The effect of steel fiber (SF) addition to concrete on the corrosion behavior of steel reinforcement was studied by immersion corrosion tests in a 3mass% NaCl solution for 363 days. The tests were conducted on steel rod/mortar specimens with different SF content (0-2vol%), and corrosion potentials and electrochemical impedance of the specimens were measured during the tests. Corrosion potentials of the specimens were not so changed by the SF content. Electrochemical impedance measured at corrosion potentials was analyzed to get charge transfer resistance (Rct) using an equivalent electrical circuit with the Rct, Warburg impedance and a constant-phase element. The corrosion rate of steel rod in mortar estimated from the reciprocal of the Rct decreased with increasing of SF content in mortar, and correlated well with the rust area of steel rod measured after immersion corrosion tests. This shows that the electrochemical impedance measurement is the useful diagnosis method of corrosion of steel in concrete. The corrosion inhibition of steel rod in mortar by the SF addition was thought to be attributed to the consumption of dissolved oxygen by the corrosion of SF in mortar.
