【作者】 王华；

【导师】 安明喆；

【作者基本信息】 北京交通大学 ， 结构工程， 2014， 硕士

【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。更多还原

【Abstract】 ABSTRACT:Marine concrete structures in coastal areas is suffering the long-term coupling effects of marine corrosion and freeze-thaw cycles, which may result in damage inside, carrying capacity falling and using function degradation. In harsh environment, reactive powder concrete structures with remarkable mechanical properties and excellent durability will have practical significance. In this paper, reactive powder concrete with2%steel fibers was studied. Silica fume was replaced by fly ash and mineral powder.Mass loss, strength loss and chloride ion content in different depthswere measured, separately. Meanwhile, microstructure morphology before and after freeze-thaw cycle was studied by SEM. Based on these results, durability of reactive powder concrete underthe coupling impact of sea water corrosion and freeze-thawcycles was analyzed. The main work and conclusion are as follows:Durability of reactive powder concrete in the coupling impact of marine corrosion and freeze-thaw cycles is far superior to C50concrete. As the mass of reactive powder concrete increased with the coupling impact of sea water corrosion and freeze-thaw cycles, strength loss rather than mass loss is recommended as the evaluation index under Sea water wet/dry cycles.Initial strength of reactive powder concrete will deceased with the incorporation of fly ash or mineral powder, but durability of reactive powder concrete will be improved under the coupling impact of sea water corrosion and freeze-thaw cycles.The coupling impact of sea water corrosion and freeze-thaw cycleshave a great influence on microstructure morphology of concrete SEM results showed that:after the coupling impact of sea water corrosion and freeze-thaw cycles, CH in C50decreased and AFt increased, meanwhile, corrosion products of magnesium with low cohesiveness generate. AFt crystals and F salt exist in the microstructure of reactive powder concrete, but no corrosion product of magnesium was observed.Fly ash and mineral power has a great influence on the freedom chloride ion penetration of reactive powder concrete. Chloride ion diffusion coefficient D was fitted based on Fick’s second law, considering the time dependence of D, it is concluded that, chloride ion diffusion coefficient D has an exponential relationship with time. Prediction model of structural life under the coupling impact of sea water corrosion and freeze-thaw cycles was established. When freeze-thaw cycles damage is the main influencing factors, concrete life of C50is less than30years and reactive powder concrete is more than80years. Monte Carlo numerical simulation was carried on the service life prediction when chloride ion erosion damage is considered as the main influencing factors, the service life which got from the stochastic simulation has a better obedience to the two parameters Weibull distribution, the results indicate that fly ash and mineral power can improve the service life, but content changes of these two admixture have different influence on the life improvement, while increasing the thickness of the protective layer is an important measure to improve concrete service life.更多还原