Abstract Owing to the hierarchical pore structures of cement paste, varying gas diffusion mechanisms, i.e. surface, Knudsen and molecular diffusion, coexist. However, their combined effects have not been fully investigated. To this end, a multi-scale model which considers the combined effects is developed to simulate and analyse the effective gas diffusivity in dry cement paste. The multi-scale structures of cement paste using representative volume elements are reconstructed, capturing the structural characteristics at each scale. Afterwards, based on classical adsorption theory, random walk method and lattice Boltzmann method, the gas diffusivity at each scale is predicted and analysed. The results indicate that surface diffusion plays an important role in the gas diffusion in C-S-H, while the main diffusion regime in C-S-H gradually becomes Knudsen diffusion as the porosity increases. The surface and Knudsen diffusion cannot be ignored or simplified as molecular diffusion in the prediction of gas diffusivity in cement paste.

中文翻译：

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模拟干水泥浆体中有效气体扩散率的多尺度框架：表面、克努森和分子扩散的综合影响

摘要 由于水泥浆体的分级孔隙结构，不同的气体扩散机制，即表面扩散、克努森扩散和分子扩散并存。然而，它们的综合影响尚未得到充分研究。为此，开发了一个考虑组合效应的多尺度模型来模拟和分析干水泥浆体中的有效气体扩散率。使用代表性体积元素重建水泥浆的多尺度结构，捕捉每个尺度的结构特征。随后，基于经典吸附理论、随机游走法和格子玻尔兹曼法，对各尺度的气体扩散率进行了预测和分析。结果表明，表面扩散在 CSH 中的气体扩散中起重要作用，而随着孔隙度的增加，CSH 中的主要扩散方式逐渐变为 Knudsen 扩散。在预测水泥浆体中的气体扩散率时，表面和克努森扩散不能被忽略或简化为分子扩散。