# Pore Structure and Water Transfer in _Pietra d'Aspra_ Limestone: A Neutronographic Study
## 3 Results and Discussion  
### Petrographic and Physicochemical Analysis  
_Pietra d'Aspra_ can be classified as a grainstone [51] or biosparite [52]. The grain size distribution is quite heterogeneous (Figure 3a) and it is composed of at least two secondary modes, one of them being coarse-grained sand. The principal components are calcareous bioclasts, including fragments of molluscan shells, bryozoans, echinoderms, corals, and foraminifera sized up to 1-1.5 mm (Figure 3b). The most abundant accessory components are lithic fragments (0.1 mm in size), possibly derived from Mesozoic limestones and dolostones, and monocrystalline quartz grains ranging from 0.04 to 0.2 mm in size. More sporadically, clasts of siliceous rocks (quartzarenites and radiolarites) may occur. The micrite syngenetic matrix is, in general, poorly abundant, while different types of diagenetic carbonate cements have been reported, such as \"_meniscus_\" and \"_dog teeth_\". Predominantly intergranular macroporosity with cavities having a variable and irregular shape, ranging in size from 0.2 to 5 mm, has also been highlighted. Table 2 summarizes most protographic and mineralogical characteristics of this stone together with the main physical parameters [53]. As well known, mercury intrusion porosimetry does not allow determining the total volume of the stone; nevertheless, porosimetric curves give useful information about pore size distribution in the range of 200 um-0.1 um. The evaluation of the pore range, influencing the water uptake of the calcarenite, is an important factor to understand water transport properties. Grain size, grain packing, and grain contact usually control pore shape and pore size and, therefore, determine the physical properties related to water transport and storage. Pore shape seems to be of primary importance in the relationship between dynamic and static moduli of elasticity and strength. Figure 3: (**a**) Fresh cut surface of a representative specimen of _Pietra d’Aspra_ (not consolidated and not weathered, sample PA-TQ); (**b**) thin-section microphotograph of the same sample (scale bar = 0.5 mm). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Classification** & **Mean Grain** & **Colour** & **C**alcte & **Quartz** & **Dolomite** & **HCl-Insoluble** & **residue (W\%)** & **\(\rho_{\mathrm{s}}\)** \\
**(Dunham/Folk)** & **Size (mm)** & **O**\% & **O**\% & **O**\% & **O**\% & **O**\% & **O**\% & **O**\% \\ \hline BS\({}^{*}\)G & 2.4 & 107\(\times\)7/6 & 97\% & 2\% & 1\% & 5 & 2.69 \\ \hline \({}^{*}\)SiO\({}_{2}\) & \({}^{*}\)TiO\({}_{2}\) & \({}^{*}\)Al\({}_{2}\)O\({}_{3}\) & \({}^{*}\)Fe\({}_{2}\)O\({}_{3}\) & \({}^{*}\)MnO & \({}^{*}\)MgO & \({}^{*}\)CoO & \({}^{*}\)CoO & \\
2.16\% & 0.03\% & 0.55\% & 0.52\% & 0.09\% & 0.78\% & 52.54\% & \\ \hline \({}^{*}\)Na\({}_{2}\)O & \({}^{*}\)K\({}_{2}\)O & \({}^{*}\)P\({}_{2}\)O\({}_{3}\) & \({}^{*}\)Sr & \({}^{*}\)Zr & \({}^{*}\)Ba & \({}^{*}\)LOI & \\ \(<\) 0.01\% & 0.05\% & 0.05\% & 312 ppm & 2 ppm & 15 ppm & 43.23\% & \\ \hline \hline \end{tabular} Legend: BS = biosparite; G = grainstone; \(\rho_{\mathrm{s}}\) = density of the stone (g/cm\({}^{3}\)). \({}^{*}\) Data sourced from [53].  
\end{table} 
Table 2: List of petrographic, mineralogical, and physical characteristics of _Pietra d’Aspra_ samples. It appears that textural properties may represent the key parameters controlling physicochemical properties and weathering behavior. The porosimetric curve obtained for the PA-TQ sample (not consolidated and not weathered) reveals that the investigated calcarenite has an important porosity and a very wide range of pore sizes (Figure 4), highlighting the heterogeneity of pore network systems in these types of rocks. This characteristic depends on the differences in grain size and cementation degree. The pore network system is addressed in the migration of water solutions, even if the role of each dimensional range in the capillary transfer is dependent on the pore's size, shape, and connectivity.