Chloride penetration in concrete with trilinear binding isotherm

Chloride binding in concrete is an important factor and it can significantly affect the penetration speed of chlorides in concrete and thus the service life of concrete structures. In this paper a new chloride binding isotherm is proposed to be included in the diffusion model of chlorides in concrete. Instead of the use of the traditional Freundlich or Langmuir isotherm, the present chloride binding model uses a trilinear function to describe the chloride binding in concrete. The trilinear binding isotherm not only reflects the nonlinear binding feature of chlorides in concrete when it is exposed to a chloride environment, but also makes it possible to achieve an analytical solution of the chloride diffusion equation. In the present paper, the superior of using trilinear binding isotherm to other binding isotherms is demonstrated. The detailed derivation of the analytical solution of the chloride diffusion equation with nonlinear binding feature is described and illustrated. To demonstrate the rationality and accuracy of the analytical solution derived, comparisons between the analytical solution and the numerical solution and experimental results are also provided. It is shown that the chloride diffusion profiles obtained from the chloride diffusion equation with the trilinear binding isotherm are much closer the experimental results than that obtained from the chloride diffusion equation with linear or bilinear binding isotherm.