Electromechanical properties of multi-reinforced self-sensing cement-based mortar with MWCNTs, CFs, and PPs

This experimental research examines the electromechanical properties of hybrid cement-mortar composites strengthened with different amounts of multi-walled carbon nanotubes (MWCNTs), carbon fibers (CFs), and polypropylene microfibers (PPs). The experimental program included optimal mechanical improvement at the nano and micro levels. The optimum micro-composite mortar derives from the finest mechanical response of the CFs and PPs micro-modified specimens in terms of flexural and compressive strength. Further, the electrical response of the mortars with the improved mechanical response was examined. The improved mechanical and electromechanical response of the optimum amounts of the two scales indicates the hybrid mortar with exceptional performance. This optimum amount in micro-scale in synergy with the optimum amount of MWCNTs constituted the hybrid-reinforced cement-based mortar. The optimized nano-, micro-, and hybrid-reinforced mortars were examined for their electrical properties in terms of electrical conductivity, impedance, and piezo-resistivity. These measurements in combination with the Nyquist plots of the resistance-reactance specified the sensing ability of the cementitious self-sensor. Results indicated that the optimum reinforcement in the nanoscale is 0.2 wt% MWCNT and in microscale 0.5% wt.% CFs exhibited improvement in flexural strength, compressive strength, and flexural toughness. The optimum nano- and micro-reinforced cement-based mortars presented much higher conductivity of about 867% and 633%, and lower impedance of about 89.4% and 86%, respectively, compared to the reference specimen, and a one-order-of-magnitude compared to the other contents. The excellence of the hybrid combination of 0.2 wt% MWCNΤs and 0.5% wt.% CFs occur with even more improved flexural strength of about 27%, flexural toughness of about 1607%, conductivity of 2617% more than the reference mortar, and lower impedance of about 96%, compared to the reference specimen. The piezoresistive response of the tested cement-mortar composites denotes the enhanced strain-sensing ability of the examined multi-reinforced mortars, highlighting the superiority of the hybrid one.