A Study of Depassivation of Steel in Concrete

摘要

Corrosion failure of steel embedded in concrete is an important design consideration in reinforced or prestressed concrete structures. This study was made on passivation and depassivation of steel in a simulated concrete environment under the controlling influence of the chloride ion. Tests of mechanisms related to passivation were performed to determine whether: (1) passivated steel maintains passivity when exposed to a nonpassivating environment, (2) chloride ions accelerate depassivation of steel, or (3) film formation is retarded by the presence of chloride. Tests used aqueous solutions, but comparisons with cement-water slurry and saturated calcium hydroxide solutions were also performed. Depassivation of steel occurs quickly after removing the passivating environment. Chloride accelerates film breakdown in a passivated specimen and aids in establishing active corrosion cells in unpassivated specimens. The presence of 0.08M chloride in normally passivating solutions of saturated calcium hydroxide is sufficient to prevent passivation of steel. Corrosion can occur (subject to local conditions) at chloride concentrations as low as 0.02M. (Author)