Effects of dispersants and defoamers on the enhanced electrical performance by carbon nanotube networks embedded in cement-matrix composites

Cementitious composites incorporating multi-walled carbon nanotubes (MWCNTs) were fabricated in this study. The effects of additive dispersants and defoamer concentrations on the electrical characteristics of the composites were experimentally investigated. Both electrically conductive (i.e., PEDOT:PSS) and insulating (i.e., SDBS) dispersants were used to enhance the colloidal dispersibility of the MWCNTs. Observations indicate that MWCNT networks embedded in cementitious composites with junctions supported by a conductive dispersant demonstrated a seven-fold enhancement in electrical conductivity. Additionally, the use of defoamers resulted in the suppressed formation of voids during the hydration process. Conductivity measurements showed that voids are disadvantageous as they result in the isolation of MWCNT networks, which are responsible for inferior electrical conductivity. Furthermore, observations revealed that the percolation threshold could be shifted by controlling the formation of voids; thus, percolation can be achieved at lower MWCNT concentrations (i.e., 0.125–0.25 wt%) than in those samples produced without defoaming additives (i.e., 0.25–0.35 wt%).