## 2 Materials and Methods  
### Materials and Mortar Compositions  
Several mortar formulations were studied in the process of selecting adequate repair mortars, in order to fulfil the requirements of compatibility with the ancient masonry and renders from the physical, mechanical, and chemical points of view [33; 34] while ensuring adequate durability.  
Since the original mortars were based from calcitic air lime with clay-free siliceous sand [6], the first mortar formulations were based from lime with natural siliceous sand (RT) from the Tagus River, supplied by Lena Agregados, SA.  
Moreover, several lime lumps, measuring a few centimetres, were also found in the renders (Figure 2), suggesting that the lime was not well mixed during the mortar kneading or was prepared by a hot-mixing procedure [35]. Using a lower burning temperature could confer highly reactive lime with good plasticity and workability [36], as well as some physico-mechanical properties to the mixture, that favour the overall compatibility of the system [37].  
The properties of the raw materials are presented in Table 1.  
Therefore, to approach the original mortar compositions, lime-based mortars with slaked air lime (A) and slaked air lime + quicklime (A+Q) were formulated in this study, using a binder/aggregate ratio (in volume) of 1:2. Further, to give some hydraulicity and additional strength to the mortars to be applied in this severe marine environment, slaked air lime mortars with the addition of nanosilica (A+NS) were considered using approximately the same binder/aggregate ratio as the reference mortars. The proportions of quicklime and nanosilica were chosen according to previous research works [19; 21; 22] and also taking into account previous exploratory practical tests in laboratory, carried out with lime pastes, conducted to choose proportions of slaked lime-quicklime and lime-nanosilica that minimize shrinkage. Beyond that, moderately hydraulic mortars mixes as White Portland cement + slaked air lime (C:A) and natural hydraulic lime (NHL) mortars, with a binder/aggregate ratio (in volume) of 1:3:12 and 1:3, respectively, were also used [13].  
Furthermore, as calcareous shells were detected in the original mortars [6], and in order to align more closely with the original formulation, as well as to improve the mortar's performance, a fine-tuning of the aggregates, substituting part of the siliceous sand by limestone aggregate in 30% (M\({}_{1}\)), 10% (M\({}_{2}\)) and 5% (M\({}_{3}\)), by volume (Table 2 and Figure 3), was made into two mortars compositions, A+Q30% and C:A.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Material Identification** & **Acronym** &
\begin{tabular}{c} **Bulk Density** \\ **(kg/m3)** \\ \end{tabular} \\ \hline \multirow{4}{*}{Binder} & Calcium hydrated lime (in powder form) CL90-S & A & 359 \\  & Calcium quicklime\_CI90-Q (R5, P2) & Q & 729 \\  & Natural hydraulic lime\_NHL 5 & NHL & 782 \\  & White Portland-limestone cement\_CEM II/B-I. 32.5R & C & 926 \\ \hline \multirow{4}{*}{Sand} & Natural siliceous sand from Tagus River 0/2 mm & RT & 1448 \\  & Calcareous sand 0/1 mm & C & 1308 \\  & Mix of 70\% RT and 30\% C sand & M\({}_{1}\) & 1517 \\  & Mix of 90\% RT and 10\% C sand & M\({}_{2}\) & 1479 \\  & Mix of 95\% RT and 5\% C sand & M\({}_{3}\) & 1470 \\ \hline nano-SiO\({}_{2}\) & Aqueous colloidal dispersion of nano-sized silica 10/20 nm & NS & 57 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Identification and properties of the raw materials.  
Figure 2: Time lumps found in the renders of Paimogo’s Fort.  
The mortar compositions are summarized in Table 2.  
Figure 3: Grain size distributions of the used sands.