\ \hline Type I PC & 3.2 & 15.9 & 40.7 \\ Type II/B-M PC & 3.5 & 14.1 & 43.0 \\ Slag & 3.7 & 11.2 & 28.5 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Particle size of the precursors used for the manufacture of the binders, determined by dynamic light scattering.  
100 g of binder. The two Na concentrations selected for both salts correspond to the range of those considered in previous studies using sulfates [42]. The Na/Ca ratio, an important factor for the further development of the hydration reactions, is also detailed in Table 3. The solid activator was introduced in powdered form and thoroughly homogenized with the slag and cement during the dry mixing stage. Subsequently, the required volume of water was incorporated into the dry blend to achieve the final mortar mixture.  
The labels chosen for the five mortars considered in the present study, and used hereafter in the article, can be seen in Table 3, together with their dosages. For the mortar manufacturing, standardized sand (according to EN 196-1 standard) was added in the usual sand/binder (\(s/b\)) ratio of \(3/1\). The amount of water for the mortars was determined following the criterion of similar work abilities (which were measured according to the EN 196-3 standard).  
Carbonate-activated hybrids (HC), nitrate-activated hybrids (HN) and commercial Portland cement (OPC) mortars were used for manufacturing the different types of samples for the experimental studies detailed in Section 2.2 formulations in Table 3. All the samples were cured for 28 days in a chamber at 99% relative humidity (RH) and 25 \({}^{\circ}\)C.