Finite Boundary Conditions Due to the Bar Presence in the Model of Chloride Penetration

Abstract

The chloride penetration is usually modelled through the application of a solution of Fick’s second law of diffusion, based on the assumption of semi-infinite boundary conditions. However, the presence of the bars, on whose surface the chlorides accumulate, makes this assumption incorrect. As the time progresses, the chlorides in the steel/concrete interface increase in concentration more than the chlorides overpassing the bar position without obstacles. This circumstance, although previously studied, has not been introduced in common practice, in spite of it supposes early reaching of the chloride threshold. The study in this paper shows a deterministic analysis of the chloride diffusion process by the finite element method (FEM) which numerically solves Fick’s second law, taking into account the accumulation of the chlorides on the bar surface. Several examples are calculated and factors between the finite/semi-infinite solutions are given. These factors depend on the cover depth and the diffusion coefficient, and with less importance, on the diameter of the bar, which make it unfeasible to propose a general trend.

Special Issue: Structural Concrete Material—New Trends for Eco-Efficiency and Performance

“…Tavares and Andrade [ 7 ] demonstrated that the usual modelling of chloride penetration, based on Fick’s second law of diffusion, is significantly affected by the presence of reinforcements. In this case, the assumption of semi-infinite boundary conditions is no longer valid, and the chloride concentration at the reinforcement depth becomes higher than that estimated from Fick’s second law.…”