Carbon Nano Filaments in Cementitious Materials: Some Issues on Dispersion and Interfacial Bond

摘要

Due to their excellent mechanical characteristics, carbon nanofibers (CNFs) and nanotubes (CNTs) are expected to enhance properties such as strength, ductility, and toughness in cementitious composites. However, such enhancements cannot be achieved unless the fibers are uniformly distributed in the composite and properly bonded to the matrix. CNT/Fs tend to agglomerate due to their high level of van derWaals interactions, and typically form a weak bond with hardened cement paste matrix. This work first presents a summary of the efforts made in the past to overcome these two problems. Some typical methods of qualifying/quantifying the dispersion of CNT/Fs either in the hardened cement paste or the mix water are discussed. To demonstrate the challenges associated with CNFs and their dispersion and interfacial bond with cementitious matrices, some of the results from an ongoing experimental program are presented. The experiments investigate the effect of surfactants on dispersion and their benefits and shortcomings when cementitious composites are concerned. It was shown that mixing cement and a well dispersed water-surfactant-CNF solution may not result in a uniform distribution of CNFs in the paste or an optimal CNT-matrix interfacial bond. However, it was also found that the interfacial bond can reach to a level high enough to prevent fiber pullout.