Colloidal calcium silicate hydrate (C-S-H) gel significantly contributes to cement paste's strength and durability. In this study, the coarse-grained (CG) models for packed C-S-H colloidal particles with different packing densities were established and meso-mechanically assessed via nanoindentation. Load-depth curves showed indentation hardness values (0.55, 1.16, and 2.63 GPa) for the systems with packing densities (η) of 0.50, 0.55, and 0.60, respectively. Structurally, the nano-indenter had a broader impact on low-density C-S-H (η=0.5, impact radius = 118 and 150 nm respectively at indentation depths = 50 and 100 nm) than high-density C-S-H (η=0.6, impact radius = 106 and 140 nm at the same depths). Low-density colloids were easily compressed without deforming low-depth nearby regions, while high-density colloids were squeezed laterally, causing deformation in these regions. Packed C-S-H colloids displayed two-stage stress relaxation behavior: rapid initial relaxation due to nanoindentation-induced instability, followed by slower relaxation due to C-S-H's viscous nature. Furthermore, higher loading rates caused initial unstable deformation, but better stability after stress relaxation compared to lower loading cases. However, the effect of loading rate on the impact region was negligible. These meso-level insights enhance our comprehension of the C-S-H gel properties in cement paste as well as the nanoindentation mechanics.

中文翻译：

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纳米压痕填充 CSH 胶体的细观力学：粗粒度分子动力学研究

胶体硅酸钙水合物 (CSH) 凝胶对水泥浆的强度和耐久性有显着贡献。在本研究中，建立了不同堆积密度的堆积 CSH 胶体颗粒的粗粒（CG）模型，并通过纳米压痕进行细观机械评估。载荷-深度曲线显示填充密度 (η) 分别为 0.50、0.55 和 0.60 的系统的压痕硬度值（0.55、1.16 和 2.63 GPa）。从结构上看，纳米压头对低密度CSH（η=0.5，冲击半径=118和150 nm，压痕深度=50和100 nm）比高密度CSH（η=0.6，冲击半径= 106 和 140 nm 在相同的深度）。低密度胶体很容易被压缩，而不会使附近低深度区域变形，而高密度胶体则受到横向挤压，导致这些区域变形。填充的 CSH 胶体表现出两阶段应力松弛行为：由于纳米压痕引起的不稳定性导致快速初始松弛，随后由于 CSH 的粘性性质而缓慢松弛。此外，较高的加载速率会导致初始不稳定变形，但与较低加载情况相比，应力松弛后的稳定性更好。然而，加载速率对冲击区域的影响可以忽略不计。这些介观层面的见解增强了我们对水泥浆中 CSH 凝胶特性以及纳米压痕力学的理解。