Electrical Impedance Tomographic Methods for Sensing Strain Fields and Crack Damage in Cementitious Structures

Cement-based composites (for example, concrete) are brittle materials that crack when loaded in tension. Current strategies for crack detection are primarily based upon visual inspection by an inspector; such approaches are labor-intensive and expensive. Direly needed are sensors that can be included within a structural health monitoring (SHM) system for automated quantification of crack damage. This study explores the use of cementitious materials as their own sensor platform capable of measuring mechanical behavior under loading. Fundamentally, this self-sensing functionality will be based upon electro-mechanical properties. First, the piezoresistivity of cementitious composites is quantified so as to establish the material as a multifunctional system capable of self-sensing. Second, electrical impedance tomography (EIT) is proposed for measuring internal strain fields using only electrical measurements taken along the boundary of the structural element. An inherent advantage of EIT is that it is a distributed sensing approach offering measurement of strain fields across 2D or 3D. Furthermore, the approach is well suited for imaging cracks which appear as conductivity reductions in EIT-derived conductivity maps. Finally, to validate the accuracy of the EIT technique, it is applied to fiber reinforced cementitious composite elements loaded by axial tension-compression cycles and 3-point bending.