【作者】 宋慧；

【导师】 陈建康；

【作者基本信息】 宁波大学 ， 工程力学， 2011， 硕士

【摘要】 海洋环境下,硫酸盐侵蚀是混凝土结构耐久性降低的主要原因之一。当混凝土材料在硫酸盐侵蚀作用下,孔隙中的水化产物会与渗入的硫酸根离子发生反应生成一种称为水化硫铝酸钙晶体,俗称“钙矾石”。由于生成的钙矾石晶体体积大约为反应前水化铝酸钙体积的2.5倍,因此,钙矾石晶体会对混凝土产生挤压作用,当由于钙矾石晶体所产生的内膨胀力所引起的孔隙边缘的拉伸应力超过混凝土材料的抗拉强度时,将导致混凝土材料微损伤的成核。因此,本文主要研究在混凝土材料在硫酸盐侵蚀条件下损伤演化机理,以及由于钙矾石晶体体积膨胀所造成的内膨胀力模型。本文第一章对混凝土材料在硫酸盐侵蚀下耐久性问题的研究进行了综述,主要包括四个部分:混凝土在海水侵蚀下的研究进展;材料损伤理论的研究进展;混凝土材料动态本构关系的研究进展以及本文即将开展的工作。第二章通过细观力学的方法,假定混凝土材料为二相复合材料,再假定混凝土基体的本构模型可以近似用标准线性固体模型来描述,通过对单轴压缩载荷作用下混凝土材料的分析计算发现材料的微损伤成核与孔洞边缘产生的拉伸应力相关,当孔洞边缘的拉伸应力超过材料的抗拉强度时,材料发生微损伤成核。第三章结合已有的混凝土在硫酸盐侵蚀条件下超声波演化及混凝土密度演化结果,分析了不同侵蚀条件下损伤的演化规律。通过分析超声波波速演化实验结果,得出其主要有三个方面的影响因素:一、混凝土材料的继续水化;二、钙矾石晶体的生长对混凝土材料孔隙的填充;三、由于钙矾石晶体的生长产生的内膨胀力所导致微裂纹的演化。结果表明混凝土材料在硫酸盐侵蚀下,侵蚀溶液浓度、混凝土材料的水灰比对Poisson比演化有重要影响。第四章通过运用细观力学方法得到了混凝土在硫酸盐侵蚀条件下的内膨胀力与混凝土材料膨胀应变之间的关系。结果表明,用波尔兹曼函数能够较好的表述整个侵蚀过程当中内膨胀力随时间的演化情况。第五章,采用内变量理论,导出了在单轴应力条件下松弛时间、材料初始弹性模量率相关的非线性粘弹性本构关系的迭代形式,并给出其收敛条件。以此为基础,建立了混凝土材料损伤耦合的非线性粘弹性本构关系。该本构关系可以较好地反映实验结果,并发现材料的松弛时间、材料的初始弹性模量具有明显的率相关性。第六章对全文进行了总结,并对需继续进一步进行的工作进行了展望。更多还原

【Abstract】 Sulfate attack is one of the main factors to reduce the durability of concrete structures in marine environment. When sulfate ions diffuse in pores of concrete, the chemical reaction between the hydration solution of concrete and sulfate ions may take place, therefore, ettringite crystal may nucleate and grow in these pores, and this kind of ettringite is also called as“delayed ettringite”. Usually, volume of delayed ettringite is about 2.5 times bigger than the volume of reactant hydrated calcium aluminate. Therefore, the expansion forces will be induced by delayed ettringite crystal, and the expansion strain of concrete will be produced by the delayed ettringite. If the tensile stress around the voids of concrete caused by the internal expansion force is greater than the tensile strength, the nucleation of damage will take place. Hence, the mechanism of damage nucleation of concrete under sulfate attack is studied, and the model of internal expansion force is also suggested.In chapter 1, problems of concrete durability are summarized, which includes three parts: progress of researches on concrete in marine environment; researches on the damage theory of materials; researches on the constitutive relation of concrete under impact loading.In chapter 2, we assume that concrete is a two-phase composite, and the constitutive relation concrete matrix may be approximately described by the standard linear solid model. The stress analysis about the surface of microvoids in concrete is performed. It is found that the tensile stress may appear at the void surface even the concrete is under the action of uniaxial compressive load. If that tensile stress is greater than the tensile strength of concrete, the nucleation of micro-cracks may take place.In chapter 3, damage evolution of concrete immersed in solution of sodium sulfate of different concentrations is investigated by means of the experiment results of the variation of density and wave velocity of ultrasonic propagated in samples of concrete. The variation of wave velocity of ultrasonic is mainly caused by three factors. The first factor is the continuation of hydration of concrete, and the second one is the effect of delayed ettringite to filling concrete. These two factors may lead to the increase of average modulus of the material and wave velocity of ultrasonic. The third factor is damage evolution, and the wave velocity of ultrasonic will decrease because of the decrease effective modulus due to the erosion damage. The results show that the Poisson’s ratio is significantly affected by the concentration of sulfate solution and water-cement ratio of concrete.In chapter 4, theory of micromechanics is adopted to obtain the relation between the internal expansion stress and expansion strain of concrete under the sulfate attack. The result indicates that Boltzmann foundation can preferably character the evolution of expansion strain and internal expansion stress.In chapter 5, theory of internal variable is used to establish a rate-independent non-liner viscous-elasticity constitutive model, and this model is given by an iterative form. The condition of convergence of the iterative form is analyzed. Based on this model, a new 3-D non-linear viscoelastic constitutive relation of concrete is suggested by considering the damage evolution. It is found that this constitutive model can perfectly describe the experimental results. It is also found that the strain rate will significantly affect the relaxation time and initial modulus of concrete.In chapter 6, the conclusions of this research are summarized, and the further research work is analyzed.更多还原