【作者】 乔国富；

【导师】 欧进萍； Farhad Ansari；

【作者基本信息】 哈尔滨工业大学 ， 工程力学， 2008， 博士

【摘要】 本文对氯离子环境下混凝土中钢筋腐蚀的监测问题进行了研究,应用电化学方法揭示了混凝土中钢筋腐蚀的机理,给出了适合腐蚀监测实际工程应用方法,研制开发了五电极和全固态束流式两种腐蚀传感器,搭建了腐蚀监测系统,并在混凝土梁中进行了钢筋腐蚀监测实验。研究结果表明,所进行的一系列研究为实现钢筋腐蚀监/检测开辟了新的途径。首先,采用电化学阻抗谱(Electrochemical Impedance Spectrum, EIS)技术分别对不同温度、不同浓度NaCl溶液中内置Q235碳钢样品的混凝土试件的阻抗特性进行了研究。研究结果表明混凝土中钢筋腐蚀的EIS特性体现为三个方面:1)在Nyquist图的高频及中频段出现两段容抗弧。这说明除了钢筋/混凝土界面处体现的容抗特性以外,混凝土本身也存在一定的容抗特性。2)中频段的容抗弧发生一定程度压扁。这说明出现了体现弥散效应的常相位角元件(Constant Phase Element, CPE)项,弥散效应的产生是由于混凝土中钢筋/砂浆界面的粗糙性、孤立的反应区域以及混凝土本身异质特性决定的。3)低频段发生拖尾现象,说明腐蚀体系出现了Warburg阻抗。进一步分析发现低频段Nyquist图偏离了Warburg阻抗应体现的45°线,出现这一现象的原因有二:其一,钢筋/混凝土之间的粗糙界面导致扩散过程在一定程度上体现为球形电极扩散;其二,蚀点的存在使得Nyquist曲线在低频段呈现一定容抗特性。其次,基于电化学噪声(Electrochemical Noise,EN)技术,研究了0%及3.5%NaCl溶液中混凝土内钢筋点蚀特性。研究结果表明钝化态钢筋的EN信号体现为高频白噪声;而Cl-引起点蚀的电位噪声(Electrochemical Potential Noise,EPN)中存在较大的漂移,EPN及电流噪声(Electrochemical Current Noise,ECN)中出现了明显的暂态峰,两者都体现为暂态下降(升高)、缓慢恢复的特征。通过功率谱(Power Spectral Density,PSD)分析可知,EPN及ECN的PSD曲线中出现了典型的三段式分布。极限谱噪声阻Rf→0与EIS的研究结果比较可知,在信号趋势去除后Rf→0与EIS测得的阻抗模Z具有很好的一致性。考虑到工程中点腐蚀监测EN信号中存在较大的趋势,采用对时变系统分析具有诸多优点的Sym4小波对EN进行了分析,分析结果表明采用小波分析EN得到的信号能量分布曲线(Energy Distribution Plot,EDP)能够判断点蚀的发生,较PSD等对时变系统信号处理更具优势。第三,推导了混合电位控制下电极反应方程式,并分别对稳态及暂态的工程应用简化方法进行了研究。讨论了扩散作用及CPE项对暂态测量结果的影响。验证了时间常数比半电位法具有更大的优越性,在氧气匮乏湿度较大的环境下,能够准确判断钢筋的腐蚀状态。对不同浓度的NaCl溶液中内置Q235碳钢样品的砂浆试件在恒电流及恒电位激励下的充放电过程进行了测试,并对充电过程试验结果采用分段解析的方法进行了分析,验证了工程简化方法的准确性。第四,首先制备了腐蚀传感器的核心部件-全固态参比电极,并对所制备的参比电极进行了性能检测。检测结果表明所制备的参比电极长时电位稳定,不易受到混凝土内各种离子的干扰,具有良好的抗极化特性,温度响应系数为-0.48mv/℃～-5.2 mv/℃。其次,应用所制备的全固态参比电极研制、开发了五电极及全固态束流式腐蚀传感器,其中五电极腐蚀传感器能够进行常规电化学方法及EN测试;通过电场的有限元分析可知,全固态束流式腐蚀传感器能够较好地约束辅助电极的电力线分布,从而较准确地确定工作电极的面积,进而准确测定钢筋腐蚀速率。第五,应用所开发的传感器平台及工程测试方法对加速腐蚀后的钢筋混凝土梁的腐蚀状态进行了监测,并研究了不同腐蚀状态下梁基本力学性能的退化。监测的结果表明加速腐蚀完成后的混凝土内钢筋腐蚀的腐蚀电流密度icorr的量级为10+1μA/cm2,而钝化态梁内钢筋的腐蚀速率仅为10-1μA/cm2。EN的监测结果表明钢筋表面发生了严重的点蚀。梁的正截面承载力试验发现钢筋从未腐蚀到严重腐蚀过程中,梁的破坏形态从典型的适筋梁破坏逐渐转化成典型的少筋梁破坏。随着腐蚀程度的增加,梁的极限承载力下降、延性降低、刚度减小。更多还原

【Abstract】 Corrosion monitoring of reinforcing steel in concrete with chloride iron environment has been studied in this paper. Electrochemcial methods have been used to explore the corrosion mechanics. Some corrosion monitoring methods for practical engineering have been discussed.Also, five-electrode corrosion sensor and all solid state-current confined corrosion snesor has been developed and the corrosion monitoring system has been setup. The corrosion monitoring system has been practiced in the RC beams. The results show that the research in the paper has explored a new way to realize the corrosion monitoring and detecting.The main works of this paper are as follows:1. The impedance character of the specimens of Q235 carbon steel embedded in cement mortar at different temperature and in different concentration of NaCl solution have been studied by electrochemical impdedance spectrum technique (EIS).The results show that the impedance charater of the specimen includes three aspects.1) There are two parts of capacitive arcs at the high frequencies and medium frequencies of the Nyquist diagram. This shows that the concrete has some capacitive character besides the interface between the steel bar and the concrete.2) The capcitive arc at the medium frequencies has been flattened in some degree.This phenomen is cuased by the constant phase element (CPE).CPE is also named dispersion effect.The coarse interface of the steel/concrete, isolated reaction region and the heterogeneous nature of concrete are the most important factors causing the dispersion effect.3) The phenomen of smearing effect has appeared at low frequencies.The Warburg impedance which is used to explain the diffusion effect can cause the smearning phenomen. But the plots in the Nyqusit diagram are deviated from the line with the coeff. of 1. There are two kinds of factors which can cause such phenomen. Firstly, the diffusion process from the concrete to the carbon steel can be treated as spheric electrode diffusion in some degree for the coarse surface of the specimen.Secondly, the corrosion pit causes that the character of the Nyqusit plots at low frequencies embodies some capacitive character.2. The electrochemical noise (EN) technique has been applied to study the pitting character of the carbon steel embedded in cement mortar. The concentration of the NaCl solution used to immersed the cement specimen are 0% and 3.5%, respectively.The results show that the EN of the passivated steel is white nosie. There is a large trend in the EPN when the specimen is immersed in 3.5%NaCl solution. The apparent transient peaks have appeared in EPN and ECN. Decreasing (or increasing) suddenly and recovery slowly is the typical shape of the transient peak. The typical three-segment plots have apperared in the PSD diagrams of EN.When the EN is detrended, the Rf→0 calculated by PSD is equal approximatly to the impedance Z measured by EIS.Concering the larger amplitude of the trend in EN in practical engineering, Sym4 wavelet has been used to analyze the EN. The results show that the energy distribution plot (EDP) can be used to confirm the occurrence of the corrosion pit.The EDP method is more effectively than PSD to treat time variance system.3. The reaction equation of the electrode which is controlled by mixed potential theory has been deduced and the simplified methods which adapt to practical engineering in steady state and transient state measurement have been studied.The influence of diffusion and CPE effects to the results by transitent measurement have been discussed. As the extition of the system is a current step, the time constant of the potential response is a more effective parameter to identify the corrosion status of the steel than that of the half-potential method.The time constant can identify the corrosion status correctly when the oxygen is rare or the humidity is very high in the concrete. Many specimens have been used in the experiments to certify the reability of the simplified methods.The data during the charging process has been analyzed by segmented method.4. A novel all solid state reference electrodes have been prepared and the performance of the reference electrode is studied. The reference electrode is immune to the irons in the concrete and the long time stability is perfect. Also, the anti-polarizetion character of the reference electrode is perfect. The coefficient of temperature response is from -0.48mv/℃to -5.2 mv/℃. Secondly, applying the all solid state reference electrode, the five-electrode corrosion sensor and all solid state-current confined corrosion sensor have been developed. The general electrochemical measurements and EN measurement can be realized on five-electrode corrosion sensor.According to the analysis results of the finite element method, the area of the working electrode(WE) can be identified exactly by the all solid state-current confined corrosion sensor, so the corrosion rate of the steel bar can be measured accurately by the corrosion sensor.5. The developed corrosion sensors have been used to monitor the corrison statues of the concrete beam.The basical mechanical property of the corroded beam has also been studied. After the accelerated corrosion, the corrosion current degree of the steel bar is almost 10+1μA/cm2.But the current of the steel bar in fresh concrete is 10-1μA/cm2.According to the change of the EDP, we can see that the pitting corrosion has occurred on the steel surface.By the experinments of the cross-section bearing capacity of the beams, we can find that the failure mode of the beams change from tipical adequacy beam to the insufficient beam.As the corrosion degree increases, the ulitimate bearing capacity, the ductility and the stiffness of the beams decrease gradually.更多还原