海洋环境下干湿循环和冻融循环对活性粉末混凝土力学性能的影响研究

发布时间：2018-03-18 14:51

本文选题：活性粉末混凝土　切入点：模拟海水　出处：《北京交通大学》2014年硕士论文　论文类型：学位论文

【摘要】：我国沿海地区混凝土结构长期处于海洋环境下,耐久性不足问题普遍存在。活性粉末混凝土作为一种具备超高强度、高韧性以及优异耐久性的新型水泥基复合材料,十分适用于恶劣海洋服役环境下的海工结构及混凝土结构的防护。本文针对结构物在海洋环境下遭受的海水侵蚀、干湿循环和冻融循环等作用,通过模拟海水的于湿循环、模拟海水的冻融循环、去硫酸根模拟海水的冻融循环作用试验,研究了活性粉末混凝土在上述作用下力学性能的变化规律,并结合SEM、XRD等微观方法分析了作用前后试件内部的微观形貌及侵蚀产物。主要工作及结论如下： (1)活性粉末混凝土在模拟海水的干湿循环作用下,随着干湿循环次数的增加,抗压强度呈先上升后下降趋势,劈裂抗拉强度呈现先下降后上升再下降趋势。微观试验表明：海水侵入活性粉末混凝土内部后,发生了镁盐和硫酸盐侵蚀,海水中的氯离子也导致了钢纤维的锈蚀。 (2)活性粉末混凝土材料在模拟海水的冻融循环作用下,材料抗压强度和劈裂抗拉强度总体上都随冻融循环次数的增加而下降；SEM与XRD结果表明：在海水冻融循环作用下,活性粉末混凝土材料内部的孔隙内及缺陷处易发生侵蚀,可观察到明显的钙矾石和石膏,以及少量镁盐和硫酸盐类侵蚀产物。 (3)活性粉末混凝土材料在去硫酸根模拟海水的冻融循环作用下,随冻融循环次数的增加,抗压强度和劈裂抗拉强度总体依然呈下降趋势,但与未去除硫酸根的海水冻融循环作用相比,材料抗压强度下降幅度减小。SEM与XRD试验中没有发现大量的侵蚀产物,仅在试验后期观察到由于材料再水化生成的少量钙矾石,由此可推断在海水冻融循环作用过程中硫酸根离子是引起活性粉末混凝土抗压强度劣化的重要因素之一。
[Abstract]:The concrete structure in coastal areas of China has been in marine environment for a long time, and the problem of insufficient durability is widespread. Reactive powder concrete is a new type of cement matrix composite with ultra-high strength, high toughness and excellent durability. It is very suitable for the protection of marine structures and concrete structures in the severe marine service environment. In this paper, in view of the effects of seawater erosion, dry and wet circulation and freezing and thawing cycle on structures in the marine environment, we simulate the wet circulation of sea water. The mechanical properties of reactive powder concrete (RPC) under the above action were studied by simulating the freezing and thawing cycle of seawater and desulphuric acid radical under the experiment of freezing and thawing cycle of seawater. The microstructure and erosion products of the specimens before and after the action were analyzed by means of SEM XRD and other microcosmic methods. The main work and conclusions are as follows:. 1) under the dry and wet cycle of simulated seawater, the compressive strength of the reactive powder concrete increases first and then decreases with the increase of the times of dry and wet cycles. The splitting tensile strength decreased first and then increased and then decreased. The microscopic test showed that magnesium salt and sulfate erosion occurred after seawater invaded into the reactive powder concrete and the chloride ions in seawater also led to the corrosion of steel fiber. (2) the compressive strength and splitting tensile strength of reactive powder concrete materials decreased with the increase of the number of freeze-thaw cycles under the simulated freeze-thaw cycles of seawater. The results of SEM and XRD showed that: under the action of freeze-thaw cycles in seawater, the compressive strength and splitting tensile strength of the materials decreased with the increase of freeze-thaw cycles. In the interior of reactive powder concrete, ettringite and gypsum, as well as a small amount of magnesium salt and sulphate, are easily eroded in the pores and defects. (3) the compressive strength and splitting tensile strength of reactive powder concrete materials under the action of desulphate simulated seawater freeze-thaw cycle increase with the increase of freeze-thaw cycle times, and the compressive strength and splitting tensile strength still show a downward trend. However, compared with the freeze-thaw cycle without sulfate removal, the decrease in compressive strength of the material was reduced. There was no large amount of erosion products found in the XRD and XRD tests. Only a small amount of ettringite was observed in the later stage of the test because of the rehydration of the material. It can be concluded that sulfate ion is one of the important factors that cause the compressive strength deterioration of reactive powder concrete during the freeze-thaw cycle of seawater.
【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】：TU528

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