早龄期受冻水泥基材料的孔结构、抗渗性和强度研究

发布时间：2018-07-28 12:09

【摘要】：混凝土的早期冻害会造成其内部孔结构的严重损伤,而混凝土的孔结构特征强烈地影响着混凝土材料的抗渗性能和力学性能。研究孔隙微观结构的变化,探讨早期受冻环境下混凝土的强度和抗渗性能的发展规律,掌握早期冻害的作用过程具有重要的理论意义和工程应用价值。本文将分形理论应用到早期受冻水泥基材料的研究中,根据分形维数的无标度性对孔径进行自主划分,并验证分形维数的物理意义即定量描述孔结构的复杂程度。研究了早期受冻条件下,不同试验因素的水泥基材料氯离子扩散和强度的发展变化规律,并基于孔结构给出了变化规律的内在机制,研究了早期受冻温度对水泥基材料孔结构发展规律的影响,并阐述了早期冻害的作用过程。试验结果表明,早期受冻水泥基材料的孔结构具有明显的分形特性,利用无标度性对孔径进行自主划分,发现其孔径范围不受试验因素的影响,但净浆和砂浆的孔径分布并不相同。在早期受冻的条件下,对于预养24h的净浆,10~350nm的孔径影响早期强度增长,350~6000nm的孔径影响后期强度的增长;对于预养24h的砂浆而言,10~2000nm的孔径是影响强度的主要因素;预养不充分对净浆强度造成的损失非常大,并且预养24h后大于6000nm的孔径基本趋于稳定;而砂浆中大于2000nm的孔径在影响强度的同时,也受预养时间的影响,同样预养24h之后该范围内的孔径趋于稳定。每个区域内的孔径对水泥基材料的抗渗性能都有一定的影响,对于预养24h的砂浆,10~100nm范围内孔径作用效果更大,而对于预养24h的净浆,10~6000nm范围内的孔径则是影响氯离子扩散系数的主要因素。早期受冻会改变水泥基材料内部的孔径分布,其中受冻温度会影响孔径的变化范围,研究发现早期受冻的作用过程是孔结构劣化和填补修复同时进行的过程,在这过程中液态水扮演着重要的角色,水分的迁移、冰晶的形成与扩散对孔结构造成了不可恢复的损失。
[Abstract]:The early freezing damage of concrete will cause serious damage to its internal pore structure, and the pore structure characteristics of concrete strongly affect the impermeability and mechanical properties of concrete materials. It is of great theoretical significance and engineering application value to study the change of pore microstructure, to discuss the development law of strength and impermeability of concrete under early freezing environment, and to master the action process of early freezing injury. In this paper, fractal theory is applied to the study of early frozen cement based materials. According to the scale-free fractal dimension, the pore size is divided independently, and the physical meaning of fractal dimension is verified, that is, quantitatively describing the complexity of pore structure. The development and variation of chloride ion diffusion and strength of cement based materials under the condition of early freezing were studied, and the internal mechanism of the change law was given based on the pore structure. The effect of early freezing temperature on the development of pore structure of cement based materials was studied, and the process of early freezing injury was described. The experimental results show that the pore structure of the early frozen cement-based material has obvious fractal characteristics, and the pore size range is not affected by the experimental factors by using the scale-free property to divide the pore size independently. But the pore size distribution of mortar and mortar is different. Under the condition of early freezing, the pore size of 10350nm of pre-cultured slurry for 24 hours affects the increase of early strength, the pore size of 350,600 nm affects the increase of later strength, and the pore diameter of 102000nm is the main factor affecting the strength of mortar after 24 hours of pre-culture. The loss of pulp strength caused by insufficient pre-culture is very large, and the pore size larger than 6000nm tends to be stable after 24 hours of preconditioning, while the pore size larger than 2000nm in mortar affects the strength as well as the preconditioning time. The aperture in this range tends to be stable after 24 hours of preconditioning. The pore size in each region has a certain effect on the impermeability of cement-based materials, and it is more effective in the range of 10100 nm for pre-cultured mortar for 24 hours. The pore size in the range of 106000nm is the main factor affecting the diffusion coefficient of chloride ions. Early freezing will change the pore size distribution in cement based materials, in which freezing temperature will affect the range of pore size. It is found that the process of early freezing is the process of pore structure deterioration and repair simultaneously. Liquid water plays an important role in this process. The migration of water and the formation and diffusion of ice crystals cause irrecoverable loss of pore structure.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU528

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