钢筋-混凝土界面区缺陷对钢筋腐蚀行为的影响与修复方法研究

Deterioration of reinforced concrete (RC) structures caused by the corrosion of steel is the major concern in the design, construction and maintenance of RC structures.The corrosion behaviors of steel in concrete are influenced by many factors, such as water to cement ratio,concrete cover,temperature and relative humidity,et al.However, the effect of steel-concrete interface on the corrosion behaviors of steel is rarely found in the literatures so far.In fact,the defects in the steel-concrete interface induced by bleeding water or plastic settlement of concrete significantly influence the chloride threshould level and corrosion process of steel in concrete. In order to study the microstructure of the defects in steel-concrete interface, as well as the effects of the defects on the steel corroion behaviors, we prepar to characterize the microstructures of different interface defects for the following two cases(horizontally and vertically cast steel, top side and under side for horizontally cast steel) by means of X-ray computed tomography and various electrochemical methods(linear polarization resistance and electrochemical impedance spectroscopy, et al). Secondly, it will be considered to track the corrosion process of steel in concrete continually during the three different typical stages, such as the stage for the formation of corrosion products, the stage for the filling the interface defects with corrosion products, and the stage for the formation of crack in concrete cover due to the diffusion of corrosion products. Finally, with the purpose of promoting the duribility and prolonging the service life of RC structures,different synthetical repair methods for the improvement of the interface defects will be specially designed, with the aim to prevent the concrete specimens from steel corrosion in different corrosion stages, and determine the best repair method, the optimal time for repair and the most appropriate time of duration. Based on the study, 1 patent will be applied, and at least 6 scientific papers will be published.

钢筋锈蚀导致的混凝土结构劣化是工程设计、建造与维护过程中的主要难题。混凝土中钢筋的腐蚀行为受诸多因素影响，如水灰比、保护层厚度、温度与湿度等。然而，很少有文献考虑钢筋-混凝土界面区的影响。事实上，由泌水或混凝土塑性沉降导致的钢筋-混凝土界面区缺陷会显著影响钢筋破钝化的氯离子临界值与钢筋的腐蚀过程。为了准确表征界面区缺陷形貌及该缺陷对钢筋腐蚀过程的影响，本研究拟采用X-CT技术与多种电化学技术（线性极化、电化学阻抗谱等）结合的方法无损表征两种情况下（横向成型与纵向成型钢筋、横向成型钢筋上下表面）不同界面区缺陷的微观结构。其次，实时跟踪腐蚀产物的生成、向界面区缺陷填充、向保护层扩散并诱导锈胀裂纹生成这三个关键阶段。最后，设计多种界面区修复组合形式，并对不同腐蚀阶段下的试件修复，确定最优修复形式、最佳修复时间与最适持续时间来提升混凝土结构的耐久性，延长其服役寿命。拟申请专利1项，发表论文≥6篇。

钢筋锈蚀所导致的钢筋混凝土结构劣化是混凝土结构设计、建造与维护过程中主要考虑的因素。纵所周知，暴露于海洋或除冰盐等侵蚀性环境中的钢筋混凝土结构容易出现氯盐诱导的钢筋锈蚀破坏。混凝土保护层由于钢筋腐蚀产物的膨胀而出现开裂、剥落，直至完全失效，这必然将花费巨大的代价对锈蚀钢筋混凝土结构进行维修或重建。然而，很少有文献考虑钢筋-混凝土界面区的影响。事实上，由泌水或混凝土塑性沉降导致的钢筋-混凝土界面区缺陷会显著影响钢筋破钝化的氯离子临界值与钢筋的腐蚀过程。为了准确表征界面区缺陷形貌及该缺陷对钢筋腐蚀过程的影响,本项目应用电化学阻抗谱、X射线CT技术、扫描电镜与能谱分析等测试方法研究了3.5% NaCl溶液侵蚀不同时间后砂浆试样中水平钢筋（相对于成型方向）上下表面腐蚀行为的差异。研究开发并完善了电迁移氯盐加速钢筋腐蚀的方法，并应用X-CT测试技术表征了钢筋-混凝土界面区缺陷对钢筋腐蚀发生与发展过程的影响机理。电迁移氯离子加速钢筋腐蚀法明显加速了混凝土内部钢筋的腐蚀进程，且比阳极通电加速钢筋腐蚀法更符合工程实际情况，是一种行之有效的加速腐蚀方法。结合常用的电化学方法（LPR、EIS与循环极化法）能在短时间内较好地表征钢筋的腐蚀行为，准确地预测钢筋的腐蚀概率与腐蚀速率。应用X-CT测试技术能直观地无损地表征钢筋-混凝土界面区的缺陷。腐蚀产物在钢筋表面的生成及向界面区孔缝扩散均可通过X-CT的灰度值得到直观表述，进一步证实了界面区的缺陷会利于氯盐诱导的钢筋腐蚀，并提供了容纳一定量腐蚀产物的空间。结果表明，钢筋下表面界面区会形成疏松多孔的缺陷，而钢筋上表面界面区无明显缺陷。钢筋下表面缺陷对钢筋的耐蚀性具有双重负面效应，不仅便于氯离子向钢筋表面聚集，还会导致钢筋表面具有保护作用的Ca(OH)2层的缺失。