A survey on the macro-cell corrosion in structures and a study on its mechanism

为了阐明宏细胞腐蚀对结构的影响，对(1)结构的损伤情况、(2)地下结构的宏细胞、(3)钢筋混凝土结构的宏细胞进行了调查。同时，还分析了大型钢筋混凝土结构和组合结构中存在严重的宏电池腐蚀的可能性。比较宏蜂窝和微蜂窝的影响，在结构轴向几乎不可能出现严重的宏蜂窝。对于项目(3)，试验研究了裂缝、接缝、修补方法和外加剂对混凝土的影响。结果表明：(1)无裂纹时，高炉矿渣粉和硅灰微粉的抗腐蚀效果较好，但有裂纹时，防腐效果减弱，尤其是轴向定向裂纹，且裂纹处的加固部位趋于阳极化。(2)接缝和裂纹引起宏电池腐蚀，暴露在其上的钢筋区域通常是阳极的，但有时也可以是阴极的。(3)修复区趋于阴极，修复区与未修复区的连接处为阳极，腐蚀速度较快。

To clarify the influence of the macro-cell corrosion in structures, investigations on (1) conditions of damaged structures, (2) macro-cell in underground structures, and (3) macro-cell in RC structures, were done.For item (1), the damages in steel structures at port, RC structures and composite structures were surveyed. Also, the possibility of severe macro-cell corrosion in massive RC structures and composite structures were shown.For item (2), experiments about the macro-cell in long underground structures were done. Comparing the influence of macro-cell and that of micro-cell, there was almost no possibility of severe macro-cell in the axial direction of structures.For item (3), the influences of cracks, joints, repair methods and admixtures for concrete were experimentally studied. The results show, (1) Without crack, blast furnace slag powder and silicafume powder were effective against corrosion, however, with cracks, the effects reduced especially with axially directed crack, also the areas of reinforcement exposed to cracks tended to be anodes. (2) Joints and cracks caused macro-cell corrosion and the areas of reinforcement exposed to them were usually to be anodic, however, sometimes they can be cathodic. (3) The repaired areas tended to be cathodic and the joints between repaired and unrepaired part could be anodes and the corrosion rate could be very fast.