海洋环境下混凝土中钢筋加速锈蚀研究

为研究海洋环境下氯离子渗透导致混凝土中钢筋电化学腐蚀行为、锈胀裂缝发展及锈斑分布情况，同时为青岛地铁高性能混凝土配合比的优化及耐久性能提供试验依据，设计了上置腐蚀溶液槽的钢筋混凝土试件，并针对C40、C50、C50S和C55 4类钢筋混凝土试件开展恒电位加速试验。试验结果表明： 采用本试验方法加速钢筋混凝土锈蚀，靠近混凝土保护层一侧的钢筋锈蚀严重，钢筋出现点蚀现象，与自然环境下钢筋锈蚀情况一致； 依据交流阻抗谱图拟合的钢筋电荷转移电阻随腐蚀时间增加而下降，依据计算的腐蚀电流密度，测试的钢筋电流演变拐点可确定C40、C50、C50S和C55混凝土中钢筋脱钝时间分别为60～70、80～90、90～100、100～110 h，钢筋混凝土锈胀开裂时间分别为120、136、176、264 h； 采用图像处理软件依据灰度值不同可实现锈斑分布的定量计算，混凝土护筋能力排序为C55>C50S>C50>C40。

Corrosion Behavior of Reinforced Bar in Concrete in Marine Environment

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.