Dispersion of multi-walled carbon nanotubes and its effects on the properties of cement composites

Abstract

In this study, two types of multi-walled carbon nanotubes (pristine, p-CNT and functionalized, f-CNT) were dispersed in water by sonication and then added to cement mortar. The purpose of this study was to characterize the dispersion degree of the CNTs in aqueous suspension and to investigate whether achieving dispersion in water would also result in dispersion inside mortar. Dispersion of the CNTs in water was investigated by means of UV-vis spectroscopy, using different CNT concentrations and sonication durations. Dispersion of the CNTs in cement mortar was investigated by measuring the compressive and flexural strength and fracture toughness as well as the microstructural characterizations of scanning electron microscopy and mercury intrusion porosimetry. The effects of the CNT addition on drying shrinkage and cement hydration were also investigated for cement pastes. The results of UV-vis spectroscopy showed that by increasing the sonication time to 120 min, the dispersion degree of the f-CNT suspension increased progressively, while for p-CNT, a maximum was reached with 60 min of sonication. The compressive and flexural strength and fracture toughness of mortars containing f- and p-CNTs were not significantly improved either by increasing the amount of CNT or imposing sonication in mixing water. High CNT dispersion in cement matrix was not equally obtained by utilizing highly dispersed CNT suspension. Sonication of f- and p-CNT led to a remarkable deceleration of cement hydration in the first hour of hydration and drying shrinkage of the cement composites was found to be reduced by f- and p-CNT addition

Nanomaterials in Structural Engineering

“…Interestingly, the addition of CNTs decreases the drying shrinkage of composites. Indeed, the authors [34] attributed this behavior to the reduction of micropores. It is worth noting that the influence of CNTs on the microstructure, porosity, and thereby mechanical properties of cementitious composites is highly dependent on the quality of their dispersion within cement matrix as well as on the type of surfactant to be used.…”

Nano-Inclusions Applied in Cement-Matrix Composites: A Review

“…Nevertheless, Fattah et al [137] described how functionalization with the –COOH group increased the solubility and the bonding strength of CNTs in the cement matrix [54]. Isfahani et al [143] did not find any improvement in the dispersion process when applying sonication to the CNT suspension in water and, then, adding it to the cement mortar. With the scope of adding CNTs to cement matrices, Stynoski et al [144] enhanced the solubility of CNTs in water through their functionalization with nanosilica particles.…”

The Effect of Carbon Nanotubes on the Flowability, Mechanical, Microstructural and Durability Properties of Cementitious Composite: An Overview

“…Some authors report a slight increase in the flowability of modified concrete where a proper CNT dispersion technique and mixing process was used [10,[16][17][18]. Some studies were carried out to investigate the effects of CNTs on the hydration of cement composites [19][20][21][22][23][24] and research results show that CNTs effectively influence the hydration of cementitious composites. CNTs most often accelerate the hydration process and add to the development of higher heat during hydration.…”