The protection afforded to steel by the normally passive environment of concrete can be compromised by the introduction of various amounts of chloride ions. It is generally recognized that a large depression in the half-cell potential (or Ecorr) of steel in concrete can be indicative of this passive/active transition. The transition potential is between −0.220 and −0.350 V vs SCE (saturated calomel electrode).1,2 The shift to active potential is thought to be associated with the attainment of a critical amount of chloride at the surface of the steel.
Steel distress has been noted when the half-cell potentials are more negative than −0.350 V vs SCE and when chloride values are greater than 0.2 g Cl/g cement (1.3 lbs Cl/yd3 or 330 ppm on a concrete basis).2,3 These values are determined from chloride analysis of cores taken near the surface of the steel, and the establishment...
