Corrosion inhibitors are one of a variety of techniques that can be employed in an effort to suppress and control the rate of steel corrosion in concrete structures.

This page presents a general description on applying Corrosion Inhibitors.  Incorporated within the page is also a tool to calculate the total cost of applying Corrosion Inhibitors.

Certain factors has to be taken into consideration to check if Corrosion Inhibitor is suitable for the structure in question.  

Refer to Section 7 of the guidance document  to provide more guidance on the selection of corrosion inhibitor for concrete.

The Check List tool present a list of criteria which should not exist within the structure, if Corrosion Inhibitor  is to be used.

If any of the criteria is checked, then it is our recommendation that it should not be applied.

Activate this tool, Corrosion Inhibitor  to calculate the cost of using  Corrosion Inhibitor.

The two main inputs expected are the 'Cost of Technique'  and 'Area to be Treated'.   The cost relating to the technique can be found by activating the Costing link within the tool.

Multiplication of the two main inputs generates a total cost for the specified technique.  This cost is then added to the 'Fixed Cost' to produce a total cost for applying the technique from conception to finish.

The first and last three inputs which are the'Name of the Technique',  'Maintenance Cost' ,    'Life of Technique' and 'Life of Retreatment' are essential if the user requires the output generated by this tool for future reference.

The generated output is presented in a report format which contains the specified technique as well as other details relating to the calculation .

The output produced within the Total Cost text area can then be copied and pasted within a report or a document for future reference .

It is possible to divide concrete corrosion inhibitors into two generic categories.

·         Concrete admixture inhibitors - used as a preventative measure.

·         Surface applied and drilled-in inhibitors - used as a curative or preventative measure.

These two generic categories can be further subdivided into anodic, cathodic and ambiodic (mixed) inhibitors depending upon the formulation of the inhibitor.

Nitrite based corrosion inhibitors:  Anodic cast-in admixture

These are categorised as anodic inhibitors and generally cast into the mortar/concrete to delay the onset of further corrosion.

Monofluorophosphate based corrosion inhibitors: Anodic surface applied

Manufacturers of monofluorophosphate (MFP) based corrosion inhibitors claim that most of the product dissociates in aqueous solution. 

It is claimed that the PO₃F^2- ion provides an inhibiting action against the corrosion of reinforcement steel.  X-ray photoelectron spectroscopy analysis (XPS) of the steel surface has shown that the passive oxide film formed on the surface of the steel in alkaline conditions becomes reinforced and more resistant to aggressive ions when MFP is present around the steel reinforcement.

Other studies on fully carbonated mortar samples, submitted to conditions that promote the development of corrosion products on the surface of the steel, have shown that treatment with MFP solution can slow down the rate of the corrosion process.

Studies have also claimed that within the outer few millimeters of the concrete, MFP reacts with calcium hydroxide and calcium carbonate formed during the carbonation process to develop fluoroapatite minerals. It is claimed that the formation of these minerals has little effect on the concrete porosity or vapour transmission through the concrete. However, the formation of apatite minerals leads to an increase in the resistance to freeze/thaw scaling, even when the concrete is contaminated with chloride.

Alkanolamines and amine based corrosion inhibitors: 

Anodic/cathodic surface applied impregnations

Manufacturers claim that the latest liquid multi-functional concrete corrosion inhibitors provide both anodic and cathodic inhibition by adsorption at the steel/concrete interface. Such synergistic inhibitors are based on an organic and inorganic film-forming blend of amino compounds that diffuse through the concrete in both a liquid and vapour phase. The adsorbed layer formed by the corrosion inhibitor is typically in the order of 0.01mm to 0.1mm in thickness. However, since there are several propriety blends from different manufacturers it is difficult to discuss the functionality of this group of corrosion inhibitors in anything but general terms.