【作者】 戴伟；

【导师】 水中和；

【作者基本信息】 武汉理工大学 ， 材料学， 2012， 博士

【摘要】 水泥的水化及微结构演变过程对于水泥基材料的性能有着重要影响。近200年来,材料学家对这一课题进行了深入研究并取得了许多有意义的成果。然而由于水泥水化过程太过复杂,至今人们对水化机理的了解仍不十分透彻,对水化产物微观尺度结构特性也缺乏深入的认识。本文以分子模拟为主要研究手段,对水泥水化过程中的一些问题进行了理论探讨,如CaO与H2O的作用机制、C3S的掺杂改性、C-S-H凝胶的微观结构、水化反应的影响因素等。此外,所有计算得到的结果均通过与试验数据的比对以验证所选算法和模型的有效性,这一新型的研究手段对今后按工程需求设计水泥基材料具有很大的潜在价值。作为水泥熟料中的重要化学成分之一,CaO与H2O分子的相互作用情况对于我们了解更为复杂的水泥单矿的水化反应具有重要的参考意义。通过量子力学的第一性原理计算,可以发现CaO(100)完美晶面较体相发生了明显表面极化,从而具有更高的反应活性并能够自发地吸附H2O分子并与之化学成键。当覆盖度为1/4ML和1ML时,H2O分子在CaO(100)完美表面最稳定的吸附位点是桥位,而在1/2ML覆盖度下穴位则成了最稳定的吸附位点。高岭上以其优异的吸附性能被广泛应用于水泥基材料领域,通过巨正则蒙特卡罗法,系统研究了不同条件下(温度,压强及铝硅比)高岭上体系对水分子吸附特性的演变规律。在其它条件相同的情况下,压强的增加,可以明显促进高岭土对水分子的吸附,而温度的升高则不利于吸附量的提升。经铝离子掺杂改性后,高岭土体系的活性提高明显,而为平衡体系电价所引入的阳离子会造成高岭土体系内微孔尺寸的改变。对于水泥水化过程中的主要反应物(C3S)和产物(C-S-H凝胶),首先以测试手段获得的结构参数为基础构建起合理的模型,通过分子动力学模拟和蒙特卡罗模拟较为成功地制备出无定形态的C-S-H凝胶。以所得结构为基础,分别考察了CuO掺杂C3S和苯乙烯—丙烯酸酯改性C-S-H凝胶的过程。为降低熟料C3S烧成温度而引入的CuO,并不会改变整个晶胞的结构而只是引起微小的局部变化。当CuO的掺量较低时,其仅仅通过溶解的方式进入晶格,不涉及任何化学变化,而当掺量达到3%时,CuO便可能会与C3S发生固溶并生成新的物相。通过分子动力学模拟和蒙特卡罗模拟制得的C-S-H凝胶体系,具有明显的短程有序而长程无序的非晶态结构特性,并且不同钙硅比下的最终结构趋于一致化。此时体系中的Si原子与O原子以4配位的形式存在,这意味着硅氧四面体仍为基本的结构单元,它们彼此之间通过共用的桥氧原子形成链状结构。为改性C-S-H凝胶而引入的苯乙烯—丙烯酸酯有机分子能够较好地与原有体系相溶,并使得体系的可压缩性明显增大,而体积模量和剪切模量明显下降。最后,以连续水化介质模型为基础,系统研究了水泥熟料品质及水灰比对水泥水化过程和微结构演变的影响规律。通过将水泥颗粒简单视为不同粒径的球体,可以将复杂的水化过程等效为球形颗粒与水反应后的向外扩展过程。通过有效的计算模拟,便可以将水泥水化过程及微观结构演变过程以直观的方式进行呈现。在所建立的普硅、低碱和高碱水泥模型中,我们可以清晰地观察到不同水化龄期(3小时、6小时、3天、7天及28天)的微观结构分布情况,各水化产物和孔隙的分布与实际情况吻合较好。此外,研究体系的水化度和孔隙率均随水灰比的增加而增大,但弹性模量呈下降趋势。无论在普硅、低碱还是高碱水泥体系里,模拟得到的弹性模量均大致相同,而水灰比和孔隙率的数值则差别较大。通过本论文的研究内容,可以增进对水泥水化过程及产物结构特性微观层面上的理解,同时也进一步丰富了分子模拟的应用领域。在目前水泥基材料的分子模拟研究仍较为缺乏的情况下,这一领域在未来必将有更大的发展空间。更多还原

【Abstract】 The hydration process and microstructure development of cement have significant influence on the properties of cement-based materials. In the recent200years, experts of material got many valuable achievements through the research of this topic. However, the hydration process of cement is such complex that the hydration mechanisms couldn’t be totally understood and the microstructural characteristics couldn’t be obtained. Using molecular simulation as main method, some issues of cement hydration process were discussed in this paper, such as the mechanisms of the reaction of CaO and H2O, the doping modification of C3S, the microstructure of C-S-H gel, the factor which effects the hydration process etc.Besides, the validity of chosen algorithm and model were verified through the comparison of experimental data with calculated result, this new research method which has great potential value for designing the cement-based material according to engineering requirements.To understand more intricated hydration of cements clinker minerals, the interaction process of CaO, one of the most important ingredients of cement clinker, and H2O is an important implication. Calculating through first principle of quantum mechanical, we found the perfect surface of CaO(100) polarized observably compared to bulk phase, and then this surface got higher reactivity which made it adsorb H2O molecule spontaneously and form chemical bonds. At the coverage of1/4ML and1ML, the most stable adsorption site is bridge site, while the coverage is1/2ML, hole site becomes the most stable adsorption site.Kaolin was applied to cement material widely because of its outstanding adsorptivity. The water adsorptivity evolution pattern of kaolin system was studied by Monte Carlo method. When other conditions keep the same, the increasing pressure will improve the adsorption of water, while the increasing temperature will prevent adsorption. Under the admixture effects of aluminium ion, the activity of kaolin system was enhanced obviously, while the introduced positive ion to counter-balance electrovalence will change the aperture of kaolin.The reasonable model of main reactant (C3S) and product(C-S-H gel) was established based on the structure parameters which were gained through testing, then the amorphous C-S-H gel was gained through molecular dynamics simulation and Monte Carlo simulation. Based on the obtained model, the admixture effects of CuO to C3S and styrol-acrylate to C-S-H gel were investigated respectively. The introduction of CuO will lower the firing temperature of C3S clinker, but will not change the overall crystal structure only leading to slight structural change. When the content of CuO is low, it enters into the crystal lattice just through solution, which never involves any chemical reaction. When the propotion of CuO is higher than3%, solid solution will happen between CuO and C3S. In this way, new phase may form. The C-S-H gel system gained through molecular dynamics simulation and Monte Carlo simulation has short-range order and long-range disorder, which belongs to amorphous structure characteristic. The final structures under different Ca/Si ratios tend to be similar. In that situation, the coordination number of atom Si and O is4, so silicon-oxygen tetrahedron is still the basic unit, and chain structure is constructed by the bridge oxygen. The styrol-acrylate, which was admixed in C-S-H gel to modify its property, dissolved preferably and enhanced the compressibility of the original system significantly, while decreased the bulk modulus and shear modulus.Based on continuous hydration medium model, the effects of some external factors, such as the quality of cement clinker and water/cement ratio, on hydration process and microstructure development were discussed finally. Assuming the cement particles are spheres which have different radius, the complicated hydration could be equivalented to a process in which the spherical particles diffuse outward. The hydration of cement and the development of microstructure could be displayed visually through effective simulation. We could observe the microstructure distribution at different hydration period (3h,6h,3d,7d,28d) of different established models, including Portland cement, low alkali cement and highalkali cement, in which the hydration products and the distribution of pore size fitted well with the realistic process. In addition, the degree of hydration and porosity increased with the increasing water/cement ratio, while the modulus of elasticity showed downward trend. We found that the moduli of elasticity are almost the same, while the water/cement ration and porosity are obviously different in all studied systems.The research of this thesis will enhance the understanding of hydration kinetic of cement and microstructure characteristic of hydration products, meanwhile it will also extend the applied range of molecular simulation. At present, the molecular simulation has not been widely used in cement-based materials yet, so the application of the technique in this area will have great potential value in future.更多还原