A MATHEMATICAL-MODEL FOR ELECTROCHEMICAL REMOVAL OF CHLORIDE FROM CONCRETE STRUCTURES

An examination of the literature suggests that the electrochemical rem oval of chloride (ECR)from reinforced concrete is affected strongly by chloride binding (i.e., by removal of chloride from the pore solution as the result of interaction with the hydrated cement). A mathematica l model of the chloride removal process was developed that incorporate s a term describing the rate of release of bound chloride. The predict ed quantities of chloride removed correlated well with those observed in practice. Using the model, ECR can be approximated by a two-stage p rocess. Initially, the free chloride is removed at a rate that depends upon the concrete resistivity, chloride diffusion coefficient, concre te cover, current density, and initial chloride profile. The amount of chloride remaining at the end of the first stage is determined by the quantity of bound chloride. The process subsequently is dominated by the rate of release of bound chloride. A first order rate constant cha racterizing this process, with a value of 3.7 x 10(-8) /s to 5.1 x 10( -8) /s, was identified for the concretes studied. The model was shown to be a useful engineering tool that can be used to optimize the appli cation of ECR.