- Demolish and rebuild the structure
- Accept that the anticipated service life duration
may not be reached
- Protect the structure against the ingress of harmful
substances, such as carbon dioxide and chlorides
- Accept that harmful substances can reach the reinforcement,
but protect the reinforcement against
corrosion.
For most projects, the first of the above options will
be undesirable, for obvious reasons. The second option
involves a re-evaluation of the original design parameters
and may in many cases also not be acceptable.
Probably in most cases, the third or fourth option will
be aimed at, i.e. protecting the structure against deterioration
to ensure that the design service life can be
reached. Such methodology may for example include
the application of protective surface coatings or corrosion
inhibitors. Depending on the quality of the structure
(by how much did it not reach the limiting durability
design parameters?), a once-off application may be sufficient,
whereas in other cases a detailed maintenance
plan may need to be established, taking repeated application
of protective measures into account.
The decision of appropriate repair and maintenance
strategies needs to be based on an evaluation
of the expected service life. For this, the measured
durability index value needs to be used as an input
parameter in the service life model, with which the
original design parameter was established. This will
allow an estimation of the actual service life duration
that can be expected. This, in turn, will give the information
of how many years of additional service life
the protective measure needs to provide.
Based on this, it can for example be argued that a
coating, which prevents the ingress of harmful substances
over that required duration, presents a suitable
protective measure, bringing the structure back to its
original service life. However, a clear philosophy
needs to be developed, based on which the design of
appropriate protective measures can be carried out.
The design engineer and the owner of the structure
need to be given clear guidance on what steps to follow
and on what options are available.
From a technical point of view, it needs to be
established, which coatings can be used to either prevent
or slow down the ingress of chlorides or carbon
dioxide sufficiently. The performance of protective
coatings commercially available can commonly be
shown to be promising in short-term tests. However,
there is a lack of data available on the durability of
such coatings. Future research is needed to fill this
gap of knowledge. A current project at the University
of Cape Town is dealing with these issues.
Another promising protection method for reinforced
concrete structures is the application of corrosion
inhibitors. However, also for these materials the
long-term efficiency still needs to be established.