Characterization of the interfacial transition zone of CNF-Reinforced cementitious composites

Carbon nanofibers (CNFs) has become one of the most promising nanomaterials as an additive to cementitious composites, due to the improvements that can be seen in mechanical, electrical and thermal properties. Mechanical characterization has been conducted with cement paste, mortar and concrete with 0.1 wt% well-dispersed CNFs, and the modulus of elasticity is found to be improved by 21%, 34% and 29%, respectively. The improvement is more significant in mortar and concrete in spite of the presence of aggregate which reduces the volume fraction of CNFs, indicating a potential enhancement in the interfacial transitional zone (ITZ). The nano-characterization of the ITZ is performed in CNF-modified mortars and concrete using atomic force microscopy (AFM) and energy-dispersive X-ray spectroscopy (EDS). The results show the ITZ is enhanced mechanically (elastic modulus is increased) and chemically (Ca/Si ratio is reduced) due to the addition of CNFs. The characterization of the ITZ in the presence of CNFs offers an explanation for the different behaviors seen in nano-modified cement paste, mortar and concrete and facilitates the use of CNF in concrete in field applications.