Metallurgical Effects on Chloride Ion Corrosion Threshold of Steel in Concrete

摘要

The chloride-induced corrosion of reinforcing steel bars (rebar) in concreteseriously limits durability of reinforcing concrete structures. This investigation examines key issues in pitting corrosion and chloride corrosion threshold of rebar in alkaline solutions ((CI(sup -))(sub T). The effect of rebar surface condition on (CI(sup -))(sub T) values was evaluated using the open-circuit immersion method (OCI). Results indicate that sandblasted rebar had higher (CI(sup -))(sub T) values than as-received or prerusted rabar. The threshold chloride-to-hydroxide ratio (CR(sub T)) increased with pH, suggesting that the intrinsic inhibiting effect of hydroxide ions was stronger at higher (OH(sup -)) levels. Ranges of total chloride threshold in concrete (C(sub T)(sub T)) were estimated based on (CI(sup -))(sub T) from liquid solution measurements and on available chloride binding data, and were found to be consistent with values observed in practice. The effect of several important factors ((CI(sup -)), pH, rebar surface finish, polarization scan rate, passive film maturity, specimen size) on pitting (E(sub p)) and repassivation (E(sub r)) potentials in alkaline solutions (pH1.16 to 13.6) was investigated with the cyclic polarization technique (CYP). It was found that E(sub p) was not a unique function of the test condition and that is variability tended to increase with decreasing chloride-to-hydroxide ratio.