Enhancement of strength and ductility of cement-based composites by incorporating silica nanoparticle coated polyvinylalcohol fibers

Addition of fibers can give brittle material extrinsic toughness, mainly because of the bridging effects. However, such behavior is highly dependent on the interfacial interaction between fiber and brittle matrix. In order to optimize both the strength and ductility of cement, which is the most extensively used brittle material on this planet, here we propose a new strategy to control the interfacial property in the fiber-cement matrix. Silica-coated polyvinylalcohol fibers were successfully synthesized by a sol-gel method with controlled silica thickness, and then incorporated into cement paste. The interaction between fibers and cement matrix was significantly enhanced due to the greatly increased hydrophilicity and roughness of silica-coated fibers, as well as the pozzolanic reactivity of silica nanoparticles. Therefore, the interfacial region between fiber and cement becomes much more compact, promoting the fiber-cement interaction both physically and chemically. As such, the crack propagation would be severely constrained, resulting in the strength and ductility of cement significantly increased. We showed that the ultimate flexural strength and ultimate deflection of the cement composites reinforced by silica-coated polyvinylalcohol fibers increase by 187% and 980% with respect to pristine cement, and increase by 28% and 74% compared to cement reinforced by polyvinylalcohol fibers without silica, at the fiber content of 1 wt.%. This study illustrates the potential and effectiveness of interfacial design to overcome the mechanical dilemma of strength and ductility increase simultaneously, and open a new dimension to further improve the mechanical properties of cement.