An Experimental Investigation of the Effects of Grain Size and Pore Network on the Durability of Vicenza Stone

The textural properties of a rock and the characteristics of its pore network are intrinsic variables to consider when investigating the resistance of rock to weathering. To establish the influence of these variables on the effectiveness and progression of weathering processes, two lithotypes of a limestone were analyzed with respect to their texture and porosity, and to their performance during artificial weathering experiments. The studied rock is Vicenza Stone, a bioclastic limestone with heterogeneous texture, variable grain size from fine to coarse, and high levels of open porosity (27-28%). Two sets of samples were obtained from a quarry, defining coarse-grained (CGV) and fine-grained (FGV) lithotypes of Vicenza Stone. Multiple techniques (optical microscopy, scanning electron microscopy, image analysis, mercury intrusion porosimetry, hygroscopicity, ultrasound, and water absorption) were used to characterize the texture and porosity of the limestone. The sample sets were subjected to freeze-thaw (UNI 11186:2008, Cultural heritage-Natural and artificial stone-Methodology for exposure to freeze-thawing cycles, 2008) and salt-crystallization (partial continuous immersion method with a Na2SO4-saturated saline solution) weathering experiments to investigate the processes and progression of mechanical and chemical weathering. Differences in freeze-thaw-induced micro-cracks and in the deposition of secondary micrite between the lithotypes show that the CGV has an overall higher susceptibility to freeze-thaw weathering than FGV. Salt-weathering processes induced micro-crack formation, material dissolution, and secondary precipitation, suggesting the simultaneous occurrence of mechanical stress and chemical dissolution-precipitation processes. FGV is more prone to salt-induced weathering than CGV, whereas CGV is susceptible to the wide thermal excursions of freeze-thaw weathering.