海水拌和混凝土中不锈钢筋早期腐蚀电化学行为研究

Electrochemical Behavior from Early Corrosion of Stainless Steel Bars in Seawater Mixed Concrete

目的研究海水拌和混凝土中不锈钢筋早期腐蚀电化学行为,从而有效解决海水海砂混凝土中的钢筋腐蚀问题。方法采用压滤法提取了海水拌和水泥浆体孔溶液,监测了孔溶液pH值和氯离子浓度随时间的变化,采用开路电位(OCP)、交流阻抗(EIS)等电化学方法,结合扫描电子显微镜SEM(EDS)、背散射(BSE)形貌观测手段研究了不锈钢筋腐蚀电化学行为,深入分析了不锈钢筋在海水拌合水泥浆体中的钝化动力学过程。结果尽管在早期304和316L不锈钢筋电位降至负值,均低于-0.35V,氯离子浓度达到0.7mol/L,但并未发生活化腐蚀,均可以发生正常钝化现象,海水拌和水泥浆体中316L不锈钢极化阻抗相比对照组(非海水拌合样品)有提升,腐蚀速率更低。随着水泥水化过程的发展,腐蚀电流密度逐渐降低至较低水平,304不锈钢腐蚀电流密度约为0.014μA/cm^(2),316L不锈钢电流密度低于0.006μA/cm^(2),展现出较高的耐腐蚀性能。海水拌和水泥浆体的电阻率与对照组浆体有一定差异,但整体相差较小。结论304和316L不锈钢尽管在早期可以发生正常钝化现象,电化学结果体现出较高的耐蚀性能,但其在服役期的氯离子临界浓度值及脱钝机理需要进一步研究。

With the shortage of freshwater and river sand resources,the application of seawater and sea sand concrete in marine structures has important practical significance.Seawater and sea sand concrete faces serious corrosion problems of steel bars.Previous studies have shown that using stainless steel bars can effectively solve the corrosion problem of steel bars in seawater and sea sand concrete.However,there is a lack of research on the passivation and depassivation mechanisms of stainless steel bars in seawater and sea sand concrete,and relevant theoretical results cannot support their application in practical engineering.The work aims to study the electrochemical behavior from early corrosion of stainless steel bars in seawater mixed concrete.The steel bars used were 304 stainless steel bars and 316L stainless steel bars with a diameter of 1 cm.Copper wires were welded at one end of the steel bars,and epoxy resin was used for sealing treatment.Sand paper was used to grind the steel bars step by step,and finally polished to a mirror surface to ensure a uniform surface state of the steel bars.The surface was cleaned with deionized water and ethanol,then blown to be dry with N_(2),and placed in a dryer for standby.A simulated solution was used to simulate the mixing of cement paste with seawater.The simulated seawater was deionized water composed of NaCl,MgCl_(2),Na_(2)SO_(4),CaCl_(2),KCl,and NaHCO_(3).In the experimental group,simulated seawater was used to mix cement paste(SW),while in the control group,deionized water was used to mix cement paste(DW),with a water cement ratio(w/c)of 0.4.The sample size of cement paste was 40 mm×40 mm×40 mm,and a protective layer thickness of 1 cm was used.Firstly,the pressure filtration method was used to extract the pore solution from the clean slurry samples at different ages.A pH meter was used to test the pH value of the pore solution at different times,and a Mettler Easyplus chloride ion potentiometric titrator was used to test the chloride ion concentration.The electrochemical behavior was monitored by the Swiss Vantone Autolab M 204 electrochemical workstation.The electrochemical impedance spectrum of the sample was tested regularly,with a sinusoidal disturbance amplitude of±10 mV and a frequency range of 100 kHz-10 mHz.Zsimpwin software was used to fit the AC impedance spectrum data and the corrosion rate of the reinforcement was calculated based on the fitting results.After the sample was split,the surface morphology and composition of the reinforcement were characterized by scanning electron microscopy(VEGA 3 TESCAN)combined with BSE and EDS.The results showed that although the potential of 304 and 316L stainless steel bars decreased to a relatively negative value at an extremely early stage,below-0.35 V,and the chloride ion concentration reached 0.7 mol/L,there was no biological corrosion,and normal passivation could occur.Compared with the control group,the polarization resistance of 316L stainless steel in seawater mixed cement paste was improved,and the corrosion rate was lower.With the development of cement hydration process,the corrosion current density gradually decreased to a lower level,and the corrosion current density of 304 stainless steel was about 0.014μA/cm^(2)and that of 316L stainless steel was below 0.006μA/cm^(2),exhibiting high corrosion resistance.The resistivity of cement paste mixed with seawater was somewhat different from that of the control group,but the overall difference was small.