Influence of electrophoretic deposition of micro- or nanosized silica particles on the microstructure of carbon fibers and their bond behavior with cementitious matrices

The application of carbon fiber (CF) reinforced cementitious composites is often restricted by the poor load transfer between the components. In this study, two reactive coating materials—nano-silica and micro-silica—are utilized to modify the CF surfaces via an electrophoretic deposition approach. These negatively charged particles are able to be electrosorbed onto the fiber surfaces under a constant electrical field according to the zeta and cyclic voltammetry measurements. After surface treatment, XRD analysis of CFs showed an increase in graphite crystallite thickness and decrement in interlayer spacing <d₀₀₂, significantly affecting the fiber diameters. Additionally, the lengths of crystallites were reduced, which can impair the fiber strength and their temperature stability. Single fiber pullout tests exhibited that the interfacial bonding can be clearly enhanced by both reactive coatings. Microscopic observation revealed that C–S–H gel and calcite structures can be formed near the fiber surfaces after immersion in cement pore solution owing to pozzolanic reaction and nucleation effect, tremendously heightening both chemical and mechanical interaction between fiber and cement. Finally, based on a detailed micromechanical analysis, the reinforcing mechanisms between the differently modified fibers and the cementitious matrix were elaborated and discussed.