The influence mechanism of pore structure and fiber distribution on the piezoresistive response of carbon fiber-reinforced cementitious composites

While the repeatability of the piezoresistive response in carbon fiber reinforced cement composites is known to depend on microstructure stability, the specific roles of pore structure and fiber distribution remain unclear. In this paper, the influence of porosity-fiber dual characteristics on piezoresistive stability was investigated by changing the water-binder ratio to prepare different microstructure samples under fixed carbon fiber content of 1.0%, combined with cyclic compression piezoresistive test and microscopic characterization. The results indicate that stability first increases and then decreases as the water-binder ratio increases, with the minimum coefficient of variation (cv) of 4.6% observed at a ratio of 0.22.This trend is due to three aspects: firstly, the increase of water-binder ratio reduces the gel pores and increases the macropores, which decreases the matrix compactness and weakens the mechanical support for the conductive pathway; Secondly, too low water-binder ratio results in fiber agglomeration, while too high water-binder ratio leads to fiber migration and aggregation, which reduces the effective overlapping of fibers and damages the repeatability of fractional change in resistance(FCR);Thirdly, nuclear magnetic resonance (NMR) shows that the increase of water-binder ratio increases the proportion of capillary water, which reflects the enhancement of macropore connectivity and is not conducive to the formation of stable conductive pathways. According to the comprehensive analysis, the density uniformity of pore structure and fiber distribution jointly affect the stable evolution of conductive network under cyclic loading, thus determining the repeatability of piezoresistive response, which provides a reference for understanding the root cause of its microstructure.