AN ELECTROCHEMICAL INVESTIGATION OF THE CORROSION OF STEEL IN CONCRETE (POTENTIODYNAMIC TESTS, SALT, CHLORIDE, PITTING SCAN, REST POTENTIAL)

The corrosion of steel in concrete was studied by means of potentiodynamic curves, potentiostatic plots and pitting scans. About 450 cylindrical reinforced concrete specimens were subjected to continuous or alternating immersion in solutions of varying concentrations of salt followed by electrochemical testing. In addition, similar electrochemical tests were performed on bare steel in a simulated pore solution containing various amounts of salt. The simulated pore solution was made up of saturated Ca(OH)(,2) containing 0.6M KOH and 0.2M NaOH and the salt was added after passivity was established. It was determined that the free corrosion potential, or E(,corr), is a better indicator of corrosion activity than the time of exposure to salt solutions. The effects of a passive/active transition were reflected in the potentiodynamic curves, potentiostatic plots, and pitting scans as well as the chemical analysis of water-soluble chloride remaining on the bars after removal from the concrete.;Based on the electrochemical testing, the chemical analysis, and the SEM identification of definite microcells on the steel bars, the time for depassivation, as determined by Bazant in his physical model for steel corrosion in concrete sea structures, was modified. It was shown that the time for depassivation is a function of the time to reach a chloride threshold as well as the oxygen diffusivity and the cathode/anode ratio.