滨海盐雾区复杂环境下混凝土表层微环境的特征及对多重离子在表层传输过程的影响研究

Plenty of concrete structures located in the coastal salt-spray area are suffering from durability problems, due to the various corrosive substances and complex environmental factors in such a special environment. So far, researches related to concrete durability in coastal salt-spray area mainly focus on transport processes and mechanisms in interior concrete, studies on the surface-layer of concrete as the initial and boundary conditions of transport processes can be rarely found in the literature. In the proposed project, monitoring sites are planned to be built up in coastal zone to collect data and establish the database of environmental factors in coastal salt-spray area. Based on the database, a laboratory for the simulation of coastal salt-spray environment is planned to be designed and built up, in which environmental factors will be comprehensively considered and accelerated experiments can be carried out. Through the comparison of accelerated experiments and real tests on concrete structures under service, the extent of the surface-layer micro-environment of concrete in salt-spray area will be defined, the characteristics of the micro-environment, including the gradient of environmental factors and the influence of the surface-layer micro-environment on the external environment, will be investigated, and the exchange of moisture and ions between the surface-layer and external environment driven by the gradient of environmental factors will be quantified. In combination with the environmental factors, the proposed project also aims to clarify the initial and boundary conditions of the transport of multiple ions in concrete, and to model the deposit and transport of multi-ions in the surface-layer of concrete. The interactions between the multiple ions and cement hydrates and their influences on the microstructure of cement paste and transport properties of concrete will also be studied using techniques such as SEM, XRD, MIP, etc., so that the transport process of multiple ions under such complex environment can be explained at micro-scale. Results of the proposed project will be of great academic and practical significance in structural design, service life prediction and durability assessment of concrete structures in coastal salt-spray area.

滨海盐雾区腐蚀源多，环境因素复杂，大量处于该区域的结构出现了耐久性问题。相关研究主要集中于混凝土内部的传输过程，较少关注作为传输初始条件和边界条件的表层。本课题拟在滨海盐雾区进行现场观测，形成系统的环境数据库，设计滨海盐雾区综合模拟试验室；通过加速试验和实际结构的对比分析，定义盐雾区混凝土表层微环境的影响范围，研究盐雾区表层微环境的特性，包括微环境与外界环境间的环境梯度，及对外界环境的响应规律和机理等，量化表达环境梯度驱动对表层与环境间水分和离子的交换作用；明确多离子传输的初始和边界条件，研究多重离子在表层的沉积和传输过程，建立数学模型；通过SEM、XRD和MIP等设备，分析不同离子与水泥凝胶体反应后带来的微观结构变化及对表层传输性能的影响，对多因素复合作用下离子的传输过程作出微观解释。本课题的研究成果将在滨海盐雾区混凝土工程的结构设计、寿命预测和耐久性评估中产生广泛的学术和工程应用价值。

滨海盐雾区存在二氧化碳、氯离子等腐蚀介子，大量处于该区域的结构出现了耐久性问题，相关的研究较少关注作为传输初始和边界条件的表层。本课题通过在盐雾区现场观测，形成了比较完整的盐雾区环境参数，研究了盐雾区表层微环境的特性，分析了多重离子在混凝土表层的传输过程，在对滨海盐雾区已建混凝土结构进行耐久性评估、寿命预测和对新建结构进行耐久性设计时，具有重要的现实意义和学术价值。主要研究内容、重要结论及关键数据包括：深圳测定滨海盐雾区域，全年温度的变化区间为15℃至38℃，1、2、3、4、5、11和12月份温度较低，7、8和9月份温度较高；高湿度区间集中出现在夏季和秋季，全年湿度的变化区间为50％至80％；1和12月份中大气氯离子含量最高， 6月份最低；离海岸线距离对氯离子浓度影响大，海岸线附近氯离子浓度为1.650 mg/m³，较远时为0.420 mg/m³，随着距离增加，氯离子浓度迅速降低；盐雾区二氧化碳的含量在1到3月份较高，之后不断下降到9月份，全年二氧化碳含量高的时间在春冬季；混凝土表层微环境相对于外界环境变化存在时间滞后效应，混凝土在干燥和湿润过程中，湿度扩散系数变化规律不一致，干燥时的湿度扩散系数要明显低于湿润过程；混凝土表层微环境湿度高于外界环境时，内部微环变化过程中，表层氯离子浓度有一定的上升，低于外界时，表层氯离子浓度有所下降，但内部微环变化过程对结合氯离子的影响不大；当碳化和盐雾周期均为28 d时，碳化对盐雾氯离子在混凝土中传输的作用随深度而改变，存在一个转折点，深度小于该点时，碳化使自由氯离子浓度降低，超过这个深度后，碳化使自由氯离子浓度提高；碳化降低了混凝土中盐雾氯离子的结合能力，会导致混凝土氯离子有效扩散系数增大，在先盐雾后碳化的试验中，最高降幅达到60%；碳化改变了混凝土的微观形貌，碳化后氢氧化钙晶体数量减少，形成了较多的絮网状和粒状物质，碳化产物碳酸钙填充在混凝土的微观孔结构中，降低了混凝土的孔隙率。