Force-electric properties of smart cementitious composites reinforced with carbon fiber and conductive recycled fine aggregates

A type of intelligent cement mortar was created in the laboratory to achieve higher piezoresistive sensitivity for self-health monitoring of concrete structures and to address the reduction in mechanical properties caused by using recycled fine aggregate (RFA). It is a type of cement-based material that natural fine aggregate is partially replaced with highly conductive modified recycled fine aggregate (M-RFA) treated with graphite powder-agar gel impregnation, and a small amount of carbon fibre (CF) was uniformly distributed in the M-RFA mortar to construct a three-dimensional conductive network. The paper studied the intelligent cement mortar's workability, mechanical properties, conductivity, and piezoresistive performance. The results show that the content of M-RFA has little effect on the working performance of the composites, and CF significantly affects the working performance of the composites, which can meet the requirements after adding a superplasticizer. The addition of M-RFA will reduce the mechanical properties of smart cement mortar, but the multi-doped carbon fibre can restore the reduction of mechanical properties caused by M-RFA. Since CF helps M-RFA to be embedded in a conductive network by directly connecting M-RFA or tunnelling effect, conductive mortars doped with CF and M-RFA can significantly reduce resistivity, improve piezoresistive sensitivity, and improve signal stability. The loading rate affects the piezoresistive properties of cement mortar, and the strain sensitivity is negatively linearly correlated with the loading rate. It is worth noting that the conductive mortar with 0.24 vol% carbon fibre and 80 % M-RFA content achieves the highest strain sensitivity (836.9), lower resistivity (150.1 Ω•cm), and the best economy. •High-conductivity RFA was prepared by impregnating RFA with graphite powder agar gel.•Conductive RFA was linked using CF, forming a 3D conductive network in composites.•Conductive mortar achieves low resistivity and high strain-sensing sensitivity.•Composites that combine CFs and modified RFA can improve mechanical properties.•The loading rate's effect on the composite's piezoresistive properties was studied.