Contribuição ao estudo da corrosão em estruturas de concreto através da determinação do coeficiente de difusão do íon cloreto usando movimento browniano

Abstract

Chloride ion transport is important for predicting the durability of reinforced concrete structures. For this purpose, the prediction of chloride ion penetration, the prediction of diffusion and tortuosity for porous structural materials improves the definition of structural useful life. The diffusion coefficient influences the transport of chloride ions, which can cause corrosion of structures. This work proposes the definition of the diffusion coefficient due to Brownian motion. Models were suggested to determine the chloride ion diffusion coefficient. In the research, the Stokes-Einstein diffusion equation was used as a reference. Its combination with the Langevin diffusion equation and the Einstein relationship provided the opportunity for other diffusion equations to determine other parameters such as tortuosity, concentration, and penetration of the chloride ion for a period of up to 10 years. Thus, two suggested paths for carrying out Brownian motion emerged: one considering two types of correction in the mean square of the Brownian displacement when using Langevin’s equations and Einstein’s relationship and another path where the correction occurs in the combination of the equations of Stokes-Einstein diffusion, Langevin and Einstein relation to determine the diffusion to later implement the Brownian movement. These suggestions prevent the numerical value of tortuosity, due to slow diffusion, from being greater than that found with the reference equation. A representative volume element was considered, and the tortuosity of the pores could be determined. Scanned images were used to reconstruct the 3D representative element where, in its porous network, simulations were carried out at different starting points of the chloride ion particles to check whether there would be differences in the value of the diffusion coefficient and tortuosity. The differences only occurred when using the diffusion equations without the necessary corrections and not due to the location of the starting point of the Brownian movement.