Microstructure and macroscopic properties of hybrid carbon nanofiber/silica fume cement composites

The effect of up to 2 wt% of “as received” carbon nanofiber (CNF) loading on the microstructural, physical, and mechanical (compressive and splitting tensile strengths) properties of hybrid CNF/silica fume cement composites has been studied. Silica fume (SF) facilitated CNF dispersion due to its small particle size and improved the interfacial interaction between the CNFs and the cement phases. The CNFs were found embedded as individual fibers throughout the paste and self-aggregated as clumps in pockets. Mechanically, the CNFs embedded in the paste and at the pocket edges acted to offset the effect of defects created by the pockets. The addition of CNFs promoted pore refinement of the composites and increased the pore volume in the 6–200 nm pore diameter range, ascribed in part to interstitial pores between the entangled CNFs.