Damage-sensitive electrically conductive mortars: a novel laboratory characterization method and initial numerical simulations

In this paper, the authors propose innovative damage-sensitive electrically conductive mortar layers to monitor crack formation and propagation in masonry structures. The inclusion of a sufficient amount of suitable electrically conductive fillers in cement mortar formulations is shown to promote the development of an improved electromechanical response of the material, which can be exploited for Structural Health Monitoring (SHM) purposes. Specifically, consistent changes in the electrical conductance of doped mortar joints with increasing tensile damage are observed in the proposed mortars even at the micro-cracking stage, thus aiding in the identification of early-stage damage. Besides introducing the aforementioned idea, this paper presents a methodology to characterize the electromechanical response of different conductive mortar formulations under increasing cracking states. Three-point cyclic bending tests were conducted on mortar prismatic samples using a staircase-triangular shaped displacement history, while electrical measurements were performed stimulating the material with a biphasic voltage signal input. Correlations between the mortars’ electrical outputs with stress/strain time histories from material testing were evaluated to define degradation curves linking decays in material electrical conductance and progressive damage states, the latter expressed as degradation of the elastic moduli of the tested mortar specimens according to the concrete damaged plasticity constitutive model, combining isotropic damaged elasticity and isotropic tensile and compressive plasticity. The obtained results highlight the promising crack detection capabilities possessed by the investigated mortar formulation. The obtained degradation curves are also demonstrated to effectively refine the mortar’s electromechanical response for multiphysics models used in the numerical simulation of masonry structures with self-sensing damage detection capabilities.