ABSTRACT
Depending on the resistance of the concrete against chloride penetration and the thickness of the concrete cover, it may take many years before the chlorides reach the embedded steel. After the chlorides have reached the steel and the corrosion process starts, however, it may take only a few years before visual damage in the form of cracks and rust staining appears, but it may take a long time before the load-carrying capacity of the structure is severely reduced. Schematically, this deteriorating process takes place as shown in Figure 6.1. As soon as the corrosion process starts, a very complex system of galvanic cell activities develops in the concrete structure, as previously discussed in Chapter 3. In this system of galvanic cell activities, the deterioration appears in the form of concentrated pitting corrosion in the anodic areas of the rebar system, while the adjacent
cathodic areas act as catchment areas for the oxygen. Although larger portions of the rebar system eventually become depassivated, all of these areas will not necessarily corrode. As also discussed in Chapter 3, the steel in the first and most active corroding parts of the structure will act as sacrificial anodes and thus cathodically protect other parts of the structure. Since both the structural shape and the local environmental exposure will affect this pattern of deterioration, it appears to be very difficult to develop a general mathematical model for predicting the time necessary before the load-carrying capacity of the structure as a whole becomes severely reduced. Although several attempts at developing such a mathematical model have been made (Lu et al., 2008), it appears that no reliable mathematical model for this very complex deteriorating process currently exists. Already in the early 1970s, however, Collepardi et al. (1970, 1972) came up with a relatively simple mathematical model for estimating the time necessary for the chlorides to reach the embedded steel through concrete of a given quality and thickness.
