## 2 Materials and Methods
### Mixing Process and Fresh State  
In a previous stage, the optimal water/binder and aggregate/binder ratios were obtained by changing the amount of water until a good workability was obtained for the application as a strengthening overlay. Subsequently, mixtures were formulated with consistent water to binder and aggregate to binder ratios, 0.45 and 1.5, respectively, as outlined in Table 3, illustrating the composition for 1 m\({}^{3}\) of mortar. Variation in the fibre content was the primary focus for designing these mixtures. While preserving the established ratios, this approach ensured continuity in the fundamental proportions critical for this study.  
The mixing process followed the procedure presented in Figure 3. First, the dry components were added, namely the binders, NHL 5.0 and CEM Br., and the aggregates. After mixing for 30 s, water was added and the mortar was mixed again for 120 s. After mixing the mortar, the PAN fibres were added to obtain the FRM by mixing for 180 s more, until a homogeneous mixture was obtained. Thirty seconds later, the fresh state characterization tests were carried out.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Physical Properties**} \\ \hline Fineness (\(>\)90 μm) & (\%) & \(\leq\)15.0 \\ Fineness (\(>\)200 μm) & (\%) & \(\leq\)2.0 \\ Setting time, start & (hour) & \(>\)1 \\ Setting time, final & (hour) & \(\leq\)15 \\ \hline Chemical Properties & & \\ \hline \multicolumn{1}{c}{(Sulphate) SO\({}_{3}\)} & (\%) & \(\leq\)2 \\ \multicolumn{1}{c}{(Free Lime) Ca(OH)\({}_{2}\)} & (\%) & \(\geq\)15 \\ \multicolumn{1}{c}{(Anhydrite) CaSO\({}_{4}\)} & (\%) & \(<\)1 \\ \hline \multicolumn{1}{c}{Mechanical Properties} & & \\ \hline Compressive strength at 7 days & (MPa) & \(\geq\)2 \\ Compressive strength at 28 days & (MPa) & \(\geq\)5.0 and \(\leq\)15.0 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Properties from the commercially available NHL 5.0, according to the manufacturer.  
\begin{table}
\begin{tabular}{c c} \hline \hline Density & (g/cm\({}^{3}\)) & 1.17 \\ Length & (mm) & 6 \\ Fineness & (dex) & 2.5 \\ Tensile strength & (MPa) & 580 \\ Elongation & (\%) & 14–18 \\ Elastic Modulus & (GPa) & 10.4 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Properties of PAN fibres, according to the manufacturer.  
Figure 2: Grading curve for the limestone sand and CEN Reference sand.  
The flow table test was carried out according to EN 1015-3 [45] and the resulting value was obtained by averaging the diameter measured in two perpendicular directions of the spread sample of fresh mortar, which had been placed on a table disc with the help of a cone with dimensions specified in EN 1015-3 [45]; see Figure 4a. Then, 15 vertical impacts were applied by raising the flow table and allowing it to fall freely through a height of 10 mm.  
The air content of the fresh mixtures was obtained following EN 1015-7 [46]. Accordingly, a sample of each fresh mixture was placed inside the measuring container; see Figure 4b. After closing the apparatus, water was introduced on the top of the mortar surface, and immediately after, air pressure was applied by forcing the water into the mortar and displacing all the air from within pores. The change in the water level was measured as an indication of the volume of air displaced into the fresh mixture.