基于铁碳镀膜光纤光栅传感器的钢筋钝化和脱钝腐蚀监控技术研究

In recent years, the time of corrosion initiation has been considered as the termination of service life for large and important reinforced concrete structures in marine environment (such as Hong Kong-Zhuhai-Macau Bridge). However, most of the optical fiber sensors to monitor steel reinforcement corrosion focus on the active corrosion stage, neglecting the passive stage. Therefore, these optical fiber sensors are unable to monitor both steel passivation and de-passivation stages. This proposal aims to characterize and develop a long period fiber grating (LPFG) sensor for steel passivation/de-passivation monitoring in concrete structures, through depositing a nanometer layer of iron-carbon film on the surface of LPFG. The passivation and de-passivation processes of both the iron-carbon film and the bulk steel bar shall be measured with electrochemical techniques. The evolution of the transmission spectra of the LPFG during the passivation/de-passivation process will be recorded by using an optical sensing instrument. The microstructure and chemical compositions of the passive films formed on both iron film and steel bar are characterized with scanning electron microscopy, energy-dispersive spectroscopy, and x-ray diffraction. The influence of the film thickness on the sensitivity, monitoring range and service life of the passivation/depassivation sensor will also be investigated. The passivation/depassivation sensors will be embedded in ordinary and high performance concrete specimens for long-term durability test to investigate their monitoring sensitivity, sensing range and service life, considering the influences of water cement ratio, concrete cover thickness and high performance admixtures (fly ash, silica fume). The results from this study will provide an option for steel passivation/de-passivation monitoring in large concrete structures in marine environments, and therefore, will be helpful for safety evaluation and service life prediction.

近年来海洋环境下新建的大型结构(如港珠澳大桥)将腐蚀耐久性寿命定为钢筋腐蚀初始时间。而一些基于光纤光栅腐蚀传感器多是监控腐蚀发生之后，因此不能准确地用于钢筋钝化阶段和脱钝过程的监控。本项目拟在长周期光纤光栅表面真空沉积一层微纳米厚的铁碳薄膜制成传感器，用于混凝土中钢筋的钝化/脱钝过程的监控。通过模拟混凝土孔隙溶液中的电化学试验、光学试验和微观化学分析研究光纤光栅钝化/脱钝传感器的敏感性、使用寿命和使用范围。通过普通混凝土海水浸泡试验探讨水灰比和保护层厚度对传感器监控范围和寿命的影响。通过加速氯离子腐蚀试验，研究高性能混凝土添加剂（粉煤灰、硅粉）对钝化/脱钝传感器监控的有效范围和寿命的影响。通过本课题的研究，将解决钢筋钝化阶段和脱钝过程监控的难题。利用本项目的研究成果，可以对普通和高性能混凝土结构中钢筋表面状态进行监控，预测大型结构的腐蚀耐久性寿命，为进一步维护提供依据。

本项目针对海洋环境下将耐久性寿命定为钢筋腐蚀初始时间的大型结构，提出铁碳镀膜长周期光栅光纤传感器用于钢筋钝化阶段及脱钝腐蚀过程监测。通过真空离子溅射和电镀技术，实验室制备了铁碳镀膜长周期光栅光纤传感器，采用扫描电镜、能量谱和原子力显微镜分析了铁碳镀膜的微观结构和化学成分。将铁碳镀膜长周期光栅光纤传感器浸入到饱和氢氧化钙溶液中，研究了钝化膜电阻和电容随时间的变化规律以及铁碳镀膜长周期光栅光纤传感器在钝化膜成长过程中谐振波长的变化规律，建立了钝化膜厚度和铁碳镀膜长周期光栅光纤谐振波长偏移量之间的关系，实现了钝化膜成长的监测。将铁碳镀膜长周期光栅光纤进入到模拟混凝土孔隙溶液中，探明了铁碳镀膜长周期光栅光纤传感器在钝化过程、脱钝点蚀及均匀腐蚀过程中透射光谱的偏移规律，并建立了谐振波长偏移量与表面钝化膜成长、点蚀质量损失以及均匀腐蚀质量损失之间的关系，实现了钝化/脱钝腐蚀过程监测。为了提高腐蚀监测的敏感性，通过离子溅射金膜和交流电镀铁碳薄膜制备了铁碳镀膜长周期光栅光纤传感器，通过电化学试验和光学实验，明确了钝化膜脱钝的临界氯离子浓度，同时采用XPS技术探明了钢筋表面钝化膜的化学成分。将分布式光纤传感器布设在不同保护层厚度的混凝土表面，通过加速腐蚀试验建立了光纤应变和混凝土锈胀裂缝发生发展的关系，实现了混凝土锈胀开裂监测，探讨了传感器的灵敏度、监测范围和使用寿命；同时通过光纤拉拔试验建立了分布式光纤与光纤涂覆层之间的粘结滑移本构模型，基于该模型以及剪滞理论提出了考虑光纤与光纤涂覆层界面滑移机理的裂缝-应变传递模型，为混凝土锈胀开裂监测提供了理论基础。进行了基于多模光纤结构的钢筋腐蚀监测数值模拟和试验研究，建立了多模光纤特征波长和钢筋腐蚀量之间的关系，减低了光纤腐蚀传感器的制造成本。提出了铁碳镀膜长周期光栅光纤传感器的封装方案，为工程应用奠定了基础。