The question of how adding steel fiber (SF) to concrete would affect the corrosion behavior of steel reinforcing bars was studied by immersion tests in a 3 mass percent NaCl solution for 363 days. The tests were conducted on steel bar/mortar specimens with different SF content (0-2 vol percent). Each specimen's corrosion potential and electrochemical impedance were measured during the testing. Corrosion potential was not much affected by changes in the SF content. Electrochemical impedance measured at corrosion potentials was analyzed to get the charge-transfer resistance (R_(ct)) using an equivalent electrical circuit with the R_(ct), Warburg impedance, and a constant-phase element. The corrosion rate of steel bars in mortar estimated from the reciprocal of the R_(ct) decreased inversely to the SF content of the mortar, and correlated well with the rust area of the steel bars measure after the immersion tests. This shows that electrochemical impedance measurement is a useful method for diagnosing corrosion of steel in concrete. The inhibition of corrosion of the steel bars resulting from the SF addition was attributed to the consumption of dissolved oxygen by the corrosion of SF in the mortar.
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