Study on the mechanical properties, electrical conductivity, and piezoresistive behavior of multi-phase conductive fiber reinforced concrete

Single conductive materials often struggle to simultaneously achieve synergistic enhancement of both mechanical and electrical properties. In this study, a multi-phase conductive fiber reinforced concrete incorporating steel fibers and carbon fibers was investigated. A three-factor four-level orthogonal experimental design was adopted, combined with range analysis, analysis of variance, and matrix analysis to determine the optimal combination of factor levels. Based on this, the piezoresistive behavior of concrete under monotonic and cyclic loading was further investigated. The results indicate that the steel fiber content has the most significant influence on the mechanical properties, while carbon fibers mainly enhance the electrical conductivity. Considering both mechanical and electrical performance, the optimal combination is 0.95% copper-coated steel fibers and 0.48% carbon fibers. Among all the fitted curves between load and fractional change in resistivity (FCR), the copper-coated steel fiber-carbon fiber reinforced concrete (T9-T12) exhibits superior piezoresistive performance, with T-10 achieving the maximum FCR response (-78.024%). Meanwhile, T-11 demonstrates excellent cyclic stability, with a mean residual FCR of -2.32% and a standard deviation of 3.35% after six loading cycles. In addition, microstructural analyses were conducted to investigate the physical properties and conductive mechanisms of the hybrid fiber concrete. The findings of this study provide a reference for the optimized design of self-sensing conductive concrete and intelligent structural health monitoring systems.