Carbonation, neutralization and reinforcement corrosion for concrete in long-term atmospheric exposures

This paper presents observations of carbonation and alkali loss for well-compacted reinforced concrete columns from the exterior and the interior of a 60 year-old in-land building. Calcium carbonate formation was detected only in the outermost 10-15 mm. However, alkali loss and concrete pH reduction extended much further inwards but reinforcement corrosion was not observed. Theoretical thermodynamic conditions dictate that corrosion initiation of reinforcement can result only from the long-term dissolution and loss by leaching of calcium hydroxide from the concrete matrix. These appear rate-limited by the barrier effect of carbonated concrete. These interpretations provide a new model for 'carbonation' initiation of reinforcement corrosion. The results also show the potential for concretes to absorb atmospheric carbon dioxide (green-house gases) for extended time without significant risk of reinforcement corrosion.