Influence of Cementitious Material Infiltration on Piezoresistive Effect of Carbon Fiber Bundle

The piezoresistive effect of carbon fibers has been successfully applied to monitor or assess the stress–strain state of carbon fiber–reinforced polymers (CFRPs). There are insufficient studies on the piezoresistive effect of carbon fabric–reinforced cementitious matrices (CFRCMs). However, the influence of mortar infiltration cannot be ignored. In this study, the piezoresistive effects of dry carbon fiber bundles, CFRP bundles, and CFRCM bundles were compared. The condition of contacting filaments was observed by electron microscopy. Before loading, the epoxy resin had little effect on the contact, and the mortar separated many contacting filaments. Therefore, the CFRP bundles and dry carbon fiber bundles have similar initial resistances, while the CFRCM bundles have a larger initial resistance. During tension, the contact ratio of CFRCM bundles decreases due to mortar infiltration, and it improves the sensitivity to tensile fracture. However, this infiltration is nonuniform, which can only affect the piezoresistive effect of the sleeve layer. Almost every core filament can contact the surrounding filaments, and the contribution of core filaments to the piezoresistive effect is negligible. The result shows that the relative resistance change of the CFRCM in the failure stage is smaller than that of the CFRP, and the curves are more discrete.