Análise dos filmes de passivação formados em aços baixo carbono e microcompósito em função do pH e da força iônica da solução dos poros do concreto: caracterização eletroquímica e por microscopia de força atômica

Abstract

Currently, the growing environmental concern turns on the industry's need to reduce the consumption of natural resources, reduce the generation of waste and reuse the waste generated. In this context, the addition of silica fume and fly ash has shown excellent results, mainly due to the increase in concrete strength. However, the use of these residues causes a reduction in the pH of the concrete pore solution and, consequently, the reduced pH solution can cause the corrosion of the reinforcement. In order to provide resistance to corrosion, most metals or metal alloys have thin and oxidized protective films, called passivation film. Concrete carbonation, caused by burning fossil fuels also reduces the pH of solutions and, consequently, leads to corrosion. Therefore, it is important to understand the role of these additions and carbonation, which can generate large economic losses and volumes of waste in civil construction due to corrosion; and the formation of the film, which has a protective character to reinforcement. This paper characterizes the low carbon steel (LC) and microcomposite steel (MC) passivation film according to the pH variation of the simulated pore solutions. These solutions received the addition of K2SO4 and C6H5K3O7 to correct the ionic strength. The characteristics of the film were studied using cyclic voltammetry, which allowed the identification of the potentials of formation and consumption of the film; galvanostatic cathodic polarization, for calculating the film thickness; and scans with an atomic force microscope, which allowed the evaluation of the film's roughness and elasticity module. From the results obtained, it was observed that the two steels show similar behavior for peak formation, however, the borderline pHs for film formation was different. The reduction in pH caused a decrease in the thickness of the film in both steels. The roughness had the opposite behavior, in the LC steel, the film was more rougher when passivated and this increase proportional to the increase in pH. In the MC steel, the roughness was lower when passivated and the decrease was proportional to the decrease in pH. The elastic modulus in the LC steel reduced associated with pH and, in the MC steel, the behavior pattern was more stable. Finally, all the results show that MC steel has characteristics that confirm its large-scale use in civil construction.