Effect of pozzolanic micro and nanoparticles as secondary fillers in carbon nanotubes/cement composites

•Pozzolanic micro and nano particles (nanosilica, microsilica, metakaolin and nanoclay) were used as secondary fillers.•Microparticles are much more effective than nanoparticles in increasing the compacity and effective nanotube volume in the matrix.•Surfactants as dispersing agent for CNT have a retardation effect on the hydration and strength development of cement paste. Incorporation of micro and nanoparticles as secondary fillers in cement based matrices improves the efficiency of self-sensing carbon nanotubes (CNT)/cement composites through the excluded volume effect. Pozzolanic particles can be seen as interesting secondary fillers for this purpose since they would increase the compacity of the granular matrix, increase the nanotube effective volume during the first hours of hydration, and densify the matrix through the growth of additional hydration products at latter ages. In this work, pozzolanic micro and nano particles (nanosilica, microsilica, metakaolin and nanoclay) were used as secondary fillers to investigate how their combined effect with CNT dispersion containing surfactant as dispersing agents affects the hydration kinetics, setting time and early strength development of Portland cement pastes. For this purpose, isothermal calorimetry and ultrasonic pulse velocity tests were performed. The change in solid fraction caused by the pozzolanic particles also was analyzed to understand the excluded volume effect in the matrix. It was found that the use of surfactants as dispersing agent for CNT has a retardation effect on the hydration and strength development of cement paste and this retardation is minimized by the presence of pozzolanic secondary fillers. It also was found that microparticles are much more effective than nanoparticles in increasing the compacity and effective nanotube volume in the matrix.