Chemical admixtures - Concrete Mix Design, Quality Control and Specification - page 85

Figure 4.3 One of Edison's concrete houses under construction in 1919.
4.3.10 Corrosion inhibitors
As most durability problems in concrete are related to chloride-induced
corrosion of embedded reinforcement, it is not surprising that admixtures
would be developed to increase the chloride threshold level. Although
there are many chemicals that have corrosion inhibiting properties, there
are basically four generic types commercially available: calcium nitrite,
amine carboxylate, amine-ester organic emulsion, and organic alkenyl
dicarboxylic acid salt.
Apparently sodium nitrite was used by the Germans to reduce the cor-
rosive effects of calcium chloride, which was used as an accelerator when
constructing the infrastructure to mount the Blitzkrieg at the start of
WWII. However, sodium nitrite tends to reduce strength. In the 1980s, the
company WR Grace began marketing calcium nitrite as an anodic inhibitor
and it is the most widely used material today. Calcium nitrite is also an
effective accelerating admixture.
There are examples of long-term corrosion resistance using calcium
nitrite. Some concerns exist over the increased cracking potential of con-
crete containing large quantities of calcium nitrite due to the increased
shrinkage and temperature rise. Montes et al. (2004) showed that the effect
of calcium nitrite on corrosion inhibition in cracked elements was limited,
presumably due to its lower resistivity. Ann et al. (2006) showed that this
lower resistivity tended to offset some of the benefit of the inhibitor.
Amine carboxylate admixtures were developed from vapour phase
inhibitors, which have a long history of use in other industries. The initial
applications for reinforced concrete were based on surface treatment and