Significant advances have been made in our understanding
of the influence of concrete mixture constituents
on the likelihood and rate of reinforcement
corrosion. Much of this work has focused at understanding
the role of cement extenders and admixtures
in modifying the ionic and fluid transport properties
of the concretes that we use in chloride-laden environments.
Greater understanding of the notion of the
‘threshold’ level of chloride content in relation to the
binder type has also helped to clarify much of the
complexity of empirical data.
Our sense is that continued work is necessary in
developing a more fundamental understanding of the
physico-chemical process related to the interactions
between the products of hydration and corrosioninducing
species such as chlorides or carbon dioxide.
These studies should be focused on ingress, binding
and flow of these materials in concrete. This is necessary
in light of the rapidly changing nature of cementitious
materials that are being used in concrete. Our
reliance on models developed from empirical data,
without fundamental understanding, limits our ability
to predict the long-term performance of new materials
used in concrete. Furthermore, the increasing
use of combinations of supplementary cementitious
materials—so called ternary blends—presents particular
challenges in this context.
The past five years have also seen enormous
growth in the materials and technology of concrete
admixtures. However, there is little information on
the effects of these new materials on the general
durability and deterioration of concrete. In particular,
there is a serious lack of understanding of the effects
of these materials on concrete exposed to the potential
of damage due to reinforcement corrosion.
In the areas of limiting the effects of corrosion of
reinforcing steel, the following are some of the issues
that will require attention:
- Corrosion inhibitors: future research is needed to
establish long-term performance and applicability
- Service life of protective coatings
- The development of corrosion-resistant reinforcement.
There is certainly a need for an international shared
database on long-term performance of concrete
structures in relation to concrete mixture constituents.
This will act as a touchstone for researchers to assess
the suitability of proposed models against a historical
knowledgebase of recorded performance. There is a
special concern here regarding the potential problems
with new materials such as high-performance concrete,
for which long-term behaviour is unrecorded.
In these materials, the likely effects of large amounts
of unhydrated cement on durability (as well as longterm
deformations) remain a concern.