Strategic strengthening of the interfacial transition zone (ITZ) between microfiber and cement paste matrix with carbon nanofibers (CNFs)

The interfacial transition zone (ITZ) governs the mechanical properties and durability of fiber-reinforced cement-based composites. It has been reported that strategic strengthening of the ITZ by simple coating of carbon nanofibers (CNFs) on microfibers resulted in a 22% enhancement of the fiber/matrix bond. In the current study, ingenious methods were used to characterize such CNF-reinforced ITZ (CNF-ITZ). Results show that strategic application of CNFs greatly densified the ITZ with much reduced voids and defects. A distinctive hairy microstructure, resembling the setae on the toes of geckos, and less portlandite were found in the CNF-ITZ. The indentation hardness and indentation modulus were enhanced in both the radial and the tangential directions. The resulting CNF-reinforced ITZ is tougher and stronger with improved mechanical properties against deformation and cracking, which leads to enhanced fiber/matrix bond and elevated load transfer efficiency between fiber and matrix.