碳化条件下混凝土中钢筋腐蚀pH阈值研究

目的 确定碳化条件下几种典型缓冲溶液及模拟混凝土孔隙液中钢筋的腐蚀pH阈值范围。方法 采用电化学阻抗谱法，对不同pH、不同配制方法的缓冲溶液及模拟混凝土孔隙液中的钢筋试片进行电化学测量，选用不同的等效电路进行拟合，对测量中钢筋试片发生的电化学过程进行简要阐述。结合阻抗谱测量结果、等效电路拟合结果及工作电极典型宏观形貌，判断钢筋试片腐蚀状态，给出不同溶液对应的钢筋腐蚀pH阈值范围。结果离子环境不同，各缓冲溶液及模拟混凝土孔隙液中钢筋腐蚀pH阈值均存在一定差异，位于9～10.5不等。结论 混凝土碳化引入的HCO₃~–和CO₃^2–对钢筋腐蚀有促进作用。混凝土孔隙液pH越低，钢筋腐蚀越容易发生。因此，仅根据pH判断混凝土中钢筋腐蚀状态的方法并不可靠。

Study on pH Threshold of Rebar Corrosion in Concrete under Carbonation Condition

The work aims to study pH thresholds of rebar corrosion of different types of buffer solution and simulated concrete pore solution under carbonation. The electrochemical impedance spectroscopy was used for electrochemical behavior measurement of rebar specimens in buffer solution and simulated concrete pore solution of different pH and preparation methods. Different equivalent circuits were selected for fitting, so as to explain the electrochemical process of steel specimen during measurement, while the measurement and simulation results were used to judge the corrosion condition of specimens in combination with the typical macro morphology of working electrodes, through which the pH thresholds of rebar corrosion corresponding to different solution were given. The result showed that due to the different ionic environment, the pH threshold of rebar corrosion in each buffer solution and simulated concrete pore solution was different, ranging from 9 to 10.5. In conclusion, the introduction of HCO3– and CO32– promotes the corrosion of rebar in concrete and the rebar corrosion is more likely to initiate with lower pH. The reliability of judgement on corrosion condition of rebar in concrete based on pH values is limited.