One century of theoretical and applied mechanics of concrete and stone materials permeability. What have we learned?

Periodic and non-routine inspections on buildings, infrastructures, and sites of historical or architectural interest frequently involve a necessary deepening of the knowledge of natural or artificial stone materials of the built heritage. Insight into stone materials is of particular relevance when the problem is approached of fine-tuning best practices for assessment and maintenance within Life Cycle Assessment methodologies, in the light of an increased awareness that social, infrastructural and environmental issues and policies cannot be faced by single compartments but need comprehensive evaluation. Permeability has been early recognized as a basic property for the assessment of durability of concrete and stone materials. This contribution reports and discusses selected conclusions of studies which have scrutinized a large body of theoretical and technical scientific literature on permeability testing of concrete, as well as of regulatory literature, keeping a historical perspective and a focus in pinpointing fundamental open research issues of both theoretical and applied relevance in the mechanics of permeation of fluids through porous media. The fundamental experimental studies conducted in the first decades of last century are also the starting point for an assessment of the continuum mechanics and thermodynamics equations describing the flow of compressible fluids in porous media and for a critical review of the approach of current European standards to the determination of concrete watertightness.