Actions during service 167
phase is defined as the end of the service life of the concrete structure,
and no active corrosion at all is accepted. On the one hand, this approach
is often justified because the propagation time is typically much shorter
than the initiation time (in the case of appropriate design and execution
of the structure). On the other hand, it seems somewhat too conservative
in general to define the end of service life before any real damage occurs.
However, it is also important to be aware that most corrosion problems in
real concrete structures occur due to insufficient concrete quality and/or
insufficient cover thickness, substantially reducing the initiation time (see
also Sections 5.4.2 and 5.4.3). Thus, it seems justified to focus indeed on
the initiation time, duly including quality assurance procedures to make
sure that the as-built structure meets the designed properties (concrete
quality, concrete cover). Keeping the reinforcing steel passivated during the
entire service life is a good and safe design approach, but appropriate quality procedures are also needed during execution to make sure that design
conditions are reached in practice.
Referring again to the Pourbaix diagram, it could be concluded that
bringing the steel reinforcement into an environment with a higher alkalinity is an efficient measure to prevent corrosion. The fortunate situation
in case of reinforced concrete is that this kind of alkaline environment is
automatically provided by the hydration process of the cement. However,
as already mentioned and as will be detailed further on, the protective passivating layer can be attacked due to external actions. Other, more active
corrosion control measures can be applied based on the information given
in the Pourbaix diagram. While not changing the pH value (around 7),
Time
Propagation
Initiation
CO 2
H 2 O
O 2
Cl
–
Critical corrosion value (acceptance level)
Service life
Corrosion
Figure 5.40 Phenomenological evolution of the corrosion process of reinforcing steel
in concrete.
phase is defined as the end of the service life of the concrete structure,
and no active corrosion at all is accepted. On the one hand, this approach
is often justified because the propagation time is typically much shorter
than the initiation time (in the case of appropriate design and execution
of the structure). On the other hand, it seems somewhat too conservative
in general to define the end of service life before any real damage occurs.
However, it is also important to be aware that most corrosion problems in
real concrete structures occur due to insufficient concrete quality and/or
insufficient cover thickness, substantially reducing the initiation time (see
also Sections 5.4.2 and 5.4.3). Thus, it seems justified to focus indeed on
the initiation time, duly including quality assurance procedures to make
sure that the as-built structure meets the designed properties (concrete
quality, concrete cover). Keeping the reinforcing steel passivated during the
entire service life is a good and safe design approach, but appropriate quality procedures are also needed during execution to make sure that design
conditions are reached in practice.
Referring again to the Pourbaix diagram, it could be concluded that
bringing the steel reinforcement into an environment with a higher alkalinity is an efficient measure to prevent corrosion. The fortunate situation
in case of reinforced concrete is that this kind of alkaline environment is
automatically provided by the hydration process of the cement. However,
as already mentioned and as will be detailed further on, the protective passivating layer can be attacked due to external actions. Other, more active
corrosion control measures can be applied based on the information given
in the Pourbaix diagram. While not changing the pH value (around 7),
Time
Propagation
Initiation
CO 2
H 2 O
O 2
Cl
–
Critical corrosion value (acceptance level)
Service life
Corrosion
Figure 5.40 Phenomenological evolution of the corrosion process of reinforcing steel
in concrete.