Effect of a Carbon Nanotube/Surfactant Aqueous Dispersion on the Rheological and Mechanical Properties of Portland Cement Pastes

Abstract

Multiwalled carbon nanotubes (MWCNT) are expected to enhance the load transfer and increase the flexural strength of a MWCNT-cement composite by working as bridges for load across cracks. For this, an adequate dispersion degree of nanotubes throughout the matrix must be obtained, surfactants being one of the most used chemical-dispersing aids to attain this goal. A commercial MWCNT/surfactant aqueous dispersion was used to produce cement pastes with MWCNT additions up to .25% by mass of cement. Rheological behavior and mechanical performance were used to characterize the influence of nanotubes on the cement paste. It was found that the MWCNT/surfactant dispersion studied decreased the workability and mechanical properties of the cement paste, regardless of micrographs showing that MWCNT acted as bridges across submicrometric cracks. This was due to a delay of the hydration reaction of cement and an increase of the amount of entrapped air caused by the presence of surfactant. It was concluded that the reinforcing effect of nanotubes was masked by the negative effects of the surfactant on the mechanical performance of the matrix.