海水多因素侵蚀下混凝土力学性能劣化特征

发布时间：2018-01-05 12:27

  本文关键词：海水多因素侵蚀下混凝土力学性能劣化特征　出处：《宁波大学》2014年硕士论文　论文类型：学位论文

  更多相关文章： 海水腐蚀 混凝土 损伤演化 劣化

【摘要】：海水中含有大量的氯离子、硫酸根离子和镁离子。这些离子对混凝土的侵蚀作用将会导致混凝土力学性能的劣化以及耐久性的降低。因此,海洋环境下混凝土结构力学性能的演化成为了该领域研究的热点问题。本文对混凝土材料在海水多因素(氯离子、硫酸根离子和镁离子)耦合侵蚀下的强度、动弹模量以及蠕变性能的演化进行了研究。通常情况下,氯离子会侵蚀混凝土中的钢筋(加强筋),硫酸根离子主要侵蚀混凝土。本文重点研究了氯离子对硫酸根离子侵蚀混凝土作用的影响。通过检测氯化钠溶液、硫酸钠溶液和氯化钠-硫酸钠混合溶液腐蚀下的混凝土抗压强度、动弹性模量以及表面硬度的变化,得到了混凝土材料在侵蚀作用下的力学性能演化结果。研究结果表明氯离子在氯盐-硫酸盐侵蚀混凝土的交互作用中,对硫酸根离子侵蚀混凝土的影响可分为三个阶段。第一阶段:氯离子对硫酸根离子侵蚀混凝土的抑制作用随时间的增长呈单调递增趋势;第二阶段:氯离子对硫酸根离子侵蚀混凝土的抑制作用随时间的增长呈单调递减趋势;第三阶段:氯离子对硫酸根离子侵蚀混凝土的抑制作用消失,转变为促进硫酸根离子对混凝土的侵蚀作用,揭示了氯离子对硫酸根离子侵蚀的抑制-转戾现象。论文在第三和第四章对水泥砂浆在硫酸钠、硫酸镁两种溶液侵蚀下的力学性能进行了研究。通过水泥砂浆侵蚀后动弹性模量以及形貌的变化,分析镁离子-硫酸根离子耦合侵蚀混凝土的作用机理。在镁离子和硫酸根离子共同腐蚀下混凝土的损伤可分为三个阶段:Ⅰ.填充混凝土内部孔隙的第一阶段。(延时钙矾石和氢氧化镁固体填充混凝土孔隙,导致混凝土力学性能的增强,故也称该阶段为负损伤阶段。);Ⅱ.钙矾石和氢氧化镁填充导致的混凝土力学性能增强与混凝土内部微裂纹劣化并存的“竞争”阶段;Ⅲ.混凝土内部微裂纹扩展占主导作用的材料劣化阶段。实验结果验证了添加粉煤灰不仅降低了混凝土中C3A的含量,同时改善了混凝土的内部结构,抑制了混凝土的损伤劣化提高了混凝土抗硫酸盐腐蚀的性能。硫酸盐侵蚀下混凝土损伤劣化的新模型。该模型采用微裂纹的数密度表征不同尺度的微裂纹。微裂纹发展的驱动力包括两个方面:远场荷载和侵蚀内膨胀力。根据混凝土的拉伸强度本文给出了微裂纹的起裂条件,再由微裂纹成核率的“白模型”,得到了损伤驱动应力相关的微裂纹成核率方程。在假定微裂纹的长大服从Seaman扩展方程的基础上,结合微裂纹数密度演化的平衡方程,得到了特征线上的微裂纹数密度演化的一阶常微分方程。通过对微裂纹的体积积分,得到了混凝土损伤劣化的新模型。该模型的相关参数由实验结果确定。研究结果表明:本文得到的损伤劣化模型可以比较好地反映混凝土侵蚀损伤演化规律。
[Abstract]:Seawater contains a large number of chloride ions, sulfate ions and magnesium ions. The erosion of concrete by these ions will lead to the deterioration of the mechanical properties of concrete and the deterioration of durability. The evolution of mechanical properties of concrete structures in marine environment has become a hot issue in this field. In this paper, the strength of concrete materials under the coupling erosion of seawater (chloride ion, sulfate ion and magnesium ion) is studied. The evolution of dynamic modulus of elasticity and creep properties has been studied. In general, chloride ions will erode the reinforced bars (reinforced bars) in concrete. The effect of chloride ion on the effect of sulfate ion on concrete erosion was studied. The sodium chloride solution was detected. The changes of compressive strength, dynamic elastic modulus and surface hardness of concrete under corrosion of sodium sulfate solution and sodium chloride sodium sulfate mixed solution. The results of mechanical properties evolution of concrete materials under erosion are obtained. The results show that chloride ion is in the interaction of chloride salt and sulfate erosion concrete. The influence of sulfate ion on the concrete erosion can be divided into three stages: the first stage: the inhibition effect of chloride ion on the sulfate ion erosion concrete shows a monotone increasing trend with the increase of time; The second stage: the inhibition effect of chloride ion on sulfate ion erosion concrete shows a monotone decreasing trend with the increase of time. The third stage: the inhibition effect of chloride ion on sulfate ion erosion concrete disappeared and changed to promote sulfate ion erosion effect on concrete. The inhibition of chloride ions on sulfate ion erosion is revealed. Chapter 3 and 4th of this paper discuss the effect of sodium sulfate on cement mortar. The mechanical properties of magnesium sulfate under two kinds of solution erosion were studied. The dynamic elastic modulus and morphology of cement mortar were changed after erosion. The mechanism of mg ~ (2 +) -sulfate ion coupling erosion concrete is analyzed. The damage of concrete can be divided into three stages under the condition of magnesium ion and sulfate ion corrosion together. I. the first stage of filling the inner pores of concrete. Delay ettringite and magnesium hydroxide solid filled concrete pores. The mechanical properties of concrete are enhanced, so this stage is also called negative damage stage. II. The "competitive" stage in which the mechanical properties of concrete filled with ettringite and magnesium hydroxide coexist with the degradation of microcracks in concrete; The experimental results show that the addition of fly ash not only reduces the content of C3A in concrete, but also improves the internal structure of concrete. A new model for damage deterioration of concrete under sulfate erosion is proposed. The model uses the number density of microcracks to characterize microcracks of different scales. The driving forces of grain development include two aspects:. According to the tensile strength of concrete, the crack initiation conditions are given. Based on the "white model" of microcrack nucleation rate, the damage driven stress related microcrack nucleation rate equation is obtained. It is assumed that the growth of microcrack is based on the Seaman propagation equation. Combining the equilibrium equation of microcrack number density evolution, the first order ordinary differential equation of microcrack number density evolution on characteristic line is obtained. A new model of concrete damage deterioration is obtained. The relevant parameters of the model are determined by the experimental results. The results show that the damage deterioration model presented in this paper can better reflect the evolution law of concrete erosion damage.
【学位授予单位】：宁波大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU528
，

本文编号：1383131