Modeling and simulation on coupled chloride and calcium diffusion in concrete

Abstract

Permanently exposed to the chloride-contained water environment, concrete structures are subjected to a complicated interaction between chloride attack and calcium leaching, which can be described by the coupled chloride and calcium diffusion in concrete. Based on the mechanism of coupled chloride attack and calcium leaching on concrete, this paper proposes a series of equations for modeling their coupled diffusion, and they were numerically solved by an implicit finite difference scheme. Via verification, this model is used to numerically simulate the coupled chloride and calcium diffusion in a concrete plate, characterized by calcium concentration in pore solution, porosity, and chloride content in concrete, etc. Results show that calcium leaching increases the concrete porosity and chloride diffusivity, and chloride attack can accelerate the leaching process of concrete. Free chloride content in pore solution increases with the leaching time, and it is obviously lower under single chloride attack than that under the coupled chloride attack and calcium leaching. The decalcification of C-S-H gel and decomposition of Kuzel’s and Friedel’s salts caused by leaching can reduce the bounded capacity of concrete on free chlorides, and it leads to a decrease in the bound chloride content in concrete.