Effect of initial curing on chloride diffusion in concrete repair materials

This paper presents the results of an experimental investigation on the effect of initial curing on chloride diffusion in three generic repair materials and a concrete mix of similar grade. Two field conditions of initial curing were simulated as follows: (1) exposure to a chloride environment after 24 h of casting to simulate repair situations, for example in the tidal zone of marine structures where repairs cannot be protected from tidal exposure for long periods; and (2) 28 days of curing at 20 degrees C, 55% relative humidity to simulate field conditions where the repair patches art: exposed to the ambient environment without any prolonged protected curing. For comparison purposes identical specimens were cured in water at 20 degrees C for 28 days before exposure to the chloride environment. Chloride concentration profiles in the materials were determined after 28, 90, and 180 days of exposure. Regression analysis of the experimental data was carried out applying Fick's second law of diffusion to determine the diffusion coefficients (D-C) and chloride concentration on the surface (C-0) Based on the results obtained, an analytical expression for the long-term prediction of chloride concentration in repair materials is given. The results show a high rate of chloride diffusion in the cementitious repair materials containing polymer latex additives relative to plain concrete. The effect of inadequate initial curing on chloride penetration (e.g., exposure to chlorides after 24 h of casting or 28-day air curing) is mole pronounced in concrete mixes than in generic repair materials. (C) 1999 Elsevier Science Ltd. All rights reserved.