Abstract:

In order to study the electrochemical corrosion behavior of reinforce bar induced by permeation of chloride ions in marine environment, the corrosion crack propagation and rust distribution, and provide experimental basis for the mixing proportion optimization and durability of the high performance concrete used in Qingdao Metro, four types of reinforced concrete specimens, C40, C50, C50S and C55, with corrosion solution tank are designed and tested by constant potential acceleration. The experimental results show that: (1)The upper surface of reinforced bar close to the concrete cover is corroded, and the spot corrosion of reinforced bar can be observed, which is in accordance with the reinforced bar corrosion in natural environment. (2)The charge transfer resistance of reinforced bar fitted according to Nyquist diagram tends to decrease with corrosion time; according to the evolution of calculated corrosion current density and electricity, the unpassivation time and cracking time of concretes can be determined, and the unpassivation time of C40, C50, C50S and C55 concrete are 60-70 h, 80-90 h, 90-100 h and 100-110 h, respectively; and the cracking time of C40, C50, C50S and C55 concrete are 120 h, 136 h, 176 h and 264 h respectively. The quantitative calculation of rust distribution can be completed by image processing software based on the gray level difference. The protection ability of the C55 concrete to reinforced bar is the highest, followed by those of C50S and C50, and that of C40 is the lowest.

Key words: marine environment, reinforced bar corrosion, constant potential acceleration test, electrochemical impedance spectroscopy, corrosion crack