IMPEDANCE STUDY OF REINFORCING STEEL IN SIMULATED PORE SOLUTION WITH TANNIN

Voltammetric and electrochemical impedance spectroscopy (EIS) measurem ents were performed to study the corrosion behavior of reinforcing ste el in a simulated concrete pore solution with the addition of chloride anions and mimosa tannin. Surface films were analyzed with Auger elec tron spectroscopy. Under open-circuit conditions, in chloride-containi ng solutions, tile charge-transfer resistance (R(ct)) decreased after prolonged immersion, whereas the interfacial capacitance (C-if) and th e semicircle depression angle increased. These changes were ascribed m ainly to redox reactions involving Fe(II)/Fe(III) species and to the b uildup, of corrosion products. An addition of tannin slowed down the c hanges in R(ct) and C-if. In the presence of tannin, the surface films were much thinner than those in the tannin-free solutions and contain ed probably a tannin-Fe(III) chelate at the outer surface. It is sugge sted that the impedance data for corroded reinforcing steel provide in formation on the accumulation of corrosion products rather than on the instant corrosion rate of the steel.