Bifunctional Multiwall Carbon Nanotubes and Their Effect on Hydration, Conductivity, and Mechanical Properties of Cement Composites

Abstract Multiwall carbon nanotubes (MWCNTs) significantly enhance hydration reactions and properties of cement composites, expanding their applicability. Interest has grown in the use of multifunctional composites with MWCNTs being a popular filler material to impart additional features. Dispersing MWCNTs in the cement matrix creates an electrical network and replaces pore areas to enhance cement performance. This work compares two novel methods by admicellar polymerization (AP) and grafting polymerization (GP) for preparing bifunctional MWCNTs. Both techniques utilized polyindole (PIn) to enhance electrical conductivity and polyvinyl acetate (PVAc) for better dispersion. Isothermal calorimetry was used to observe the hydration of the cement composites. Results showed that AP-MWCNT/cement and GP-MWCNT/cement increased exothermic heat by 8.4% and 12.1%, respectively, compared to bare MWCNT/cement with the same nanotube content (0.3 wt%). Moreover, both modified MWCNTs improved mechanical properties and electrical conductivity. When comparing AP-MWCNTs and GP-MWCNTs in cement, AP-MWCNT/cement exhibited higher electrical conductivity, while GP-MWCNTs demonstrated superior embedding within the cement matrix, which led to a reduction in pore area and the higher mechanical strength of the two modified MWCNTs.