Relationship between chloride ion concentration and pH on depassivation of steel rebar embedded in concrete was investigated by a two frequencies impedance measurement using probe electrodes. A saturated calcium hydroxide solution was used for the electrolyte solution as simulated concrete pore solution. The pair of probe electrodes, which simulates the steel rebar, was immersed in the electrolyte solution prepared by arbitrary concentration of chloride ions, and the two frequencies impedance measurement was performed. Air was supplied to the electrolyte solution in order to simulate the neutralization of concrete during the measurement. The charge transfer resistance related to electrode/solution interface, R_ct, were estimated from the two frequencies impedance measurement of probe electrodes in each electrolyte solution, demonstrating that the R_ct was drastically decreased with decreasing the pH of electrolyte solution, namely, the depassivation on steel rebar. The corrosion conditions of steel rebar were categorized as “passive state”, “depassivation”, and “corrosion” based on the changes of monitoring of R_ct and pH in each electrolyte solution, and these results were plotted on the two dimensional diagram composed of chloride ion concentration and pH of electrolyte solution. The conditions for depassivation of passive film on steel rebar were discussed.

The authors participated in a project “Technical collaboration project on seawater utilization for concrete structure of petroleum facilities as construction and maintenance management, Kuwait” that Japan Society of Corrosion Engineering （JSCE） received from Japan Cooperation Center Petroleum （JCCP）, and supported research in Kuwait. In this paper, the results of the study on concrete mixed with seawater performed as part of the above project are reported.

In the present paper, cationic precipitation inhibitors effective for Fe corrosion in aerated 0.5 M Na₂SO₄ are discussed based on the hard and soft acids and bases （HSAB） principle. Multivalent metallic cations are readily precipitated by the formation of their hydroxides due to stable hard acid and hard base interaction. They suppress the cathodic process of Fe corrosion, reduction of dissolved oxygen but promote the anodic process of Fe dissolution. High inhibition efficiencies are obtained by the addition of anionic precipitation inhibitors suppressing the anodic process. On the other hand, high concentration of cerium （III） ion, Ce^3＋ inhibits both cathodic and anodic processes by the direct formation of oxide layer with evolution of H₂.

In order to understand the flying characteristics of the amount of salinity derived from sea, a wide-area airborne salt survey in Shimane was conducted during the same period. The resulting data is a valuable materials in predicting the spatial distribution of airborne salt level. We discuss the relationship between the measured values of airborne salt level and the predicted values proposed by the authors by use of meteorological observation data. It was confirmed that the prediction of the airborne salt level from the meteorological observation data was possible with considerable accuracy.

Many facilities were built underground to maintain communication, and they have been feared that corrosion of the inner surface of a steel pipe may cause failure in cable laying or reduct the seismic performance. To obtain long-term corrosion rate, a specimen made of steel pipe was placed in a manhole that is assumed to be close to the actual environment, and the corrosion rate was measured by inspecting the weight loss over four years. In addition to this, the specimen are observed with SEM and analyzed with XPS. There are some dense layers on specimen consist of FeOOH, Fe₃O₄, Fe（OH）₂CO₃. Because of dense layer, corrosion rate can be proportional to 1/2 power of time. The coefficients of the model equation were determined from the measured values.