干湿循环作用下混凝土中氯离子传输性能及临界浓度研究

发布时间：2018-09-11 16:51

【摘要】：海洋环境中浪溅区与潮汐区是钢筋混凝土结构耐久性破坏最为严重的两个区域，由此导致的钢筋混凝土结构耐久性失效问题给整个社会带来诸多安全隐患和巨额经济损失。因此，正确认识其腐蚀行为成为耐久性研究的重要课题之一。本文根据浪溅区与潮汐区钢筋混凝土结构的腐蚀机理，，研究了干湿循环作用下混凝土中氯离子的传输规律，探讨了混凝土中钢筋腐蚀临界点的监测与判断方法，分析了混凝土中钢筋腐蚀的临界氯离子浓度，最后对钢筋混凝土结构耐久性寿命进行预测分析。研究成果将为海洋腐蚀环境中钢筋混凝土结构的钢筋锈蚀诊断及耐久性寿命预测提供理论依据。具体内容如下：论文采用化学滴定法和氯离子选择电极法对标准浓度NaCl溶液进行对比测试试验，结果表明了氯离子选择电极法比化学滴定法的测试精度高；综合利用交流阻抗谱法、线性极化法和Tafel极化法对混凝土中钢筋开始腐蚀临界点进行了监测试验，测试结果及拟合分析表明此方法可以对混凝土中钢筋腐蚀的临界时间点进行有效监测。开展了不同干湿循环时间比例对混凝土中氯离子传输性能影响的试验研究，结果表明：不同干湿循环时间比例作用下对流区深度均在2mm左右；对流区深度Δx处的氯离子浓度值Cs,Δx与干燥时间存在线性关系，随干燥时间的增加而降低，但降低幅度较小；氯离子扩散系数与干湿时间比值之间存在明显线性相关性，随干湿时间比值的增加而增大。通过交流阻抗谱法等钢筋锈蚀检测技术研究了钢筋腐蚀的临界氯离子浓度，分析了干湿循环时间比例、循环周期、粉煤灰掺量对临界氯离子浓度的影响。试验结果表明：临界氯离子浓度与试件干燥过程结束时饱和度之间有明显的线性相关性，随着试件干燥过程结束时饱和度的增大而减少；临界氯离子浓度值随着干湿循环周期的增大，基本呈增大趋势；临界氯离子浓度随粉煤灰掺量的增加先增大后减少，说明粉煤灰虽然可以增加混凝土的密实性，但也降低混凝土孔溶液的pH值，因此其抗氯离子侵蚀能力随着粉煤灰掺量的增加先增强后下降。在上述研究基础上，对干湿循环作用混凝土结构的耐久性寿命进行了预测，结果表明此区域混凝土结构的使用年限一般为10~20年，远达不到设计要求，因此应采取必要的耐久性设计及防护措施。
[Abstract]:In the marine environment, the wave splash area and the tidal zone are the two regions where the durability of reinforced concrete structures is most seriously damaged. The durability failure of reinforced concrete structures has brought a lot of safety risks and huge economic losses to the whole society. Therefore, the correct understanding of its corrosion behavior has become an important subject of durability research. According to the corrosion mechanism of reinforced concrete structures in the splash zone and tidal zone, this paper studies the law of chloride transfer in concrete under the action of dry-wet cycle, and discusses the monitoring and judging method of the critical point of reinforcement corrosion in concrete. The critical chloride concentration of reinforced concrete corrosion is analyzed. Finally, the durability life of reinforced concrete structure is predicted and analyzed. The research results will provide theoretical basis for corrosion diagnosis and durability life prediction of reinforced concrete structures in marine corrosion environment. The main contents are as follows: chemical titration method and chloride ion selective electrode method are used to test the standard concentration of NaCl solution. The results show that the chloride ion selective electrode method is more accurate than the chemical titration method. Based on AC impedance spectrum method, linear polarization method and Tafel polarization method, the critical corrosion point of steel bars in concrete is monitored and tested. The test results and fitting analysis show that this method can effectively monitor the critical time point of steel bar corrosion in concrete. The effect of different dry and wet cycle time ratio on chloride transport performance in concrete was studied. The results showed that the depth of convective zone was about 2mm under different dry and wet cycle time ratio. The chloride concentration value Cs, 螖 x at the depth of convection zone 螖 x has a linear relationship with the drying time and decreases with the increase of drying time, but the decrease is small, and there is a significant linear correlation between the chloride diffusion coefficient and the ratio of dry and wet time. With the increase of the ratio of dry and wet time, it increases. The critical chloride ion concentration of steel bar corrosion was studied by means of AC impedance spectroscopy and other techniques. The effects of dry and wet cycle time ratio cycle period and fly ash content on critical chlorine ion concentration were analyzed. The experimental results show that there is a significant linear correlation between the critical chlorine concentration and the saturation at the end of the drying process, which decreases with the increase of the saturation at the end of the drying process. With the increase of dry and wet cycle, the critical chlorine ion concentration increases first and then decreases with the increase of fly ash content, which indicates that fly ash can increase the compactness of concrete. However, the pH value of concrete pore solution is also reduced, so its resistance to chloride ion corrosion increases first and then decreases with the increase of fly ash content. On the basis of the above research, the durability life of concrete structures subjected to dry-wet cycling is predicted. The results show that the service life of concrete structures in this area is generally 10 ~ 20 years, which is far from the design requirements. Therefore, the necessary durability design and protective measures should be taken.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU528

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