Abstract
The functionalization process usually increases the localized defects of carbon nanotubes (CNT). Thus, the ultrasonication parameters used for dispersing non-functionalized CNT should be carefully evaluated to verify if they are adequate in dispersing functionalized CNT. Although ultrasonication is widely used for non-functionalized CNT, the effect of this dispersing process of functionalized CNT has not been thoroughly investigated. Thus, this work investigated the effect of ultrasonication on functionalized CNT + superplasticizer (SP) aqueous dispersions by ultraviolet-visible (UV-Vis) spectroscopy, dynamic light scattering (DLS), and Fourier transform infrared spectroscopy (FTIR). Furthermore, Portland cement pastes with additions of 0.05% and 0.1% CNT by cement weight and ultrasonication amplitudes of 0%, 50% and 80% were evaluated through rheometry, isothermal calorimetry, compressive strength at 1, 7 and 28 days, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). FTIR results from CNT + SP dispersions indicated that ultrasonication may negatively affect SP molecules and CNT graphene structure. The increase in CNT content and amplitude of ultrasonication gradually increased the static and dynamic yield stress of paste but did not significantly affect its hydration kinetics. Compressive strength results indicated that the optimum CNT content was 0.05% by cement weight, which increased the strength of composite by up to 15.8% compared with the plain paste. CNT ultrasonication neither increases the degree of hydration of cement nor the mechanical performance of composite when compared with mixes containing unsonicated CNT. Overall, ultrasonication of functionalized CNT is not efficient in improving the fresh and hardened performance of cementitious composites.
Highlights
The effect of ultrasonication of superplasticizer (SP) molecules has not yet been reported. Considering this gap in knowledge, the aim of this work is to elucidate the influence of the ultrasonication process on rheology, hydration kinetics, compressive strength, and microstructure of cementitious composites with functionalized carbon nanotubes (CNT) without ultrasonication and pastes with CNT that were previously ultrasonicated with two amplitudes
UV-Vis spectroscopy was used to evaluate the quality of CNT dispersions in water
dynamic light scattering (DLS) and Fourier transform infrared spectroscopy (FTIR) tests were performed to complement the characterization of the CNT dispersions
Summary
The use of carbon nanotubes (CNT) is still limited due to difficulties associated with the dispersion of these nanomaterials and their weak interaction with cementitious matrix. This is because CNT, unlike other spherical particles and carbon fibers, are characterized by small nanometric diameters, high aspect ratio (>1000), and, a large surface area [1,2]. The effect of CNT on the mechanical performance of cement-based materials is not a consensus in the literature. Some authors have reported that CNT significantly increased the mechanical performance of cementitious composites.
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