硫酸盐侵蚀下水泥基材料微结构模拟及损伤演变

发布时间：2018-01-09 15:25

本文关键词：硫酸盐侵蚀下水泥基材料微结构模拟及损伤演变　出处：《东南大学》2015年博士论文　论文类型：学位论文

【摘要】：硫酸盐侵蚀一直被认为是威胁水泥基材料耐久性的主要原因之一。早期的实验研究在理解硫酸盐侵蚀过程中的膨胀机理方面成果丰硕,大量的模拟计算也在宏观尺度上为预测水泥,砂浆或混凝土的膨胀和损伤破坏奠定了良好的基础。然而,在水泥浆体微结构的尺度上对硫酸盐侵蚀进行模拟却鲜有报道,而这对于从根本上理解水泥浆体的劣化机制至关重要。因此,本文着重对水泥浆体在硫酸盐侵蚀过程中的微结构模拟做了研究。旨在化学方面模拟水泥浆体各水化产物的变化,以及其导致的微结构的演变。此外,本论文还建立了一个耦合扩散-化学-力学的多尺度模型,将硫酸盐侵蚀过程中水泥浆体的宏观性能以及微结构机理有效的关联。该模型既能够在宏观尺度上预测宏观性能的变化,又能在微观尺度上探究硫酸盐侵蚀的机理。硫酸盐侵蚀可以理解为低pH溶液的硫酸盐溶液的侵蚀。因此,本论文首先建立了一个3D微结构模型,用于模拟在低pH溶液不断冲刷下,微结构的演变以及化学方面各水化产物的质量变化。该模型的创新点在于,不仅预测了被人们熟知的溶蚀初期氢氧化钙的溶解,也预测了整个溶蚀过程中C-S-H,铝酸盐相以及硫酸盐等物相的体积及组成成分上的变化。除此以外,我们还将不同阶段的微结构作为输入文件,利用有限元模型和有限差分模型计算了杨氏模量和相对扩散系数随着溶蚀不断进行的改变。为了更好的了解硫酸盐侵蚀过程中的主要膨胀产物(AFt)和主要反应物(AFm)的热力学稳定性,本论文对一个相对较简单的Ca-Al-S-O-H体系进行了研究。首先对已有文献绘制出的在25℃C下的相图重新进行了绘制。不同的是,本文使用的是以吉布斯自由能最小化为基本算法的GEM-Selektor软件以及Nagra-PSI热力学数据库。该算法并不对热力学计算施加额外的约束条件,同时该数据库对水泥基材料体系各物相的热力学性能有更准确的定义。该模型的计算结果与其他文献相一致。随后,研究了碱离子以及体系中的碳含量对AFt和AFm热力学稳定性的影响。本文还讨论了水石榴石溶度积大小的选择对AFm热平衡面的影响,为不同文献关于AFm看似矛盾的报道提出了一个合理的解释。随后,将微结构模型与线性热弹性有限元模型进行耦合,计算了钙矾石在狭窄空间生长时导致的局部体积变形以及局部损伤的产生。该模型应用于计算直接与硫酸钠溶液相接触的表面微结构的演变。结果显示,钙矾石的生长所需要的铝主要依次由单硫型硫铝酸钙,碳铝酸盐以及富含铝的水滑石(如果存在于体系的话)来提供。通过对铝酸盐在微结构空间分布的考察,发现当单硫型硫铝酸钙分布较细,以及在化学方面,提高碳酸盐和镁的含量,均有利于缓解膨胀和损伤。最后,建立了1D的扩散-化学反应-力学模型。该模型首次直接利用结晶压理论,估算微结构局部的体积变形。类似地,通过与热弹性力学的耦合,该模型能够在微结构的尺度上预测损伤的产生,以及直接计算不同深度的微结构的弹性性能和传输性能。这些性能在不经过均匀化处理的情况下,直接被有限差分模型用于更新各离子在传输作用下的浓度分布。该模型的另一个创新点在于首次将硫酸根离子浓度和pH的影响分隔开来,为硫酸盐侵蚀机理提出了新的理解。结果表明,当水泥浆体处于低浓度的硫酸钠溶液中时,总膨胀是由于pH的减小,而非硫酸根离子浓度的增加而引发的。
[Abstract]:Sulfate has been considered to be one of the main reasons for the durability of the threat of cement-based materials. Experimental study on the early expansion mechanism results in sulfate erosion process understanding of the rich, a lot of simulation calculation for prediction of cement on the macroscopic scale, expansion and damage has laid a good foundation for mortar or concrete. However, for there are few reports on the simulation of sulfate in cement paste microstructure scale, and it is essential to understand the mechanism of deterioration of cement paste fundamentally. Therefore, this paper focuses on the cement paste in the sulfate in the process of microstructure simulation is studied. Aimed at the changes of chemical simulation of cement paste the hydration products, and the microstructure evolution of the resulting. In addition, this paper also establishes a coupling diffusion chemical mechanical multiscale model will sulfate erosion The macroscopic properties of cement slurry in the process of the micro structure and associated mechanism of change. The model can predict the macroscopic properties in macro scale, and to explore the mechanism of sulfate erosion in micro scale. Sulfate can understand the erosion of sulfate solution with low pH solution. Therefore, this paper first establishes a a 3D micro structure model for simulation of the low pH solution continuously scouring, the quality change of micro evolution and chemical structure of hydration products. The model innovation is not only to predict the known dissolution of calcium hydroxide solution at the early stage, also predicted the C-S-H whole process of dissolution, volume of aluminate phase and phase composition of sulfate and changes in composition. In addition, we will also micro structure in different stages as the input file, using the finite element method and finite difference model to calculate the The young's modulus and the relative diffusion coefficient with the dissolution constant change. In order to better understand the expansion of the main product in the process of sulfate (AFt) and the main reactant (AFm) thermodynamic stability, this thesis carries on the study of a relatively simple Ca-Al-S-O-H system. Firstly, the existing literature is drawn at 25 DEG C C phase diagram was drawn again. The difference is, this paper are based on the use of Gibbs free energy minimization as the basic algorithm of GEM-Selektor software and Nagra-PSI database. The constraint conditions of thermodynamic calculation of the additional algorithm is not at the same time, the database of thermodynamics, the thermodynamic properties of cementitious materials. There are more accurately defined. The calculated results are consistent with other literature. Then, on the carbon content of alkali ions and in the system of AFt and AFm on thermodynamic stability Ring. In this paper, the water solubility garnet size choice of the influence of AFm on thermal equilibrium is discussed. The different literature about AFm seemingly contradictory reports put forward a reasonable explanation. Subsequently, the micro structure model and linear thermal elastic finite element model are coupled to the local volume deformation caused a growth in the narrow space when calcium. The stone computing and the local damage. The model is applied to calculate the evolution of surface in direct contact with the sodium sulfate solution microstructure. The results showed that the need of ettringite growth of aluminum mainly followed by single sulfur calcium sulphoaluminate, carbon aluminate and aluminum rich hydrotalcite (if it exists in the system words) to provide. Through the investigation of micro structure in aluminate spatial distribution, when single sulfur calcium sulphoaluminate distribution is fine, as well as in chemistry, improve the content of carbonate and magnesium, can relieve swelling And the damage is established. Finally, the diffusion of 1D chemical reaction mechanics model. The model for the first time by the pressure of crystallization theory, estimated volume micro structure of local deformation. Similarly, coupled with thermal elasticity, the model can predict the damage produced in the micro structure of the scale, the micro structure and direct calculation of different depth of the elastic properties and transport properties. These properties without homogenization conditions, directly by the concentration distribution of the finite difference model is used to update the ions in the transmission load. Another innovation of this model is the first time separating effect of sulphate ion concentration and pH. Put forward a new understanding for the mechanism of sulfate attack. The results show that when the cement paste is in sodium sulfate solution in low concentration, the total expansion is due to the decrease of pH, increase rather than the concentration of sulfate ions caused.

【学位授予单位】：东南大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TQ172.1;TB304

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