Carbon black dispersions in conductive cementitious composites: Mechanistic insights into the interrelationship between dispersion behaviour, electrical properties and microstructures

Despite carbon black being explored as a promising additive in cementitious materials, its use remains challenging due to issues associated with its effective dispersion in concrete, which typically result in non-uniform distribution and agglomeration of CB, negatively impacting the mechanical performance and electrical conductivity of electrically conductive cementitious composites (ECCC). This work comprehensively investigates the effects of polycarboxylate ether (PCE) superplasticizer (SP), ultrasonication (US), water-to-cement (w/c) ratio, and treatment sequence of SP addition and US application on CB dispersion in ECCC. Quantitative and semi-quantitative assessment of CB dispersions in aqueous media and simulated pore solution are performed through dynamic light scattering and visual imaging methods, respectively. CB content decreases the overall resistivity of ECCC, US treatment reduced particle size in ECCC and reduces resistivity at certain PCE SP dosages, while increasing PCE induces a similar “percolation threshold” mechanism on ECCC, and introduced non-ohmic conduction behaviour. Increased agglomeration with excess PCE dosage is also observed in the simulated pore solution, which may relate to the critical micelle concentration (CMC) of PCE. Furthermore, presence of PCE allows cations in cement to dissolve and later crystallize in CB agglomerates, which may contribute to ECCC's non-ohmic behaviour. This work provides insights into interactions between cement, PCE, and CB and its effect on ECCC properties, as well as a method to examine dispersions of conductive fillers in solution and ECCC.