Relationships between and cracking and corrosion of steel in concrete structure

实验1：采用电化学和电学方法，研究了覆盖层厚度、水灰比和浇筑方向对混凝土中钢筋大细胞腐蚀的影响。嵌入1% Cl -污染混凝土中的钢（阳极）与嵌入Cl -污染混凝土中的不锈钢板（阴极）电连接。在3.27% NaCl溶液中湿润1天，在自然环境中干燥1天。结果表明：1)阳极钢的覆盖厚度对Cl^-污染混凝土中钢阳极的宏细胞腐蚀程度有影响；2)水灰比对腐蚀有显著影响；3)水平浇筑混凝土中钢的腐蚀明显高于垂直浇筑混凝土，这是由于混凝土的渗水。试验2：采用钢筋混凝土梁试件进行加速腐蚀试验，研究了覆盖层厚度、裂缝、水灰比和浇筑方向对混凝土中钢筋大细胞腐蚀的影响。为了测量大细胞腐蚀电流，钢筋被涂上环氧树脂膜，只在中心留下27毫米的区域（阳极）未受保护。钢被电连接到不锈钢棒（阴极）设置在钢附近（图1）。将梁试件加载到规定宽度的裂缝中，并在65‰/ 3.2% NaCl溶液中进行1天的润湿和1天的室内干燥，重复试验35次。并对其电化学特性和腐蚀性能进行了测试。结果表明：1)电化学特性与腐蚀电流的变化一致，可以无损地判断混凝土中钢筋的腐蚀状况。极化电阻的积分倒数与腐蚀程度有关。2)覆盖层厚度越大，裂纹宽度越窄，腐蚀程度越低。3)低水灰比混凝土显著抑制腐蚀。在w/c为60%的混凝土中，覆盖层对腐蚀的影响较大，在w/c为40%的混凝土中，裂缝的影响较大。4)混凝土浇筑方向对钢的腐蚀没有影响。少

Experiment 1: The effects of cover thickness, water cement ratio and casting direction on macrocell corrosion of steel in concrete was investigated by electrochemical and electrical methods. Steel (anode) embedded in 1% Cl^- contaminated concrete was electrically connected to stainless steel plate (cathod) embedded in Cl^- contaminated concrete. The specimens were subjected to repeated cycles of one day wetting in 3.27 %NaCl solution and one day drying in natural environment.It was found that : 1) cover thickness over anode steel has effects on the macrocell corrosion degree of steel anode in Cl^- contaminated concrete, 2) water cement ratio considerably influenced corrosion, 3) corrosion of steel in concrete cast horizontally was remarkably higher than that in concrete cast vertically due to bleeding of concrete.Experiment 2: The effects of cover thickness, cracking, water cement ratio and casting direction on macrocell corrosion of steel in concrete was investigated by a accelerated … More corrosion test using reinforced concrete beam specimens. In order tomeasure macrocell corrosion currents, reinforcing steels were coated with epoxy resin films, leaving only 27 mm zone (anode) in the center unprotected. The steel was connected electrically to stainless bars (cathod) set near the steel (Fig.1). Beam specimens were loaded to introduce cracks of defined width and subjected to 35 repeated cycles of one day wetting in 65 ﾟC, 3.2 % NaCl solution and one day drying under room environment. The electrochemical characteristics and corrosion deteriora lion were also measured. It was found that : 1) The electrochemical characteristics coincided with change of corrosion currents, and it is possible to judge undestructively the condition of corrosionof steel in concrete. The integration of the reciprocal of polarization resistance related to the degree of corrosion.2) As cover thickness was large and crack width was narrow, the degree of corrosion decrease.3) Low water cement ratio concrete inhibited remarkably corrosion. Effects of cover on corrosion was large in w/c 60 % concrete and effects of crack was large in w/c 40 % concrete.4) The casting direction of concrete had not effect on corrosion of steel. Less