Knowing the chloride ingress rate is crucial in predicting the service life of reinforced concrete in chlorine environment. While empirical diffusion model is available, fundamental knowledge of Cl diffusion in calcium silicate hydrate (C-S-H) is largely lacking as it is experimentally challenging to prepare a bulk pure C-S-H. In this study, synthesized C-S-H powder was compacted to form pellets of controlled pore structure and Ca/Si. Effective diffusion coefficients of Cl in these C-S-H matrixes were measured using steady-state natural diffusion and electric-migration tests, as a function of Ca/Si and porosity. Increased pore tortuosity significantly reduced diffusivity even when porosity remains nearly unchanged. The influence of pore-solution pH to Cl diffusion is distinct between natural-diffusion and electric-migration. Our data provides the first direct measure of Cl diffusion coefficient in pure C-S-H matrix, and new insights into the surface effect for diffusion in extremely small pores.

中文翻译：

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纯 CSH 多孔空间中的固有氯离子传输行为

了解氯离子侵入率对于预测氯环境中钢筋混凝土的使用寿命至关重要。虽然经验扩散模型可用，但很大程度上缺乏 Cl 在硅酸钙水合物 (CSH) 中扩散的基础知识，因为制备大量纯 CSH 在实验上具有挑战性。在本研究中，将合成的 CSH 粉末压实，形成具有受控孔隙结构和 Ca/Si 的颗粒。使用稳态自然扩散和电迁移测试测量了这些 CSH 基质中 Cl 的有效扩散系数，作为 Ca/Si 和孔隙率的函数。即使孔隙率几乎保持不变，孔隙扭曲度的增加也会显着降低扩散率。自然扩散和电迁移之间，孔隙溶液 pH 值对 Cl 扩散的影响是不同的。我们的数据首次直接测量了纯 CSH 基质中的 Cl 扩散系数，并为极小孔隙中扩散的表面效应提供了新的见解。