Chemical admixtures - Concrete Mix Design, Quality Control and Specification - page 86

the expectation of migration to the reinforcement. This always seemed a bit
doubtful in better quality concrete with reasonable cover. Molecules would
be expected to take the easy option of dissipating into the air rather than
the tortuous journey through the dense concrete matrix. However, they do
bond tenaciously to reinforcing steel. The supplier can test whether surface
application will be effective. As an admixture, however, it does seem to
have a number of advantages. It is both an anodic and cathodic inhibitor,
which is useful in both new construction and repair applications. It does
not detrimentally affect the fresh or hardened properties of the concrete,
but there is some retardation. Recent data from a bridge deck in Minnesota
that was poured in 1986 demonstrates a significant reduction in corrosion
rate in a good quality concrete.
Both amine-ester organic emulsion and organic alkenyl dicarboxylic acid
salt act as water resisting admixtures and therefore it is difficult to assess
their claims to be corrosion inhibitors as the test procedures to demonstrate
their performance normally involve penetration of waterborne chlorides
followed by corrosion initiation and propagation.
4.3.11 Workability retaining
Workability retaining admixtures are added separately to concrete that
may already contain a water reducing or HRWR admixture. These admix-
tures extend the time that concrete can be workable without affecting
subsequent setting time or early compressive strength development. The
polymers within these admixtures are slowly released coating the surfaces
of the cement particles preventing agglomeration and stiffening. They are
a useful tool to tailor concrete for particular applications without going
to the extent of using hydration controlling admixtures, which would be
better suited for prolonged delay in setting and reactivation.