Leaching of hydration products in cement-based materials may reduce the service life of concrete constructions, such as radioactive waste disposal containers and hydro structures. C–S–H is the most important cement hydration product, and systematic research on its nanostructures change under leaching is necessary to clarify the leaching mechanism in cement-based materials. This work aims to disclose the leaching mechanism of C–S–H with different Ca/Si ratios by immersing them in NH₄Cl solution. The chemical structure, composition and morphology of samples were investigated by XRD, TG, ICP-OES, FTIR, ²⁹Si NMR and TEM. Results show that decalcification occurs both in interlayer and intralayer of C–S–H, reducing the Ca/Si ratio to 0.67–0.70. Although initial Ca/Si ratios are different, the eventual decalcification behavior of C–S–H tends to be congruent dissolution. Additionally, Ca(OH)₂ buffers the decalcification of C–S–H. Ca leaching breaks the charge balance of C–S–H and therefore changes the chemical state of silicate tetrahedra, which increases the length of silicate chains. Meanwhile, the silicate chain in adjacent layers was linked and the amorphous silica gel was formed. Leaching coarsens the pore structure of C–S–H and transforms partial foil-like C–S–H into silica gels with flocculent morphology.

水泥基材料中水化产物的浸出可能会降低混凝土结构的使用寿命，例如放射性废物处理容器和水力结构。C-S-H是最重要的水泥水化产物，需要系统研究其在浸出下的纳米结构变化，以阐明水泥基材料的浸出机理。本工作旨在通过将 C-S-H 浸入 NH ₄ Cl 溶液中，揭示不同 Ca/Si 比的 C-S-H 的浸出机理。采用XRD 、TG、ICP-OES、FTIR、 ²⁹ Si NMR和TEM对样品的化学结构、组成和形貌进行了研究。结果表明，脱钙发生在C-S-H 的层间和层内，将 Ca/Si 比降低到 0.67-0.70。尽管初始 Ca/Si 比率不同，但 C-S-H 的最终脱钙行为往往是全等溶解。此外，Ca(OH) ₂缓冲 C-S-H 的脱钙。Ca 浸出打破了 C-S-H 的电荷平衡，因此改变了硅酸盐四面体的化学状态，从而增加了硅酸盐链的长度。同时，相邻层的硅酸盐链相连，形成无定形硅胶。浸出使 C-S-H 的孔结构变粗，并将部分箔状 C-S-H 转变为具有絮状形态的硅胶。