A discussion on the determination of permeability and absorption in concrete

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. The quality and functional performance, the state of conservation, and possible pathologies of stone materials of structures and building envelopes, as a norm, have to be evaluated by performing tests and samplings with a minimal degree of invasiveness. This last requirement, aiming at the limit of nondestructive testing, stems from the necessity to find a balance among preservation of structural, historical, and artistic integrity of the inspected stone materials, an acceptable level of gained knowledge on the built element, and sufficient reliability of the deployed diagnostic activities. While the requirement of least invasiveness is common to many inspective and diagnostic practices belonging to different technical sciences, such as structural engineering, architecture, and restoration, as well known, however, the conditions of minimum knowledge gain and minimum acceptable reliability can be seldom granted by methods of testing that are completely nondestructive. The last century of investigations has shown the pivotal role of permeability for durability assessment of building stones and concrete, with the possibility of reducing invasiveness by using smaller stone samples in uniaxial water-permeation tests. This contribution presents a review on past and present experimental methods for determining permeability in concrete, some of which are also applicable to other porous building materials, with a discussion on optimality criteria for testing and sampling which is carried out in the light of an historical perspective and of a view towards the Life Cycle Assessment of interventions on the built heritage.