Electrical impedance tomography to monitor unsaturated moisture flows, and to detect corrosive elements and cracking in cementitious materials

Electrical impedance tomography (EIT) is an imaging modality which uses electrical measurements to reconstruct two- or three-dimensional (2D/3D) electrical conductivity distributions in target objects. In this paper, we discuss two recent applications of EIT in structural health monitoring. First, we study the feasibility of EIT for imaging unsaturated moisture flows in cement-based materials. In the experiments, specimens are monitored with EIT during the water ingress in the specimens. The results indicate that EIT is able to detect the moisture movement and to show approximately the shape and position of the water front. Secondly, we develop EIT -based surface sensing systems, or sensing skin, for detecting and localizing the ingress of chlorides and cracking - two phenomena which are of concern in many structures, including reinforced concrete structures. In the experiments, the sensing skins are tested using concrete substrates. The results demonstrate the feasibility of a singlelayer sensing skin for detecting cracks, and further, show the potential of a multi-functional multi-layer sensing skin for simultaneously detecting corrosive elements and cracks, and for distinguishing between them.