The influence of moisture content on the piezoresistive effect of CFRCM bundles during pull-out tests and the modification of its piezoresistive model

Carbon Fabric Reinforced Cementitious Matrix (CFRCM) can serve dual functions of structural strengthening and sensing owing to the excellent electrical conductivity of carbon fibers. The moisture content of CFRCM significantly influences the electrical conductivity of carbon fibers. To investigate the effects of moisture content on the mechanical properties and piezoresistive effect of CFRCM bundles, pull-out tests were conducted on CFRCM bundles with moisture content ranging from 0 to 10%. The test results indicate that moisture content has no effect on the peak load of the specimens; however, the peak displacement corresponding to the peak load increases with higher moisture content. In the elastic loading stage, the resistance of most specimens increases with strain, accompanied by fluctuations in the measured resistance. When the moisture content is 8%, the resistance fluctuations are most pronounced. The effect of moisture content on the resistance of the carbon fiber bundle is negligible. Instead, moisture content primarily affects the initial resistance and displacement of the CFRCM bundles. Based on these findings, the piezoresistive model was modified. The corrected model accounts for an increased number of fibers in the carbon fiber bundle sleeve layer, enhancing the load-bearing capacity of the CFRCM bundle and improving the accuracy of the results. This study provides a theoretical foundation for the intelligent health monitoring of concrete structures under varying moisture conditions.