Recent observations derived from actual structures show that compared to other concretes, concretes containing high levels of carbonates (such as limestones and dolomites) tend to have longer reinforcement initiation times and also much longer durations before the occurrence of active corrosion causing obvious damage. This is provided that the structures do not suffer from poor workmanship, alkali reactions or other failure mechanisms. These findings are reviewed and a small number of additional examples given. The observations are consistent with careful laboratory experiments available in corrosion science literature. However, they are not consistent with the conventional wisdom that associates reinforcement corrosion initiation with the formation of calcium carbonate within the concrete matrix, such as caused by the influx of carbon dioxide from the environment. To cause initiation other processes, such as alkali leaching, must occur to lower the pH to around 8.5 or lower. Only this level of pH is consistent with electrochemistry fundamentals for initiation of steel corrosion. These observations have implications for achieving durable concrete structures.
Australian Journal of Structural Engineering Vol. 10, Issue 3, p. 215-226