Chloride Binding Capacity in Cement‐Fly‐Ash Pastes

The capacity to bind chloride ions in hydrated cement paste, with and without fly ash, is studied. Free chloride ions remaining in the pore solution are determined. The hardened pastes are exposed to continuous fog curing, moderate or CO2 polluted environments. Long initial curing of fly‐ash cement pastes, which were to be subjected to moderate environment of negligible carbonation, are found essential in order to make use of the fly‐ash capacity to trap chloride ions. However, fly‐ash pastes that are to be eventually subjected to a CO2 polluted environment show a much lower capacity to trap the chloride ions than the pastes that do not incorporate fly ash. In these fly‐ash cement pastes, larger release of the chloride ions to the pore solution is associated with longer initial curing periods. In elements of structures where chloride contamination is anticipated and where carbonation is likely to proceed rather quickly, the corrosion of steel reinforcement is expected. The results found in this research indicate that due caution must be exercised when setting the minimum cover to reinforcement, curing conditions, and coating measures in the event of using fly‐ash concrete in structural elements.