【作者】 陈思佳；

【导师】 刘西拉； 孙国钧； 宋晓冰；

【作者基本信息】 上海交通大学 ， 固体力学， 2013， 博士

【摘要】 钢筋混凝土结构是目前我国以及世界上各个国家基础建设中应用最广泛的结构形式，其耐久性问题正逐渐得到各个国家的重视。而对于我国三北地区以及世界上其他寒冷地区，冻融循环又是影响到钢筋混凝土结构耐久性的最主要的因素。因此，冻融环境下钢筋混凝土结构的耐久性研究是钢筋混凝土耐久性研究中非常重要的一部分内容。本文从冻融环境对钢筋混凝土结构耐久性的直接影响和间接影响这两方面展开研究，进行了如下工作：一、冻融循环对钢筋混凝土结构耐久性的直接影响，考虑的是冻融循环对混凝土的直接冻害。本文通过机理分析，结合实际冻融环境下混凝土一般承受压力的情况，通过自制外压力设备，针对外压力作用下混凝土试块的抗冻性能及强度衰减规律进行了试验研究，并深入讨论了外压力、水灰比及引气剂对试验结果的影响机制。基于试验结果和机理分析，本文最终提出了冻融环境下，受外压力混凝土的抗压强度退化模型，并结合其他研究人员的实验室试验数据以及现场检测结果，对本文模型进行了验证。二、冻融循环对钢筋混凝土结构耐久性的间接影响，考虑的是冻融循环对钢筋混凝土其他耐久性问题的影响。本文主要着眼于氯离子引起的钢筋锈蚀问题，其中一个非常重要的问题就是氯离子的入侵混凝土问题。本文从冻融环境下氯离子入侵混凝土的机理分析入手，设计实施了冻融环境下的氯离子自然浸泡扩散试验，并深入讨论了冻融循环、水灰比、粉煤灰及引气剂对试验结果的影响机制。结合试验结果得到了冻融环境下氯离子有效扩散系数的时变模型，并在此基础上最终提出了在冻融环境下的氯离子入侵混凝土模型；最后，结合其他研究人员的实验室试验数据以及现场检测结果，对本文模型进行了验证。三、冻融循环对氯离子引起的钢筋锈蚀影响研究中，另一个非常重要的问题就是钢筋锈蚀的临界氯离子浓度问题。本文从钢筋腐蚀的电化学腐蚀原理研究入手，明确了：在混凝土这样的特定环境中，氯离子入侵导致钢筋脱钝的本质原因是，钢筋的腐蚀电位超过了钢筋的点蚀电位。并在此基础上，设计实施了冻融环境下以恒电位控制、宏电流测量判断钢筋脱钝的临界氯离子浓度试验。结合试验结果，本文讨论了冻融循环、点蚀电位、水灰比以及引气剂对临界氯离子浓度的影响。根据本文低温下的试验结果和以往常温和高温下的研究结果，得到了低中高全范围温度与临界氯离子浓度的关系，并在此基础上讨论了冻融环境对钢筋脱钝的整体影响。在以上研究过程中，充分发挥了试验在宏观现象与细观机理之间的桥梁作用，有效地解决了研究中的难点问题。并且，对文章中提出的各计算模型都进行了从现场检测到实验室快速试验的验证，确定了模型的可靠性和在实际工程中的适用性。感谢国家自然科学基金(No.50678101)和上海自然科学基金(No.11ZR1417400)对本文研究的资助。更多还原

【Abstract】 Reinforced concrete structures are the most popular structures in infrastructureconstruction, and the durability of reinforced concrete structure has become widely concernednow. In cold regions, the freeze-thaw resistance of reinforced concrete structures is the mostimportant parameter to define durability. It is clear that the research of durability of reinforcedconcrete under freeze-thaw cycles is very important. In the present dissertation, two aspects ofdirect and indirect influence of freeze-thaw cycles on the durability of reinforced concretestructures are given as follows:1． The direct influence of freeze-thaw cycles on the durability of reinforced concretestructures means the influence of freeze-thaw cycles on concrete directly. It is well knownthat most of concrete structures in cold regions are subjected to both external loads andfreeze-thaw cycles. In the present dissertation, the frost resistance and compressivestrength degradation of concrete under the simultaneous action of compressive load andfreeze-thaw cycles were experimentally investigated by specially designed apparatus.Also, the influence of external loads, w/c ratio and air entrainment on experimental resultswas discussed respectively. Based on the experimental results and mechanism analysis, amodel was suggested to predict the compressive strength degradation of concrete underthe simultaneous action of compressive load and freeze-thaw cycles, and the model wastestified by the data obtained from both situ and laboratory.2． The indirect influence of freeze-thaw cycles on the durability of reinforced concretestructures means the influence of freeze-thaw cycles on the other durability problems of reinforced concrete. In the present dissertation, author focuses on chloride inducedcorrosion, in which chloride ingress into concrete is one of the most important problems.Firstly, the mechanism of ions transport operating in concrete and the parameters thatdefine them were discussed. And then, the experiment of chloride ingress into concreteexposed to freeze-thaw cycles was carried out by the natural diffusion method. Also, theinfluence of freeze-thaw cycles, w/c ratio, fly ash and air entrainment on experimentalresults was discussed respectively. With the experimental results, a time dependent modelof effective diffusion coefficient was established, and based on which, a model wassuggested to predict chloride ingress into concrete under freeze-thaw cycles. Also thepredicting model was testified by the data obtained from both situ and laboratory.3． Another important problem in chloride induced corrosion research is the research ofchloride threshold level (CTL) for corrosion initiation. In the present dissertation, theinfluence of freeze-thaw cycles on CTL was discussed. Firstly, the electrochemicalmechanism of corrosion of steel in concrete was reviewed. And the conclusion wasobtained that the essential condition for depassivation of steel in concrete was corrosionpotential exceeding pitting potential. Based on the conclusion, experiment of CTL of steelin concrete specimens under freeze-thaw cycles was carried out. And in the experiment,the potentiostatic and macro current testing methods were used to control and check thecorrosion state of steel. With the experimental results, the influence of freeze-thaw cycles,pitting potential, w/c ratio and air entrainment on CTL was discussed respectively. At last,with the research of CTL under normal temperature and high temperature, the relationshipbetween CTL and full range of temperature (low, normal and high temperature) wasobtained, and based on which, the influence of freeze-thaw cycles on steel depassivationwas discussed.In the previously mentioned research works, several difficult problems were solvedsuccessfully through experiments. All models established in the present dissertation were testified by data obtained from situ and laboratory, which enhanced the reliability andapplicability of models in practice.The author wishes to express his appreciation for the support of the National NaturalScience Foundation of China (No.50678101) and Natural Science Foundation of Shanghai(No.11ZR1417400).更多还原