The Study of Chloride Ion Migration in Reinforced Concrete Under Cathodic Protection

00778844424703251999PDFTech ReportFHWA-OR-RD-00-03SPR 357Ion exchangeCathodic protectionReinforced concreteIon migrationZinc anodeCathodesUnited StatesOregonUnited States. Federal Highway AdministrationOrlova, Nadejda V.Westall, John C.Rehani, ManuKoretsky, Milo D.Oregon. Dept. of TransportationUnited States. Federal Highway AdministrationUS Transportation CollectionThe migration of chloride ions in concrete with steel reinforcement was investigated. Mortar blocks (15 cm x 15 cm x 17 cm) of various composition (water to cement ratio, chloride ion content) were cast with an iron mesh cathode imbedded along one face and a thermally sprayed zinc anode applied to the opposite face. Current densities of 0.033 and 0.066 A / m2 were applied to the blocks over a period of one year at constant temperature and humidity. The zinc face was covered with a pond of saturated calcium hydroxide to prevent polarization of the zinc concrete interface. Over the course of polarization, potential vs. time curves were recorded and samples of mortar were extracted for determination of chloride concentration. An ion chromatography method was developed for the analysis of small samples of mortar for chloride. The method allowed for the measurement of chloride concentration in mortar samples with a long term overall relative standard deviation of 3.2% in the concentration range 1-15 mg/L in the water extract of the mortar. Under the conditions of the study, no significant migration of chloride ions could be detected over the one-year test. This result was consistent with that which would be expected with a simple transport model of the system. Random fluctuations that wereobserved in the chloride concentration profiles were attributed to the inhomogeneous pore structure of the mortar on the scale of the sample size and the associated inhomogeneity in the chloride distribution. Future studies of these phenomena should be designed with larger blocks and larger samples of mortar for chloride analyses; (ii) an automatic misting device to obviate the need for the calcium hydroxide solution; and (iii) higher current densities, longer periods of polarization, or both.85