城市混凝土桥梁盐冻病害调查与研究

Investigation and Study of Durability of Bridge under Salt Scaling

为了探究盐冻作用下城市混凝土桥梁的破坏特征及评价盐冻环境混凝土桥梁主体结构的服役现状,通过现场调研、检测、取样和室内试验,研究了混凝土的主要物理力学性能、氯离子质量分布和表层混凝土及钢筋锈蚀物的微观结构.结果表明:盐冻作用下混凝土桥梁使用13a以后,其主体结构发生了严重的除冰盐冻融破坏和钢筋锈蚀破坏,混凝土的氯离子结合能力很低,自由氯离子浓度很高,钢筋锈蚀物中物理吸附了大量的氯离子,且氯离子迁移多堆积于靠近钢筋表面的混凝土层,其总氯离子质量高于钢筋表面及受力钢筋间混凝土近2倍;实际混凝土结构工程在盐冻作用下,混凝土保护层的氯离子浓度分布规律并不符合Fick第二扩散定律;在盐冻环境作用下进行混凝土桥梁结构的耐久性设计时,必须提高其抗盐冻能力、抗氯离子扩散渗透能力,氯离子扩散模型必须考虑表层效应.

For the purpose of exploring the failure characteristics of urban concrete bridge under deicing salt scaling and evaluating the existing structure condition, main physical and mechanical properties of the ma- terial, chloride ion concentration distribution, and the microstructure of concrete cover and corroded steel bar were studied through site investigation, sampling and laboratory experiments. The results show that serious salt freezing damage and steel bar corrosion occur in the main structure of the bridge, when the bridge has been used under deicing salt scaling for 13 years. Chloride ion binding capacity of concrete isquite weak; meanwhile, free chloride ion concentration is very high. The products from bar corrosion ad- sorb a large amount of chloride ions physically. Microstructure analysis indicates that chloride ions migrate to the interface of rebar and concrete, and its total chlorine concentration is almost twice that in other loca- tion, such as surface or interface of steel bars. The distribution behavior of chloride ion concentration of concrete cover does not fit the Fick＇s second diffusion law. Therefore, durability design of bridge struc- tures under deicing salt scaling needs to improve salt freezing resistance and chloride ion permeability, mo- reover, surface effects must be taken into account in the chloride diffusion model when life design is carried on.