## 3 Results and Discussion
### Physical Properties  
The determined physical properties of the mortars are listed in Table 4. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{**Mortar Identification**} & \multicolumn{1}{c}{**w/b Ratio**} & \multicolumn{1}{c}{**Flow Diameter**} & \multicolumn{1}{c}{**Bulk Density**} \\  & & **(by Weight)** & **(mm)** & **(kg/m\({}^{3}\))** \\ \hline slaked air lime & A & 1.87 & 154 (2) & 1933 (1) \\ \hline  & A+Q10\% & 1.71 & 150 (3) & 1945 (1) \\  & A+Q30\% & 1.71 & 145 * (4) & 1916 (3) \\ slaked air lime & A+Q30\%:M\({}_{1}\) (30\%) & 1.55 & 151 * (2) & 1979 (5) \\  + quicklime & A+Q30\%:M\({}_{2}\) (10\%) & 1.81 & 149 * (3) & 1906 (6) \\  & A+Q30\%:M\({}_{3}\) (5\%) & 1.81 & 149 * (2) & 1901 (2) \\ \hline slaked air lime & A+NS3\% & 1.81 & 142 (2) & 1839 (2) \\  + nano-SiO\({}_{2}\) & A+NS5\% & 1.74 & 143 (2) & 1815 (4) \\ \hline  & C:A & 1.84 & 155 (3) & 1971 (4) \\ slaked air lime & C:A:M\({}_{1}\) (30\%) & 1.50 & 151 (1) & 2052 (3) \\ + white cement & C:A:M\({}_{2}\) (10\%) & 1.82 & 151 (2) & 1970 (4) \\  & C:A:M\({}_{3}\) (5\%) & 1.79 & 150 (2) & 1959 (3) \\ \hline natural & NHL & 1.10 & 153 (3) & 1948 (3) \\ hydraulic lime & & & & \\ \hline \hline \end{tabular}  
* Flow diameter after 10 min rest; (i) standard deviation reported in brackets.  
\end{table} 
Table 3: Fresh mortars properties. As expected, the density and the porosity of the mortars varies with their compositions (Figure 4): the mortars with the addition of NS (A+NS) showed the lowest values of density and the highest porosity, while the natural hydraulic lime (NHL) mortar showed the opposite behaviour. However, despite the lower value of open porosity, the NHL mortar is characterised by a regular microstructure with heterogeneous unconnected sub-rounded macroopes (Figure 4d). In general, in all mortar compositions, there was an increase in density with the curing age without significant changes in porosity, due to the carbonation reaction. However, in NS and A+Q30%:M\({}_{1}\) (30%) mortars, a small decrease was detected from 28 to 90 days, followed by an increase from 90 to 180 days. Considering the use of different compositions, the addition of quicklime (A+Q30%) increases the bulk density (comparing with lower percentage), making the mortar more compact with low porosity (Figure 4b). In contrast, in the A+NS mortars, the density varies inversely with the concentration of the nanoparticles while the porosity, in general, presents similar values for both concentrations. This effect may be attributed to the introduction of air in the mix--due to the very small particles of nanosilica, as the closed big air bubbles do not contribute to open porosity--while reducing the density (Figure 4c). The addition of white cement to the calcium lime mortar (C:A) leads to an increase in the dry bulk density without significant changes in the open porosity values between A and C:A mortars. Considering the substitution of part of the siliceous sand by limestone aggregate, in general, the bulk density of C:A mortars increases and porosity decreases, namely in mortar with 30% of sand substitution (M\({}_{1}\)), as expected, due to the packing of finer particles in the limestone aggregate. Similar to the C:A mortars, the open porosity is also reduced for the mortars with quicklime with 30% of sand substitution (M\({}_{1}\)) (A+Q30%:M\({}_{1}\)). However, in the lime mortar with quicklime with 10% and 5% of sand substitution (A+Q30%:M2 and A+Q30%:M3, respectively), there is a decrease in density and a slight increase in porosity; this behaviour could be ascribed to the different w/b ratio, which increases with these substitutions (Table 3) and consequently increases the porosity in the hardened state.