Typical Potential Range; Factors Affecting The Potential Measurement - Proceq PM8500 User Manual

Profometer corrosion

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Figure 3: Measuring principle.

3.1.2 Typical Potential Range

Typical orders of magnitude (for information only) for the half-cell potential of steel in concrete

measured against a Cu/CuSO4 reference electrode are in the following range (RILEM TC 154-

EMC):

water saturated concrete without O2

moist, chloride contaminated concrete

moist, chloride free concrete

moist, carbonated concrete

dry, carbonated concrete

In general terms the probability of corrosion rises with low (negative) potentials; active

corrosion can be expected at locations where a negative potential is surrounded by

increasingly positive potentials, i.e., locations with a positive potential gradient. Potential

differences of around +100mV within a 1m measurement area, together with negative

potentials can be a clear indication of active corrosion.

The actual potential absolute value (corrosion threshold) below which active corrosion can be

expected may vary significantly on different structures. It is however useful to mention the

thresholds suggested by ASTM C 876-22b, Appendix X1, assigning a 90% probability of

corrosion ongoing to the areas more negative than -350 mV, and a 90% probability of no

corrosion to the areas more positive than -200 mV, judging uncertain the behavior in the

regions in between the two thresholds. Be sure to note the conditions stated by ASTM as to

the applicability of these threshold values.

Provided that the corrosion conditions are equal (chloride content or carbonation of the

concrete at the steel surface) the main influences upon the half-cell potentials are:

25. September 2023

-1000 to -900 mV

-600 to -400 mV

-200 to +100 mV

-400 to +100 mV

0 to +200 mV

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