Wang Pan, Zhang Qingen, Wang Muhan, Yin Bing, Hou Dongshuai, Zhang Yue
Department of Civil Engineering, Qingdao University of Technology, Qingdao 266033, China.
Phys Chem Chem Phys. 2019 Jun 5;21(22):11892-11902. doi: 10.1039/c8cp07676f.
The transport of water and ions in the gel pores of calcium silicate hydrate (C-S-H) determines the durability of cement material. In this study, molecular dynamics was employed to investigate the capillary imbibition process of CsCl solution in the C-S-H channel. The advanced frontier of CsCl solution flow inside the C-S-H capillary shows a concave meniscus shape, which reflects the hydrophilic properties of the C-S-H substrate. Reynolds number calculations show that the transport process is laminar flow and dominated by viscous forces. The invading depth of the CsCl solution deviates from the theoretical prediction of the classic Lucas-Washburn (L-W) equation, but the modified theoretical equation, by incorporating the effect of slip length, dynamic contact angle, and effective viscosity into the L-W equation, can describe the penetration curve of the solution very well. The validity of our developed theoretical equation was confirmed by additional systems with different ion concentrations. In addition, the local structure of ions was analyzed to elucidate the effect of ion concentration on the transport process. The adsorption and accumulation of ions retard the transport process of water. With an increase in the ionic concentration, the effects of immobilization and cluster accumulation became more pronounced, further reducing the transport rate of water. This study provides fundamental insight into the transport behavior of liquid in the gel pores of cement-based material.
硅酸钙水合物（C-S-H）凝胶孔隙中水分和离子的传输决定了水泥材料的耐久性。本研究采用分子动力学方法研究了CsCl溶液在C-S-H通道中的毛细吸渗过程。C-S-H毛细管内CsCl溶液流动的前沿呈现凹液面形状，这反映了C-S-H基质的亲水性。雷诺数计算表明，传输过程为层流，且受粘性力主导。CsCl溶液的侵入深度偏离了经典卢卡斯-沃什伯恩（L-W）方程的理论预测，但通过将滑移长度、动态接触角和有效粘度的影响纳入L-W方程得到的修正理论方程，能够很好地描述溶液的渗透曲线。我们建立的理论方程的有效性通过不同离子浓度的其他体系得到了证实。此外，分析了离子的局部结构，以阐明离子浓度对传输过程的影响。离子的吸附和积累阻碍了水的传输过程。随着离子浓度的增加，固定化和团簇积累的影响变得更加明显，进一步降低了水的传输速率。本研究为水泥基材料凝胶孔隙中液体的传输行为提供了基本认识。
