Influência de nanotubos de carbono (NTC) na durabilidade do concreto quanto à ação de cloretos

Abstract

In the last decades, the use of nanotechnology has grown in several sectors, being incorporated in cement-based matrices. Among the different types of nanomaterials, carbon nanotubes (CNT) have been used in several kinds of research. Due to the difficulties in dispersing CNTs in water, there is a need to use alternative techniques to obtain homogeneous matrices. Recent studies show the beneficial effect of CNTs when added to the cement matrix. However, few address the durability of these matrices, especially regarding the corrosion of steel embedded in concrete with CNT. The present work analyzed the influence of the use of CNT on the properties of cementitious matrices, suggesting the multicriteria analysis as an alternative, simple and effective technique that aims to obtain the optimal content of additive to disperse CNTs. Subsequently, the effects of these nanoparticles on the corrosion phenomenon in reinforced concrete were evaluated. Thus, techniques were used to evaluate the durability of cementitious matrices through chloride migration tests, corrosion potential, electrochemical impedance spectroscopy (EIE), and electrical resistivity. The multicriteria analysis indicated that the CNT was dispersed more efficiently when using 0.10% additive based on polycarboxylate by mass. The mortars showed an increase of up to 41% in flexural tensile strength, with the incorporation of 0.075% of NTC (considered ideal), in mass, with less expressive improvements (up to 19%) when evaluating the flexural traction of concretes with NTC. The presence of CNT promoted a significant reduction in the electrical resistivity of the concrete due to the high conductivity of this material. However, the chlorine ion migration test indicated that the non-stationary diffusion coefficient was reduced, causing an increase in the useful life by up to 52%. Furthermore, the corrosion potential and EIE tests indicated that the densification caused in the matrix due to the use of CNT has a preponderant effect on the protection capacity of the steel, with a behavior that is minimally similar to the reference concretes, allowing a reduction in the corrosion rate of 150 to 64 µm/year.