海洋干湿交替区长尺混凝土中钢筋腐蚀演化机制的多尺度原位电化学研究

The corrosion of rebar in concrete is significantly accelerated by the severe corrosive environment in marine dry-wet cycling zone, resulting in the most serious durability problem of the marine infrastructures in this zone. As the large altitude of this zone, at different height position, the difference of dry-wet ratio cause the obvious differences in concrete environmental factors, such as Cl- concentration, relative humidity and oxygen content, etc, which lead to the spatial and temporal difference of the corrosion evolution of rebar in concrete. At present, the kinetics mechanism of corrosion evolution and rust layer evolution rule of rebar in vertical long scale concrete in marine dry-wet cycling zone is not very clear. In this project, the corrosion environment of marine dry-wet cycling zone is simulated using an automatic flood and ebb testing trough. The spatial and temporal distributions and variations of corrosion environment in concrete are monitored in situ using embedded probes. The spatial and temporal corrosion evolution of rebar is monitored in situ using the corrosion potential and electrochemical impedance methods. The distribution and composition of the rust layer are analyzed using SEM, XRD and EPMA methods. According the above methods, the spatial and temporal corrosion evolution and corrosion mechanism of rebar in concrete will be studied under the corrosion environment of dry-wet cycling zone. The influence of corrosive environment on the corrosion evolution of rebar will be revealed. The spatial and temporal evolution rule of corrosion rate of rebar and the distribution and composition of rust layer will be clarified. The corrosion kinetics mechanism during corrosion occurrence and propagation stages will be further revealed. Therefore, this study can provide the theoretical basis for the improvement of the durability and the life prediction of the reinforced concrete structures in marine dry-wet cycling zone.

海洋干湿交替区恶劣的腐蚀环境显著加剧了混凝土中钢筋的腐蚀，导致此区域海洋基础设施的耐久性问题最为严重。由于此区域高度范围大，不同高度因干湿时间比例不同造成混凝土内相对湿度、Cl-浓度及氧含量等环境因素存在明显差异，导致钢筋的腐蚀演化表现出时空尺度的差别。目前，干湿交替区长尺混凝土中钢筋腐蚀演化的动力学机制及锈层演化规律尚不十分清楚。本项目拟采用自动涨落潮试验箱模拟干湿交替区的腐蚀环境，采用预埋探头原位监测混凝土内腐蚀环境的时空分布及变化，利用腐蚀电位及电化学阻抗原位监测钢筋腐蚀的时空演化，并结合SEM、XRD、EPMA等方法表征锈层分布与组成的时空演化，来研究干湿交替区长尺混凝土中钢筋腐蚀的时空演化机制。揭示腐蚀环境差异对钢筋腐蚀演化过程的影响，阐明腐蚀速率及锈层时空演化规律，深入揭示腐蚀发生与发展各阶段的腐蚀动力学机制，为海洋干湿交替区钢筋混凝土结构的耐久性改善和寿命预测提供理论依据。

服役于海洋环境的钢筋混凝土构筑物在干湿交替区的腐蚀，是由氯盐引发钢筋腐蚀导致混凝土劣化的一个特殊且严重的情况。本项目采用电化学原位无损监测技术获取钢筋腐蚀的时空演化规律，得出长尺钢筋的腐蚀演化经历了由初期的钝化阶段，转变为早期的点蚀，再转变为均匀腐蚀三个阶段。并且，相对于钝化阶段和均匀腐蚀阶段，点蚀阶段很短暂，没有形成窄而深的点蚀坑，最终的腐蚀形貌为整个表面上的均匀腐蚀。获得了海洋潮差环境下钢筋的腐蚀速率演化规律，与腐蚀演化过程相对应，表现为早期钝化阶段的不腐蚀，转变为点蚀阶段的加速腐蚀，再转变为均匀腐蚀阶段的稳态腐蚀。预测了锈层分布与组成的演化规律，得出随腐蚀时间延长，钢筋表面锈层由最初局部区域逐渐扩展至整个表面，并逐渐增厚。位于全浸区处的钢筋腐蚀程度最轻，且钢筋表面腐蚀最均匀，由下至上腐蚀速率逐渐加快，位于高潮线之上的飞溅区腐蚀最快，且钢筋表面腐蚀坑最明显，飞溅区的年腐蚀速率约为全浸区的2.5倍。不同区域腐蚀产物组成一致，都由Fe3O4、γ-FeOOH、β-FeOOH和α-FeOOH组成，其中Fe3O4相对含量最高，归因于缺氧混凝土环境下的锈还原作为主要阴极反应，使得FeOOH转变为Fe3O4。阐明了腐蚀发生与发展各阶段的电极反应动力学规律，钢筋在混凝土中的电极反应过程始终由电荷转移过程控制，这主要归因于锈还原作为阴极反应以及混凝土对锈层的挤压使其产生大量裂纹而便于扩散的进行。解释了不同干湿时间比例造成的腐蚀环境差异对钢筋腐蚀演化的影响机制，相对于全浸区，潮差区在干燥过程中混凝土层的氯离子浓度增加，且供氧量增加，使得潮差区腐蚀的阴阳极过程都加速，从而造成腐蚀速率和腐蚀演化过程加速，且干燥时间越长，腐蚀加速越明显。本研究结果能够为海洋干湿交替区钢筋混凝土构筑物的耐久性改善和寿命预测提供理论依据。