K/Na-silicate, ethyl-silicate and silane nano-molecular treatments in the restoration of high porous limestone

Carbonate sedimentary rocks (i.e., limestones) have been frequently used in historical times due to easy availability and workability. These latter depend primarily by petrophysical characteristics (porosity, bulk density) that influence the mechanical strength. However, the limestones with high porosity (>30%) and a poorly cemented carbonate-matrix show chemical alteration (i.e., dissolution) and physical decay (e.g., decohesion). In this work it was taken as case study a biomicritic limestone belonging to the carbonatic miocenic series (lower Tortonian) of Cagliari (southern-Sardinia, Italy). This limestone has a low-medium cementing matrix containing hygroscopic clay and sea-salt phases, which make the rock degradable. To limit the decay it can intervene with consolidating products (K-Na-silicate, ethyl-silicate) and protective-chemicals (silane nano-molecular gel-coat) to reduce the porosity and permeability to the liquid aqueous phase. Results highlight an increase of strength after consolidation and a decrease of gas-permeability after protection-treatment, maintaining in both cases a good permeability to the vapor-phase.