Surface-fractal-dimension characteristics of cementitious composites with multi-walled carbon nanotubes dispersed by silica fume

The effects of adding silica fume and multi-walled carbon nanotubes (MWCNTs) to cement mortar on its pore surface fractal dimension (SFD) are analyzed. The SFD is expressed through the Zhang and Li model based on mercury intrusion porosimetry (MIP) experiments. The silica fume serves as a filler and pore refiner for the paste and increases the SFD of the mesopores by forming a C–S–H gel through the pozzolanic reaction. Additionally, the well-dispersed MWCNTs increase the SFD by complicating the surfaces of the mesopores. The silica fume and MWCNTs considerably change the pore structure of the mesopores, but do not significantly affect the capillary pores. Although the correlation between the SFD and compressive strength of the cement mortar is rather poor, it has been shown to have an exponentially proportional relationship overall. Further, the SFD of the capillary pores has a greater effect than that of the mesopores on the compressive strength because of the load concentration effect.