## 2 Materials and Methods
### Mortar Characterization  
For monitoring the dimensional changes that can occur during the mortar curing process, and during the drying that takes place during the subsequent exposure to the atmosphere, four samples of 285 \(\times\) 25 \(\times\) 25 mm size from each of the five mortars under study were manufactured. All of them were monitored during their curing at 99% RH and 25 \({}^{\circ}\)C, and then during their drying in conditions that simulate continental environments (40% RH and 25 \({}^{\circ}\)C). The monitoring of the dimensional changes during drying was also carried out for 28 additional days. Length changes were evaluated following the procedure described in the UNE-EN 80, 112 standard. A K02 length comparer from Shock Baker, with \(\pm\)0.002 mm accuracy, was used for these studies. For each mortar formulation, six prismatic mortar samples, 160 \(\times\) 40 \(\times\) 40 mm in size, were also manufactured to carry out the mechanical and microstructural characterization. Different characterization studies related to the chemical composition of the mortars such as pH and oxidation profile measurements and simultaneous differential thermal analysis (DTA) and thermogravimetry measurements (TG) were also carried out on samples obtained from this type of specimens. For mortars under both conditions (cured and dried), open porosity was measured comparing helium pycnometry (apparent density), using an Accupyc 1330 helium pycnometer (Micromerities, Norcross, GA, USA), and Archimedes technique (following UNE-EN 993-1 standard). A helium pycnometer allows the density of the material and the volume of closed pores (those the He is not able to penetrate) to be determined. Cubes (approximately 1 \(\times\) 1 \(\times\) 1 cm) obtained from the central region of each mortar were used for these measurements. Each measurement was performed in triplicate, and epoxy resin \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Label** & **Precursors** & **Activator** & **Na/Ca mol Ratio** & **Workability (cm)** & _w/b_ & _s/b_ \\ \hline OPC & 100\% Type II/B-M PC & — & — & 17.0 \(\pm\) 0.1 & 0.50 & \\ HC-3\% & 78.5\% slag + 18.5\% Type I PC & 3\% Na\({}_{2}\)CO\({}_{3}\) & 0.06 & 16.5 \(\pm\) 0.1 & 0.47 & \\ HC-6\% & 77\% slag + 17\% Type I PC & 6\% Na\({}_{2}\)CO\({}_{3}\) & 0.12 & 16.6 \(\pm\) 0.1 & 0.47 & \(3/1\) \\ HN-4\% & 78\% slag + 18\% Type I PC & 4\% NaNO\({}_{3}\) & 0.06 & 16.8 \(\pm\) 0.1 & 0.45 & \\ HN-8\% & 76\% slag + 16\% Type I PC & 8\% NaNO\({}_{3}\) & 0.13 & 18.9 \(\pm\) 0.1 & 0.45 & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Dosage and workability of the mortars under study. (Macdermid Enthone, Birmingham, UK) was used to seal the samples for the Archimedes method. Hence, open porosity (to He) was determined combining both methods. The overall porosity and pore size distribution of the mortars after drying were assessed using Hg intrusion porosimetry utilizing a Micrometrics Autopore IV 9500 analyzer (Micromerities, Norcross, GA, USA). This investigation was conducted with a multiplicity of three. Upon the completion of the curing and drying period, the specimens were analyzed using scanning electron microscopy (SEM), specifically the FEI Teneo model, to investigate potential microstructural changes, including the occurrence of microcracks. After 28 days of curing and 28 days of drying, three specimens of each mortar were subjected to compression tests, in accordance with the EN 196-1 standard, using EM2 (Microtest, Madrid, Spain) universal testing machine. Moreover, the oxidation front was measured in the split mortars. The valuation of the mechanical performance of the mortars was completed with a wear test. A Bohme machine (Ibertest, Madrid, Spain) was used to perform the abrasion test of the mortars in accordance with UNE-EN 13892-3. The tests were carried out at room temperature. Brown fused alumina (Al2O3), with an applied load of 294 N, was used as abrasive material. Three specimens of each mortar were evaluated.