氯离子侵蚀下钢筋在混凝土中腐蚀行为的EIS研究

应用电化学阻抗谱(EIS)研究环境介质中氯离子对混凝土中钢筋腐蚀行为的影响.结果表明,在测量的频率范围内,钢筋混凝土体系的阻抗谱图包含两个时间常数,分别对应于界面的双电层和钢筋表面的混凝土保护层.其低频段的半圆有些压扁,表明界面双电层的充放电行为偏离理想电容器,可归因于钢筋表面的不均一性.在浸泡后期,低频段出现拖尾,同时电荷转移电阻Rct减小了近两个数量级,这是由于钢筋表面的钝化膜已经破裂,发生活性腐蚀,况且氯离子浓度的增大加速了腐蚀发展过程.讨论了混凝土中在钢筋腐蚀发生,发展的过程中,其腐蚀电位Ecorr以及等效电路中的Rct和Warburg阻抗等元件的变化特征.

Corrosion Behavior of Reinforcing Steel in Concrete Subjected to Chloride Contamination By EIS

Electrochemical impedance spectroscopy(EIS) was employed to study the influence of chloride on the corrosion behavior of reinforcing steel in concrete.In Nyquist plot,the spectrum consists of two semicircles,indicating that the reinforced concrete system contained two time constants,one derived from electrical double layer of reinforcing steel and the other from the deposition film of concrete layer.The depressed semicircle in lower frequency featured the non_faradic behavior of the electrical double layer (EDL) deviated from idea capacitor due to diffusive effect which was attributed to the surface roughness of rebar and the inhomogenity of concrete layer.Then the EDL was denoted by a constant phase element (CPE) other than a capacitor in the equivalent circuit.At the late stage of immersion,a new element,Warburg resistance W evolved along with dramatic decrease in the value of polarization resistance,Rp,convincing the break down of the passive film and the initiation of active corrosion.The increase of Cl-] in external solution prominently accelerated this trend.