Corrosion rate measurement by Half-cell potential

The half-cell potential measurement is an electrochemical technique commonly used by engineers to assess the severity of corrosion in reinforced concrete structures.

Corrosion of steel reinforcement is a major factor in the deterioration of highway and bridge infrastructure. A survey of the condition of a reinforced concrete structure is the first step towards its rehabilitation. A rapid, cost-effective and non-destructive condition survey offers key information on the evaluation of corrosion, and aids in the quality assurance of concrete repair and rehabilitation and in the prediction of remaining service life.

 

                       Schematic showing basics of the half-cell potential measurement technique

 

Traditional way to assess the severity of steel corrosion is to measure the corrosion potential, since it is qualitatively associated with the steel corrosion rate. One can measure the potential difference between a standard portable half-cell, normally a copper/ copper sulphate (Cu/CuSO4) standard reference electrode placed on the surface of the concrete with the steel reinforcement underneath. We have developed use of standard calomel reference electrode[ at almost fraction of cost]  available in our lab as  illustrated above. The reference electrode is connected to the negative end of the voltmeter and the steel reinforcement to the positive.

    Half cell potential reading      Corrosion activity
>-80 mv Low risk of corrosion{10 % risk}
-80 mv to -230 mv Intermediate corrosion risk
<-230 mv High corrosion  risk {90 % risk}
<-380 mv Severe corrosion

      

         Criteria for corrosion of steel in concrete for calomel reference electrode

 

A more negative reading of potential is generally considered to indicate a higher probability of corrosion. However, this general “rule” may not always apply because of the complexity of today’s concrete and repair technologies. eg Not directly applicable to epoxy coated & galvanized bars

It must be stressed that the half-cell potential measurement only reveals the corrosion probability at a given location and time. Long-term monitoring of the half-cell potential reading is more meaningful.

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