Electromechanical behavior in damage detection of self-sensing cementitious composites containing carbon nanotubes and polypropylene fibers

Abstract This study investigates the self-sensing capabilities of cement pastes containing multi-walled carbon nanotubes (CNT) and polypropylene (PP) fibers. The primary objective is to evaluate the variations in the electrical properties of the composite as a function of damage initiation. Tensile splitting tests were employed as a controlled damage induction method, ensuring the formation of a single, well-defined, and localized crack. This experimental approach allows for a precise correlation between structural damage and corresponding alterations in electrical resistivity. Specimens were prepared with five different CNT concentrations, ranging from 0.00% to 1.00%, and a fixed 0.50% content of PP fibers by volume of cement paste. Electrical resistivity measurements identified the percolation threshold at 0.12% CNT, with the material entering the stable conduction zone between 0.50% and 0.75% CNT. The 0.50% CNT concentration, which is situated within the transition zone, yielded the highest sensitivity to cracking, with the fractional change in resistivity (FCR) reaching values between 125% and 500% at the moment of failure. While higher CNT concentrations (0.75% and 1.00%) provided superior electrical conductivity, they exhibited less sensitivity due to their denser conductive networks. In contrast, lower concentrations proved ineffective for damage detection. This research demonstrates that the exceptional electrical properties of CNT, combined with the crack-bridging effect of PP fibers, create a multifunctional synergistic composite. This combination yields both high electromechanical sensitivity and crack control, demonstrating the viability of this smart material as an intrinsic sensor for Structural Health Monitoring in civil infrastructure.