The role of the petrophysical characteristics on the durability and conservation of some porous calcarenites from Southern Italy

Highly porous and soft calcarenites, often called "calcareous tuffs", are commonly found throughout Southern Italy and are traditionally used as building materials. The petrophysical features of some of them were determined, focusing on the microstructure (fabric and porosimetric characteristics) and on the properties related to the water absorption, drying and water vapour permeability; the compressive strength was also measured. The mineralogical composition was analysed and a variable presence of the clay minerals was found for the different varieties. Diverse levels of damage under a salt crystallisation test were related to the mineralogical, petrographic, and porosimetric features as a source of the heterogeneity of the investigated stones. Results of laboratory tests and observations of the decay in the field suggest protection against water penetration as the primary need to slow down the decay of such high porous and soft stones. Some water-repellent products were tested for effectiveness in reducing water absorption and for compatibility with the original stone properties. The use-conditions in the presence of salts were taken into account, including the performances of the treated stones under salt crystallisation test. Treatment issues were found to be strongly influenced by the porosimetric characteristics of the studied materials.