Tomographic Imaging of Cementitious Materials

Cement-based materials such as concrete are brittle in nature and crack when subjected to tensile strain. Current strategies for crack detection are primarily based upon visual inspection by trained inspectors, but such approaches are labor-intensive and expensive. Direly needed are sensors that can be incorporated into structural health monitoring systems for automated quantification of crack damage. As cementitious composites remain the most dominant construction materials of structures, this study explores the use of these materials as their own sensor platform capable of measuring mechanical behavior under loading. Fundamentally, this self-sensing functionality is achieved based upon electromechanical properties. First, the piezoresistivity of cementitious composites is quantified to establish the material as a multifunctional system that is 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. The featured 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 that 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 three-point bending.