海水冻融循环作用下活性粉末混凝土的耐久性研究

发布时间：2018-01-27 17:04

本文关键词： 活性粉末混凝土海洋环境冻融循环耐久性微观分析寿命预测　出处：《北京交通大学》2014年硕士论文　论文类型：学位论文

【摘要】：摘要：在长期海水侵蚀和冻融循环的耦合作用下,沿海寒冷地区的海工混凝土结构会出现内部损伤、承载力下降以及使用功能退化等耐久性问题。为了延长这种恶劣环境下结构的使用寿命,将具有良好力学性能和优异耐久性的活性粉末混凝土用于海洋建筑结构中的现实意义巨大。本文通过试验研究和理论分析,在确定活性粉末混凝土中钢纤维最优体积掺量2%的基础上,以粉煤灰、矿粉替代硅粉掺量为主要变化参数,以C50高性能混凝土为对比试件,测定了各组试件的质量损失率、抗压强度损失率和不同深度处氯离子含量,并利用SEM研究了海水冻融循环前后试件内部的微观形貌变化,初步探索了海水冻融循环作用下活性粉末混凝土的耐久性,主要工作及结论如下：海水冻融循环作用下,活性粉末混凝土的耐久性远优于C50高性能混凝土。由于活性粉末混凝土质量随着海水冻融循环作用的增加有所提高,不建议使用质量损失率作为其抗海水冻融循环作用的评价指标,建议选用抗压强度作为其抗海水冻融循环作用的评价指标。粉煤灰或矿粉的掺入使活性粉末混凝土初始强度降低,同时,这两种矿物掺合料都能够显著提高活性粉末混凝土在海水冻融循环作用下的耐久性。海水冻融循环作用对混凝土微观形貌产生的影响很大。SEM实验结果表明：海水冻融循环作用后,C50高性能混凝土内CH减少,AFt增多,还有黏聚性较低的镁盐类腐蚀产物生成；活性粉末混凝土有AFt晶体以及F盐生成,未观察到明显的镁盐类物质。粉煤灰和矿粉对活性粉末混凝土中自由氯离子渗透性能的影响较大。结合Fick第二定律拟合出活性粉末混凝土的氯离子扩散系数D,最后再考虑扩散系数D的时间依赖性对其进行修正,结果表明活性粉末混凝土氯离子扩散系数随时间变化呈指数关系。建立冻融和氯离子侵蚀耦合作用下的结构寿命预测模型。当冻融破坏为主要影响因素时,C50高性能混凝土使用寿命小于30年,活性粉末混凝土使用寿命均大于80年；当氯离子侵蚀破坏为主要影响因素时,对使用寿命进行了Monte Carlo数值模拟,发现随机模拟得到的使用寿命较好的服从两参数的Weibull分布,结果表明粉煤灰和矿粉均能够提高使用寿命,但二者掺量变化使用寿命提高的规律不同,同时,增加保护层厚度是提高使用寿命的重要措施。
[Abstract]:Absrtact: under the coupling of seawater erosion and freeze-thaw cycle for a long time, the marine concrete structure in the cold coastal area will appear internal damage. Durability problems such as reduced bearing capacity and degradation of service functions. In order to prolong the service life of structures in this harsh environment. It is of great practical significance to use the reactive powder concrete with good mechanical properties and excellent durability in marine building structures. This paper is based on experimental research and theoretical analysis. On the basis of determining the optimal volume content of steel fiber in reactive powder concrete (RPC) 2%, the main variable parameters are fly ash and mineral powder instead of silica fume, and C50 high performance concrete as contrast specimen. The mass loss rate, compressive strength loss rate and chloride content at different depths were measured, and the microstructure of the specimens before and after seawater freeze-thaw cycle was studied by SEM. The durability of reactive powder concrete under seawater freeze-thaw cycle is preliminarily explored. The main work and conclusions are as follows: The durability of reactive powder concrete is much better than that of C50 high performance concrete under the action of seawater freeze-thaw cycle, because the quality of reactive powder concrete increases with the increase of seawater freezing and thawing cycle. It is not recommended to use the mass loss rate as the evaluation index of its anti-seawater freeze-thaw cycle. It is suggested that the compressive strength should be selected as the evaluation index of the anti-freezing and thawing effect of seawater. The initial strength of reactive powder concrete is reduced by the addition of fly ash or mineral powder, and at the same time. Both of these mineral admixtures can significantly improve the durability of reactive powder concrete under seawater freeze-thaw cycle. The effect of seawater freeze-thaw cycle on the microstructure of concrete is very great. SEM results show that the Ch in C _ (50) high performance concrete increases after seawater freeze-thaw cycle. There is also the formation of magnesium salt corrosion products with low agglomeration. AFt crystals and F salts were formed in the reactive powder concrete, and no obvious magnesium salts were observed. Fly ash and mineral powder have great influence on the free chloride ion permeability in reactive powder concrete. The chloride diffusion coefficient D of reactive powder concrete is fitted with Fick's second law. Finally, considering the time dependence of diffusion coefficient D, the results show that the chloride ion diffusion coefficient of reactive powder concrete varies exponentially with time. The structure life prediction model under the coupling of freezing and thawing and chloride ion erosion is established. When freeze-thaw failure is the main influencing factor, the service life of C50 high performance concrete is less than 30 years. The service life of reactive powder concrete is more than 80 years. When chloride erosion is the main factor, the Monte Carlo numerical simulation is carried out for the service life. It is found that the better service life obtained by random simulation is from the Weibull distribution of two parameters. The results show that both fly ash and mineral powder can improve the service life. However, the law of increasing service life is different between them. At the same time, increasing the thickness of protective layer is an important measure to improve the service life.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TV431

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