基于水化硅酸钙特征的界面微结构演变模型研究

The interfacial transition zone (ITZ) between concrete matrix and aggregate is a weak phase and is critical in determining the strength and durability of concrete. ITZ is mainly composed of calcium hydroxide (CH), porosity and calcium silicate hydrate (C-S-H), the C-S-H phase which is continuously growing in ITZ plays an important role in improving the ITZ properties even the performance of cement based-material,but there are little information about characteristics and evolution of C-S-H structure in ITZ and their dynamic relationship with pores and CH which are also the main phases of ITZ, which limits the understanding of the formation mechanism of ITZ microstructure. In this study, high resolution solid-state nuclear magnetic resonance(NMR), combined with Fourier transform infrared spectroscopy, small-angle X-ray scattering(SAXS), X-ray diffraction(XRD) and thermo gravimetric analysis (TG), were used to characterize the microstructures of C-S-H in ITZ such as the average chain length (ACL), stretching vibrations of Si-O, connectivity of silicate tetrahedral, as well the CH parameters and pore parameters in ITZ, and reveal the functional relationship between these C-S-H parameters and CH, pore structural parameters in ITZ. The main objective of this study was to enrich the formation theory of ITZ and lay the theoretical foundation of the relationship between the microstructure of ITZ and mechanical properties of cement-based materials.

混凝土中骨料与浆体之间的界面是混凝土的薄弱面，会降低混凝土的强度，削弱耐久性。界面主要是由氢氧化钙(CH)、孔隙和水化硅酸钙(C-S-H)构成，界面中动态增长的C-S-H在改善界面性质乃至水泥基材料宏观性能方面发挥了重要的作用，但界面C-S-H的结构特性及演变规律鲜有报道，也很少有针对界面C-S-H、CH以及孔隙之间动态演变关系的研究。本项目采用高分辨NMR，结合FTIR、SAXS、XRD、TG等测试技术，定量表征界面C-S-H的硅氧四面体聚合状态、平均链长、Si-O振动等结构信息以及界面CH结构参数和界面孔隙特征，揭示界面C-S-H结构的演变规律，建立界面C-S-H结构参数、CH结构参数以及孔隙特征之间的函数关系，构建基于C-S-H特征的界面微结构演变模型。研究成果可丰富水泥基材料界面微结构形成演变理论，为从本质上认识界面微结构与混凝土材料宏观性能之间的关系奠定理论基础。

混凝土中骨料与浆体之间的界面是混凝土的薄弱面，会降低混凝土的强度，削弱耐久性。对于纯水泥浆体，随着水化龄期增长，大理岩骨料与水泥浆体界面区出现了Ca(OH)2的富集并形成较高的取向，且随着龄期的增长略有降低。对于不同水胶比水平，随着龄期增长，掺加粉煤灰和硅粉都改变了界面区Ca(OH)2富集状况，粉煤灰和硅粉都消耗了界面区部分Ca(OH)2。基于高分辨固体核磁共振等现代综合测试技术，提出界面区C-S-H的结构和特性。水化不同龄期，水泥浆体-大理石界面内水泥水化程度与纯水泥浆体相当，但界面样品中含有更多的二聚体C-S-H和链状C-S-H。粉煤灰和硅粉的掺入会降低界面中的C-S-H含量，尤其是降低界面中链状C-S-H的含量。掺活性掺和料界面CH晶体取向指数和平均尺寸与对应砂浆抗折、抗压强度呈线性递减关系。界面C-S-H凝胶平均链长和聚合度的提高增加了抗折和抗压强度，掺30%粉煤灰的浆体与骨料界面C-S-H凝胶聚合度对宏观力学影响较小，而纯水泥界面和掺硅粉的界面中C-S-H凝胶聚合度与宏观力学性能关系规律相似。硅粉的掺入提高了界面C-S-H凝胶聚合度，从而增强宏观力学性能。