海洋环境混凝土结构耐久性原位监测及其机理研究

The continued durability monitoring of concrete in bad marine environment by using intelligent sensor is important to guarantee the safety of concrete structure. This project aims at developing embedded piezoelectric sensor which is suitable for marine environment to realize the in-situ corrosion monitoring of steel bar in marine environment concrete. The corrosion resistance, stability and reliability will be studied as well as the performance parameters of the sensor, such as resonance frequency, frequency band, sensitivity, frequency response and impedance-frequency feature etc. The fabrication technique of the sensor will also be optimized. The sensor will be embedded into the reinforced concrete structure and the chloride ion penetration in marine environment concrete will also be simulated. Based on stress wave propagation and electromechanical impedance technology, the influences of chloride diffusion, boundary condition and variation of environment condition on receiving ultrasonic wave, acoustic emitting wave and electromechanical impedance characteristic parameters will be studied, and the correlation between corrosion rate, extent of steel bar and kinds of characteristic parameter will also be cleared. The quantitative relationship between kinds of parameters and corrosion damage of steel bar will be obtained. The corrosion mechanism of steel bar in multi-filed coupling effects as well as the corrosion monitoring mechanism of steel bar based on piezoelectric sensor will be disclosed, meanwhile, the damage quantitative index of steel bar corrosion extent will be establised, which can provide theory and application evidence for intelligent monitoring and evaluation of concrete structure in marine environment.

海洋混凝土服役环境恶劣，采用智能传感器对其耐久性进行持续监测是评价其服役寿命及保障结构安全运营的重要前提。本项目拟研发适用于海洋环境的埋置式压电传感器，以期有效实现对海洋环境混凝土结构中钢筋腐蚀的原位监测。研究传感器的耐腐蚀性、稳定性和可靠性，获得谐振频率、频带宽度、灵敏度、频率响应及阻抗频率特性等参数，优化传感器的制备工艺；模拟海洋环境下氯离子侵蚀，将传感器埋入钢筋混凝土结构中，采用应力波传播和机电阻抗技术，研究氯离子扩散、边界条件及环境条件变化等对传感器接收的超声波、声发射波及机电阻抗特征参数的影响规律，明确钢筋腐蚀速率、程度与不同特征参数间的相关性，获得各特征参数与钢筋腐蚀损伤之间的定量关系；揭示多场耦合作用下的钢筋腐蚀机制及基于压电传感器的钢筋腐蚀监测机理，建立反映钢筋腐蚀程度的损伤量化指标，为海洋环境下混凝土结构耐久性的智能监测与评估提供理论和应用依据。

随着我国海洋工程数量及规模的日益扩大，混凝土在使用过程中所暴露的耐久性问题也渐渐突现，在各种因素的综合作用下，很多混凝土结构过早发生损坏，丧失了耐久性能从而严重威胁其正常的使用寿命，采取有效手段对海洋混凝土工程结构进行耐久性监测，评价其使用寿命，这对于保障其安全性具有重要的意义。本项目针对海洋环境混凝土的服役特点，采用切割浇注工艺制备水泥聚合物基压电复合材料。与压电陶瓷相比，压电复合材料的压电电压常数g33比纯压电陶瓷的压电电压常数g33显著增大；随着厚度减小，压电复合材料的串/并联谐振频率、机械品质因数都逐渐变大，而厚度机电耦合系数和声阻抗则变小，且封装后的谐振现象显著减弱。分别制备了适用于钢筋锈蚀监测的机电阻抗传感器和压电超声传感器，采用半浸泡外加电流法模拟自然状态下钢筋锈蚀情况，研究发现，钢筋锈蚀率为2%时，混凝土表面开始渗出铁锈，随着锈蚀的进行，NaCl电解质溶液开始变浑浊，锈蚀率为3%时，混凝土表面出现微裂纹，随着锈蚀的发展，裂纹不断增大增多，锈蚀率到10%时，混凝土表面可以看到明显的裂纹，局部裂纹宽度大于1 mm。不同锈蚀率下机电阻抗传感器的电阻及电抗谱图表明，钢筋锈蚀后，电阻/抗频谱曲线发生漂移，随着锈蚀率增大，电阻/阻峰值对应频率变小，电阻/抗峰值增大；不同锈蚀率下的电阻/抗差值频谱曲线中，电抗差值在500 kHz以后基本为0Ω；选取损伤指数RMSD、MAPD表征混凝土结构中的钢筋锈蚀情况，结果表明，损伤指标值能直观的反映锈蚀程度，RMSD在100-150 kHz，MAPD值在150-200 kHz表现出良好的规律性，损伤指标值随锈蚀率的增大而增大。由锈蚀率下超声传感器的接收波发现，接收波波速、波幅、主频幅值与钢筋锈蚀率之间存在明显的相关性，当钢筋锈蚀率为0%-2%时，随着锈蚀率的增大，接收波波速、波幅、主频幅值迅速减小，锈蚀率为2%-6%时，上述参数虽然也随锈蚀率的增大而减小，但降低的幅度变小；锈蚀率大于6%后，基本不发生变化。