Influence of MWCNT/surfactant dispersions on the rheology of Portland cement pastes

This work studies the effect of MWCNT/surfactant aqueous dispersions on the rheology of cement paste. Three types of surfactants (sodium dodecyl sulfate, cetylpyridinium chloride and triton TX-100) were used to prepare cement pastes with and without MWCNT. Three rheological parameters were determined for each sample: static yield stress, yield stress, and viscosity. The first was measured directly, while the other two were obtained by fitting a Bingham model to the descending portion of a flow curve. Additionally, X-ray diffraction and isothermal calorimetry were used to follow the hydration reaction of cement during the first hour. It was found that the MWCNT/surfactant dispersions generate an overall shift to higher yield stress values while maintaining viscosity, suggesting a modification of the interparticle attraction. It was concluded that the triple interaction MWCNT-surfactant-cement governs the rheology of cement pastes. © 2018 Elsevier Lt

Reinforcing Effect of Carbon Nanotubes/Surfactant Dispersions in Portland Cement Pastes

Decoupling the individual effects of multiwalled carbon nanotubes (MWCNTs) and surfactants when used as reinforcement materials in cement-based composites is aimed in this study. Powder MWCNTs were dispersed in deionized water using different types of surfactants as chemical dispersing agents and an ultrasonic tip processor. Cement pastes with carbon nanotubes additions of 0.15% by mass of cement were produced in two steps: first, the MWCNT/surfactant dispersions were combined with the mixing water, and then, cement was added and mixed until a homogeneous paste was obtained. Mechanical properties of the pastes cured at 7 days were measured, and their fracture behavior was characterized using the linear elastic finite element analysis. It was found that the reinforcing effect of MWCNT was masked by the negative effect of surfactants in the cement matrix; nevertheless, nanotubes were capable of increasing both stress and strain capacity of the composite by controlling the crack propagation process at the tip of the crack. © 2018 Oscar A. Mendoza Reales et al

Testing industrial laboratory dispersion method of Multi-Walled Carbon Nanotubes (MWCNTs) in aqueous medium

The carbon nanotubes (CNTs) dispersion has gained interest in recent years due to its multiple applications in fields such as electronics, concrete, optics, environmental, automotive, marine and aeronautics coatings. In this sense it is necessary to develop stable dispersions of CNTs. On a laboratory scale the method of preparation of the CNTs is usually done using sonication, but this method is not appropriate to obtain CNTs dispersions on a larger scale. This work studies Multiwalled Carbon Nanotubes (MWCNTs) in aqueous medium comparing an industrial laboratory dispersion method vs traditional sonication. A factorial experimental design was performed, considering as variables: dispersion method, type of surfactant and use of a rheological modifier. The samples were prepared according to the full factorial DoE and properties such as electrical conductivity and pH were studied. Stability measurements were carried out over time and charge stability studies were performed using zeta potential measurements. The results shown the best combination of variables for the electrical conductivity was: dispersion method, sonication; dispersant, TX-100; rheological modifier, present. Although the results show that an improvement in CNTs dispersion is not achieved with the grinding and the use of industrial additives, the additive Disperbyk 2012 presented the highest value of electrical conductivity as a lonely compound, but the final electrical conductivity obtained when using it was not so high, it indicates that this additive must have specific conditions of activation, which implies that a further experimental work is required in order to get a suitable working window that allows a combination of variables with greater industrial application. © Published under licence by IOP Publishing Ltd