These include cement type, water-cement ratio, covering concrete versus steel, ambient temperature and expected chloride exposure levels. A typical dosage range for a 30% calcium nitrite solution is 10-30 L/m3, but a more common range is 10 to 20 L/m3. Amino alcohol-based corrosion inhibitors are usually used in an amount of 3 to 4% by volume based on the weight of the cement. Both types can be used with other admixture types and it is often recommended that they be used with high-efficiency water reducing admixtures to ensure the quality and durability of the base concrete.
The mechanism by which corrosion inhibitors work depends on their chemical nature. Calcium nitrite-based corrosion inhibitors convert the passive layer on the steel surface to a more stable, less reactive state. When the chloride ions reach this layer, no reaction occurs - the steel is passive. It is the anodic corrosion site that protects steel from chloride attack, so nitrite is called anodic inhibitor.
Calcium nitrite reacts with oxygen and converts to calcium nitrate when some oxygen ions penetrate the concrete. However, when all the calcium nitrite added during mixing has been converted to calcium nitrate, the attack of the oxygen ions on the reinforcement resumes. Therefore, adding some calcium nitrite to concrete can only provide additional protection against corrosion of steel reinforcement, not permanent protection. However, this additional protection is very interesting in the case of low water-cement ratio concrete, which already provides a high resistance to oxygen penetration in the concrete. For example, the city of Montreal systematically adds some calcium nitrite to the high-performance concrete used to build downtown infrastructure because repairs are complex, expensive and cause traffic congestion.
Calcium nitrite was pioneered in Japan169 and was offered as a stable solution containing up to 40% dissolved solids in the 1970s and was immediately used as an accelerator. Multiple studies have also confirmed that this chemical prevents pitting corrosion in steel exposed to chlorides in alkaline environments. 170,171 The mechanism by which this protection occurs can be described as anodic inhibition.
Sodium nitrite and calcium nitrite have the functions of lowering the freezing point, accelerating hardening, and anti-corrosion. The general dosage is 1% to 8%.
The Cl-/NO2- concentration ratio in the pore fluid is as high as 1.0~1.5, and the Cl-/OH- ratio is in the range of 0.27~0.57.174,175. Calcium nitrite can prevent the pitting of steel bars in concrete. There is also evidence that the crack width on the surface In carbonized or cracked concrete < 0.2 mm, the admixture is effective in protecting the steel. 176,177

Calcium nitrate has also been shown178,179 to act as an anodic inhibitor against chloride-induced corrosion of rebar, with a mechanism of action similar to that of calcium nitrite. combined reduction half-reactions.