Civil Engineering Reference
In-Depth Information
The protection of the reinforcement therefore depends on the prevention
of diffusion of carbon dioxide, and in some environments, such as bridges,
chloride salts.
The type of corrosion which occurs varies. Carbonation-induced
corrosion tends to affect large areas of the bar, causing a gradual loss of
section over a relatively wide area. The corrosion problem is obvious before
serious damage can be done because the concrete cover will spall. With
chlorides, a different mechanism often occurs, causing very localised severe
loss. An example of corrosion caused by both carbonation and chloride is
given in
Figure 1.9.
This can occur without disruption of the cover concrete
and almost total loss of section can occur before problems become apparent
at the surface. Where pre-stressed steel is used, catastrophic failures have
occurred with no prior warning, even on a structure which had been load
tested shortly before the failure occurred!
Figure 1.9
illustrates corrosion caused by both carbonation and ingress of
wind-blown marine salt to an office structure near to the sea. Interestingly,
we had surveyed the same structure three years previously, and only splitting
of the columns was apparent. In three years the damage had progressed
to become a public safety matter, and was verging on causing structural
problems.
