Concrete gains its strength from the precipitation of a calcium–alumino–silicate–hydrate (C–A–S–H) colloidal gel, which acts as its binding phase. However, despite concrete’s ubiquity in the building environment, the atomic-scale mechanism of C–A–S–H precipitation is still unclear. Here, we use reactive molecular dynamics simulations to model the early-age precipitation of a C–A–S–H gel. We find that, upon gelation, silicate and aluminate precursors condensate and polymerize to form an aluminosilicate gel network. Notably, we demonstrate that the gelation reaction is driven by the existence of a mismatch of atomic-level internal stress between Si and Al polytopes, which are initially experiencing some local tension and compression, respectively. The polymerization of Si and Al polytopes enables the release of these competitive stresses.

中文翻译：

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钙铝硅酸盐水合物凝胶的沉淀：内应力的作用。

混凝土是通过钙-铝-硅酸盐-水合物（C–A–S–H）胶体凝胶的沉淀而获得强度的，该胶体是其粘结相。但是，尽管混凝土在建筑环境中无处不在，但C–A–S–H沉淀的原子尺度机理仍然不清楚。在这里，我们使用反应性分子动力学模拟来模拟C–A–S–H凝胶的早期沉淀。我们发现，在凝胶化时，硅酸盐和铝酸盐前体会冷凝并聚合形成铝硅酸盐凝胶网络。值得注意的是，我们证明了胶凝反应是由Si和Al多原子簇之间原子级内应力不匹配的存在驱动的，Si和Al多原子簇最初分别经历了一些局部张力和压缩。Si和Al多表位的聚合能够释放这些竞争压力。