The Constructor

Corrosion Inhibiting Admixtures: Types, Dosages, and Applications

Reading time: 1 minute

Corrosion inhibitors are admixtures that either extend the time to corrosion initiation or significantly reduce the corrosion rate of embedded metal, or both, in concrete containing chlorides in excess of the accepted corrosion threshold value for the metal in untreated concrete, as per ACI 222R.

There are four common type of corrosion inhibiting admixtures, and their dosage is usually dependent upon the client’s expected serviceable life of the structure and on a range of factors that affect the durability of concrete. These include cement type, water-to-cement ratio, cover concrete to the steel, ambient temperature and the expected level of exposure to chlorides

Corrosion-inhibiting admixtures are effective after the concrete has hardened and give a long-term increase in the passivation state of steel reinforcement and other embedded steel in concrete structures.

Why Corrosion Inhibiting Admixtures are Used?

Aggressive substances such as chloride and carbonation could jeopardize passivation layer of iron hydroxides on the steel surface and corrosion would eventually occur.

For these reasons, admixtures that mitigate the corrosion process are useful in extending the life of concrete structures such as highways, multi-storey car parks, jetties, wharves, mooring dolphins, and sea walls.

Types of Corrosion Inhibiting Admixture

The four most common types of corrosion inhibiting admixture are:

1. Amine Carboxylate

Fig. 1: How Protective Layer Absorbed on Reinforced Steel Bars

2. Amine-ester Organic Emulsion

3. Calcium Nitrite

  1. Available as a 30% solution
  2. It is categorized as an anodic inhibitor that interferes with the chloride complexing process by oxidizing the more easily attacked form of iron to the more stable form.
  3. High volume (30 L/m^3) of calcium nitrite is need to achieve desired results.
  4. Calcium nitrite is appropriate to use for reducing chloride induced corrosion of any good-quality concrete, from seawater, salt-laden air, and deicing salt exposure.
  5. It is not applicable for poor-quality concrete or concrete with very low clear cover over the reinforcing steel.
  6. w/c ratio of 0.40 or smaller should be used when calcium nitrite is added to concrete. However, w/c of 0.45 in combination with pozzolan or slag can be used in case of moderate design life concrete construction.
  7. Calcium nitrite is an accelerator of both set and strength development of concrete.
  8. Increase the strength of concrete significantly at early ages especially at 29 days.

4. Organic Alkenyl Dicarboxylic Acid Salt

Exit mobile version