RESUMO A taxa de corrosão instantânea do aço carbono 1040 enterrado em solo, por 6 meses, foi medida por meio da técnica de modulação de frequência eletroquímica (EFM) e pela resistência à polarização linear (LPR). Os resultados foram comparados entre si e com os dados de taxa de corrosão obtidos pela análise de conjuntos de materiais similares e sob mesmo tempo de exposição em campo. Os valores obtidos por EFM foram de (0,088 ± 0,008) mm/ano e, por LPR, de (0,075 ± 0,005) mm/ano. Já, pela perda de massa, foram calculadas variações de espessura deste material, de (0,064 ± 0,016) mm/ano. Assim, nas condições experimentais impostas pode-se inferir que os resultados obtidos pela técnica EFM, serviram para diagnosticar o desempenho do aço carbono 1040 submetido a um processo de corrosão em solo.

ABSTRACT The instantaneous corrosion rate of 1040 carbon steel buried in soil was measured by electrochemical frequency modulation (EFM) and linear polarization resistance (LPR). The results were compared to each other and to the corrosion rate data obtained by the analysis of corrosion coupons exposed in field. The values of instantaneous corrosion rate found in the soil by EFM were 0.088 ± 0.008 mm / year, by LPR of 0.075 ± 0.005 mm / year. The corrosion rate values obtained by weight loss of corrosion coupons were 0.064 ± 0.016 mm / year. Thus, in the experimental conditions imposed it can be inferred that the results obtained by the EFM technique served to diagnose the performance of 1040 carbon steel subjected to a soil corrosion process.

ABSTRACT The addition of nanomaterials to concrete allows structural modifications, improving their properties like mechanical strength and durability. Within these possible nanoscale materials is silica hydrosol (SH). There are many studies highlighting the influence of the surface area of SH particles on the pozzolanic reaction with cement, however little has been studied on the influence of percentage and particle size on the reaction. In this context, the objective of this work was to investigate the influence of the particle size distribution of silica nanoparticles on the pozzolanic reaction in cement pastes, from the comparison of 4 colloidal suspensions. The addition content of these particles, with different sizes, was defined as 3.00% (SH-A), 0.89% (SH-B), 0.77% (SH-C) and 0.32% (SH-D), to equalize the surface areas of all of them, so that the only variables were the percentage and particle size distribution of the silicas. The pozzolanic effect was evaluated by the direct method named Modified Chapelle test, and by indirect methods like Fourier transform infrared spectroscopy (FT IR), and mechanical strength tests. It was concluded that for the same surface area resulting from the addition of SH, the sample that presented the best performance was the CP SH-A, which presented the largest particle size and volume of addition. However, when analysing the relative performance, regarding the concentration of SH added to the paste, the CP SH-D sample obtained the highest mechanical resistance and the highest pozzolanic index. It showed that concentration and particle size, not just surface area, influenced the performance of the nanosilica pozzolanic reaction. The conclusions obtained in the present work allow a better understanding about the addition of SH in cementitious composites and how the content and particle size of such products impact their performance.

RESUMO O encapsulamento de hastes de âncora em pasta de cimento reduz o contato dos materiais metálicos com os ambientes agressivos, em torres estaiadas de linhas de transmissão de energia elétrica. Contudo, ainda são reportados casos de falha prematura devido à corrosão do sistema de ancoragem. O íon cloreto é considerado um dos principais responsáveis pelo início e pela propagação da corrosão. Entretanto, existem muitas divergências em relação a concentração crítica de cloreto no solo e na pasta de cimento e a sua influência na formação dos produtos de corrosão. Neste estudo, o aço carbono 1040 foi exposto em laboratório a ambientes com diferentes concentrações de íons cloreto, 764 e 1764 mg/kg no solo, 2,0% e 3,5% na pasta de cimento, teores estes, baseados nos resultados analíticos obtidos em amostras de hastes e de seu entorno, retiradas do campo. A investigação do estado quanto à corrosão do metal em laboratório foi efetuada ao longo do tempo, pela medida do potencial de circuito aberto (OCP- “Open Circuit Potential”) e pela espectroscopia de impedância eletroquímica (EIE). Os produtos de corrosão foram caracterizados por microscopia eletrônica de varredura, com análise química elementar (MEV/EDS) e difração de raios-X (DRX). Por meio da análise de EIE foi possível detectar a evolução do processo corrosivo do metal no solo e na pasta de cimento, mesmo sendo observadas diferentes formas de corrosão: generalizada no primeiro e localizada nesta última, respectivamente. Na avaliação dos produtos de corrosão, por MEV e DRX, foi inferida a presença de goetita, e calcita na superfície do aço exposto ao solo, e no encapsulado em pasta cimento foi possível visualizar os pites formados e as composições do seu entorno superficial. Esses resultados indicaram a necessidade da utilização de metais mais resistentes à corrosão em ambientes com íons cloreto, visando o aumento da durabilidade do sistema de ancoragem.

ABSTRACT The encasement of anchor rods in cement paste reduces the contact of metal materials with aggressive environments in guyed power transmission line towers, however, many cases of premature failure due to corrosion of the anchorage systems are still reported. Chloride ions are considered to be one of the main factors responsible for the initiation and propagation of corrosion, however, there are many differences regarding the critical concentration of chloride in the soil and cement paste and their influence on the formation of corrosion products. In this study carbon steel 1040 was exposed in the laboratory to environments with different concentrations of chloride ions, 764 and 1764 mg/kg in the soil, 2.0% and 3.5% in the cement paste, based on the analytical results obtained in samples of rods and their surroundings, taken from the field. The investigation of the corrosion state of the metal in the laboratory was evaluated, over time, by the measurement of open circuit potential (OCP), electrochemical impedance spectroscopy (EIS). The corrosion products were characterized by scanning electron microscopy with elemental chemical analysis (SEM/EDS) and X-ray diffraction (XRD). By means of the EIS analysis, it was possible to detect the evolution of the corrosive process of the metal in the soil and cement paste, even though different forms of corrosion were observed: general in the soil and localized in the cement paste. Moreover, the evaluation of the corrosion products, by SEM and XRD, indicated the presence of goethite and calcite on the steel surface exposed to the soil, and in the steel encapsulated in cement paste it was possible to visualize the pits formed and the compositions of their surface surroundings. These results suggest to need to use corrosion resistant metals in environments with chloride ions, in order to increase the durability of the anchorage system.