Vanessa Vilela Rocha

The inclusion of carbon nanotubes (CNTs) in cementitious composites has been studied due to their electrical, thermal, and mechanical enhancing properties. Considering the hydrophobic characteristics of CNTs, these nanomaterials need to be well dispersed in the aqueous media in which they are inserted to guarantee those gains. Among the methods applied to produce such composites is the dispersion of CNTs on the surface of anhydrous cement particles using non-aqueous suspensions such as acetone, ethanol, or isopropanol. Even though those non-aqueous media have been individually studied by researchers, comparisons of the efficiency of CNTs dispersion was not found in the literature. Therefore, as a novelty, the present article aims to analyze the influence of the addition of the multi-walled CNTs dispersed in the cited three types of non-aqueous suspensions on the cement paste’s electrical and mechanical properties. Pastes containing 0%, 0.5%, and 1.0% of CNTs were prepared on the surface of anhydrous cement particles using a pre-dispersion technique based on simultaneous sonication and mechanical agitation in the three cited media. Tests to determine electric-volumetric resistivity, compressive strength, and splitting tensile strength were performed. It was observed that acetone dispersion decreases the cement paste’s electrical resistivity, even without the addition of CNTs. The cementitious composites with CNTs demonstrated increased mechanical strength (both compressive and tensile) using all three dispersion media. Statistical analysis (analysis of variance—ANOVA—and Tukey’s Test) was performed to evaluate the significance of the results.

RESUMO O óxido de grafeno tem sido apontado como um material de reforço para compósitos de cimento. Além de ser um material com boa dispersão em água, ele apresenta elevado módulo de elasticidade, elevada resistência à tração, elevada superfície específica e alta condutividade térmica e elétrica. Visando aprofundar o conhecimento acerca do uso do óxido de grafeno em compósitos de cimento, o presente trabalho apresenta uma ampla revisão bibliográfica sobre os efeitos da adição do óxido de grafeno em compósitos de cimento Portland. A metodologia empregada para a seleção dos artigos acadêmicos foi o ProKnow-C, (Knowledge Development Process – Constructivist), ferramenta de revisão literária que permite a evidenciação do estágio atual do conhecimento acadêmico relacionado ao tema de estudo. Por meio desta metodologia de busca e seleção de artigos, foi possível selecionar, a partir de uma amostra bruta de 1354 artigos, os 47 artigos mais relevantes que apresentam as alterações nas propriedades mecânicas, no comportamento reológico e na microestrutura de compósitos de cimento com adição de óxido de grafeno, bem como técnicas de dispersão utilizadas. Dessa forma, as principais conclusões, as lacunas atuais de pesquisa e as oportunidades de estudo foram sumarizadas, constituindo uma base de referência para orientar trabalhos futuros envolvendo o uso de óxido de grafeno para a preparação de compósitos de cimento.

Cement composites prepared with nanoparticles have been widely studied in order to achieve superior performance structures. The incorporation of carbon nanotubes (CNTs) is an excellent alternative due to their mechanical, electrical, and thermal properties. However, effective dispersion is essential to ensure strength gains. In the present work, cement pastes were prepared incorporating CNTs in proportions up to 0.10% by weight of cement, dispersed on the surface of anhydrous cement particles in isopropanol suspension and using ultrasonic agitation. Digital image correlation was employed to obtain basic mechanical parameters of three-point bending tests. The results indicated a 34% gain in compressive strength and 12% in flexural tensile strength gains, respectively, as well as a 70% gain in fracture energy and 14% in fracture toughness in the presence of 0.05% CNTs were recorded. These results suggest that CNTs act as crack propagation controllers. Moreover, CNT presence contributes to pore volume reduction, increases the density of cement pastes, and suggests that CNTs additionally act as nucleation sites of the cement hydration products. Scanning electron microscopy images indicate effective dispersion as a result of the methodology adopted, plus strong bonding between CNTs and the cement hydration product. Therefore, CNTs can be used to obtain more resistant and durable cement-based composites.