干湿交替环境下混凝土的氯离子侵蚀与耐久性防护

发布时间：2018-03-14 22:02

本文选题：干湿交替　切入点：混凝土耐久性　出处：《西安建筑科技大学》2013年博士论文　论文类型：学位论文

【摘要】：氯离子侵蚀引起的钢筋锈蚀，是导致海洋环境下混凝土结构耐久性破坏的主要原因。浪溅区、潮汐区的混凝土因遭受干湿交替作用下的氯离子侵蚀，耐久性劣化情况更为严重。首先，针对干湿交替环境下混凝土结构的氯离子侵蚀，对氯离子在混凝土结构中的传输机理进行了系统分析，构建了氯离子的对流—扩散传输模型，并通过干湿交替循环试验进行验证。然后，利用线性极化法进行了钢筋锈蚀状态的检测，测定了干湿交替环境下混凝土结构临界氯离子浓度值。接下来，考虑收缩和荷载作用，深入探讨了损伤混凝土中的氯离子传输规律，建议使用硅烷或工程用水泥基复合材料（ECC）作为混凝土结构表层防护材料。最后，基于可靠度理论提出了满足目标可靠指标的耐久性概率设计方法，为干湿交替环境下混凝土结构耐久性设计提供参考依据。主要研究内容和成果如下：（1）干湿交替环境下混凝土的氯离子传输机理氯离子主要通过毛细吸收和扩散等方式对混凝土造成侵蚀。首先，根据干湿交替环境下混凝土的工程实际情况，建立了氯离子的对流—扩散传输模型，并且采用有限差分格式进行了方程求解，进行了氯离子干湿交替侵蚀混凝土的试验。试验中所测定的氯离子含量分布与数值模拟的结果吻合。这表明，对流—扩散传输模型较好反映出了干湿交替环境下混凝土结构的氯离子传输规律。数值模拟和试验结果都说明干燥—润湿时间比是氯离子峰值和渗透深度的关键影响因素，随着干燥—润湿时间比例增加，氯离子峰值呈现出增大的趋势，渗透深度也在变大。（2）干湿交替环境下的临界氯离子浓度氯离子临界浓度是影响海洋环境下混凝土结构服役寿命的一个关键参数。制备了四种不同水胶比的混凝土试件，使用5%的NaCl溶液，在60%的相对湿度下，进行了干湿循环试验。试验中，依据钢筋腐蚀电流密度对锈蚀状况进行定时检测，测定了锈蚀发生时混凝土不同深度处的氯离子含量。最后，确定了具有90%保证率的干湿交替环境下不同混凝土的临界氯离子浓度值。考虑碳化程度进行氯离子含量的测定和临界氯离子浓度值的统计分析，使得试验更接近工程实际，提高了试验结果的科学性和适用性，也为进一步进行干湿交替环境下混凝土结构的试验研究提供了参考。（3）表层防护后混凝土中的氯离子传输由混凝土的外部荷载、早期收缩而产生的裂缝，为氯离子的渗入提供了便利通道，，加速了钢筋锈蚀，降低了混凝土结构的耐久性能。通过混凝土加载和约束收缩条件下的氯离子侵蚀试验，研究了损伤混凝土中的氯离子传输规律。混凝土中氯离子扩散系数随拉应力的增加而增加，70%应力水平后急剧增大；氯离子侵蚀量随混凝土裂缝宽度增加而增加；在同样加载和约束收缩条件下，经硅烷或ECC表面防护的混凝土比普通混凝土具有更好的抗侵蚀性能。（4）表层防护后混凝土的耐久性设计依据氯离子对流—扩散传输模型的数值模拟与试验测得的临界氯离子浓度值，基于可靠度理论，考虑荷载和早期收缩产生的损伤因素，提供了具体的概率计算方法，以解决干湿交替环境下混凝土表层防护的耐久性设计问题。对于采用硅烷或ECC作为表面防护材料的混凝土结构，以氯离子扩散系数和保护层厚度作为主要设计参数，对混凝土结构进行了表层防护的耐久性设计，以满足设计使用年限内的目标可靠指标。
[Abstract]:Reinforcement corrosion caused by chloride ion erosion is the main cause of failure of the durability of concrete structure in marine environment. The splash zone, tidal zone of concrete due to alternate chloride ion erosion and deterioration of durability situation is more serious. Firstly, according to the concrete structure under the Chloride Erosion of the wet dry. The transmission mechanism of chloride ion in concrete structure are analyzed systematically, constructs the convection diffusion model of chloride transport and verified by cyclic alternating wet and dry test. Then, the detection of steel corrosion condition using linear polarization method, the critical concentration of chloride ion in concrete structure under dry wet alternation was determined. The next value consider, shrinkage and load, discusses the chloride ion transport law of damage in concrete, recommend the use of silane or engineering cementitious composites (ECC) as Finally, based on the theory of reliability, a probabilistic design method for durability of concrete structures is proposed, which provides a reference for durability design of concrete structures under dry and wet alternative environment. The main contents and achievements are as follows:
(1) the mechanism of chloride transport in concrete under dry and wet environment
The chloride ion mainly through capillary absorption and diffusion of concrete caused by erosion. First of all, according to the actual condition of concrete under the environment of alternating wet and dry, a convection - diffusion model of chloride transport and the use of the finite difference scheme of the equation, for the chloride ion erosion of concrete. The alternate test was in simulation experiments of distribution of chloride ion content and numerical results are in good agreement. This indicates that the convection diffusion transfer model better reflects the environment of concrete chloride ion transport law. Alternate numerical simulation and experimental results show that the drying - wetting time ratio are the key factors that affect the peak value and penetration depth of chloride, with dry - wetting time was increased, the chloride peak increases, the penetration depth is also larger.
(2) the critical chloride concentration in the alternating dry and wet environment
Critical concentration of chloride ions is a key parameter affecting the service life of concrete structures in marine environment. The preparation of four kinds of concrete with different water binder ratio of the specimen, using 5% NaCl solution, the relative humidity of 60%, the dry wet cycling test. In the test, on the basis of corrosion current density on the timing detection the corrosion of chloride ion content at different depth of concrete corrosion occurs is determined. Finally, determine the rate of 90% that the alternate critical chloride concentration of concrete under different environmental value. Considering the degree of carbonation were used for statistical analysis of chloride ion content determination and critical chloride concentration, which is more close to the engineering test actually, improves the scientificity and applicability of the test results, but also for the further study of the concrete structure of alternating wet and dry environment to provide a reference.
(3) chloride transport in concrete after surface protection
By the external load of concrete cracks, early shrinkage, provides a convenient channel for chloride ion penetration, accelerate the steel corrosion, reduce the durability of concrete structures. By chloride ion loading and restrained shrinkage of concrete under erosion test, studied the chloride ion transport law of damage in the concrete. The concrete increase the chloride ion diffusion coefficient with tensile stress increased, stress level increases sharply after 70%; chloride ion erosion of concrete crack width increases; under the same loading conditions and restrained shrinkage, the protective silane or ECC concrete has better corrosion resistance.
(4) durability design of concrete after surface protection
Based on the critical chloride concentration of experiment and numerical simulation of chloride ion diffusion convection transport model of measured values, based on the theory of reliability, considering damage factors and early shrinkage load, calculation method provides specific probability, to solve the problem of durability design of concrete surface protection of the environment. For the use of silane or alternate ECC as the concrete surface protection materials, the chloride ion diffusion coefficient and the thickness of the protective layer as the main design parameter, the concrete structure of the durability design of surface protection, to meet the design target reliability index number.

【学位授予单位】：西安建筑科技大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU375

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