Li Xiaopeng, Zhang Hongping, Zhan Haifei, Tang Youhong
School of Materials and Chemistry, Southwest University of Science and Technology, Mianyang 621010, China.
School of Mechanical Engineering, Institute for Advanced Study, Chengdu University, Chengdu 610106, China.
Nanomaterials (Basel). 2023 Aug 8;13(16):2279. doi: 10.3390/nano13162279.
As calcium silicate hydrate (C-S-H) is the main binding phase in concrete, understanding the doping behavior of impurity elements in it is important for optimizing the structure of cementitious materials. However, most of the current studies focus on cement clinker, and the doping mechanism of impurity elements in hydrated calcium silicate is not yet fully understood. The hydrated calcium silicate component is complex, and its structure is very similar to that of the tobermorite mineral family. In this study, the effects of three different dopants (Mg, Sr and Ba) on a representing structure of C-S-H-tobermorite-was systematically explored using densify functional theory (DFT) calculations. The calculations show that Mg doping leads to a decrease in lattice volume and causes obvious structure and coordination changes of magnesium-oxygen polyhedra. This may be the reason why high formation energy is required for the Mg-doped tobermorite. Meanwhile, doping only increases the volume of the Sr- and Ba-centered oxygen polyhedra. Specifically, the Mg-doped structure exhibits higher chemical stability and shorter interatomic bonding. In addition, although Mg doping distorts the structure, the stronger chemical bonding between Mg-O atoms also improves the compressive (1.99% on average) and shear resistance (2.74% on average) of tobermorillonite according to the elastic modulus and has less effect on the anisotropy of the Young's modulus. Our results suggest that Mg doping is a promising strategy for the optimized structural design of C-S-H.
由于水化硅酸钙（C-S-H）是混凝土中的主要粘结相，了解其中杂质元素的掺杂行为对于优化胶凝材料的结构至关重要。然而，目前大多数研究集中在水泥熟料上，水化硅酸钙中杂质元素的掺杂机制尚未完全了解。水化硅酸钙成分复杂，其结构与雪硅钙石矿物家族非常相似。在本研究中，使用密度泛函理论（DFT）计算系统地探索了三种不同掺杂剂（Mg、Sr和Ba）对C-S-H代表性结构——雪硅钙石的影响。计算结果表明，Mg掺杂导致晶格体积减小，并引起镁氧多面体明显的结构和配位变化。这可能是Mg掺杂雪硅钙石需要高形成能的原因。同时，掺杂仅增加了以Sr和Ba为中心的氧多面体的体积。具体而言，Mg掺杂结构表现出更高的化学稳定性和更短的原子间键长。此外，虽然Mg掺杂使结构发生畸变，但根据弹性模量，Mg-O原子之间更强的化学键也提高了雪硅钙石的抗压强度（平均约1.99%）和抗剪强度（平均约2.74%），并且对杨氏模量的各向异性影响较小。我们的结果表明，Mg掺杂是C-S-H优化结构设计的一种有前景的策略。
