Re-alkalinization of carbonated concrete by means of alkaline migration

In Belgium, a number of girder bridge deck slabs have over the past several years been displaying major degradations (delamination, disaggregation, etc.) capable, in time, of leading to slab perforation. This form of degradation, called "rotting of bridge deck slab concrete" is not uniformly distributed over the deck surface: deteriorated zones can be distinguished from intact zones and moreover are often associated with the presence of dark spots. On the lower surface of some such spots, the previously-carbonated concrete layer can sometimes once again display a pH of above 8.3. It will also be demonstrated that this anomaly may be attributed to a migration of alkaline through the concrete slab towards the lower surface, thereby causing a re-alkalinization of the carbonated layer and hence a rise in pH.