Stress Self-sensitivity of Carbon Black-filled Mortar under Nondestructive Compression and the Effects of Electric Circuit and Specimen Dimensions

Cement-based materials with self-sensing capabilities have the potential to be used as compression load cells in various applications. This study aims (i) to clarify the change in resistivity in self-sensing mortar (SSM) under nondestructive compressive stress and the underlying mechanism of this change, (ii) to examine the effects of different conditions such as electric circuit and specimen dimension on this relationship. The study involved SSM specimens containing 7% carbon black powder with various parameters, including excitation voltage, intermediate resistor for the electric circuit, and electrode distance, dimensions of the cube SSM specimen. Additionally, scanning electron microscopy (SEM) observations were performed to investigate the dispersion of carbon black in the cementitious matrix. SEM observations reveal the agglomeration and dispersion of carbon black within the cementitious matrix, creating a conductive network in SSM. The measurement results showed the resistivity change was nonlinear but displayed nearly linear behavior within a specific range of compressive stress. The slope of this change increased with larger specimen cross-section, shorter electrode distance, and a smaller value for the intermediate resistor in the electric circuit. A regression analysis was conducted to predict the change in resistivity of SSM under nondestructive compressive stress, while taking these effects into account.