Engineering the bonding scheme in C-S-H: The iono-covalent framework
Engineering the bonding scheme in C-S-H: The iono-covalent framework
复制标题
DOI：
10.1016/j.cemconres.2007.09.026
复制
发表时间：
2008-02-01
影响因子：
11.4
通讯作者：
van Damme, H.
中科院分区：
文献类型：
--
作者：
Pellenq, R. J. -M.;Lequeux, N.;van Damme, H.
在最近的分子模拟和实验研究的基础上，我们讨论了通过在分子水平上修改水合物中的键合方案来调整胶凝材料力学性能的两种可能策略。我们重点讨论硅酸钙水合物（C-S-H）。第一个策略是基于加强各个 C-S-H 片层之间或其微晶之间作用的内聚力网络。从头算、分子动力学和能量最小化技术进行的原子尺度模拟表明，由强局域钙离子和水分子分隔开的各个 C-S-H 层或 C-S-H 层堆叠之间的离子共价力比由纳米或多纳米厚的流动水分子和离子层分隔的 C-S-H 表面之间作用的离子相关力大几个数量级。源自该离子-共价键合方案的弹性性能与通过超声波或统计（“网格”）纳米压痕技术获得的实验值非常一致。接下来的 C-S-H 的概念图是晶体半连续体的概念图，具有彼此离子共价键合的致密域（“微晶”或“颗粒”），也可能纠缠在一起，并且只要中尺度孔隙由于波动的静电力而在相对较弱的吸引力应力场中被水饱和，就可以嵌入。根据微晶的尺寸、长宽比和乱层顺序，以及间隙溶液的组成，可以修改每个贡献的相对重要性。这为更好地控制特性（例如早期或长期力量发展）提供了基础。在这方面，粘土矿物的微观结构-性能关系提供了有趣的线索，指出了粘结连续性而不是粘结强度的重要性。调整水泥体系机械性能的第二种策略（类似于仿生方法）是通过在矿物片晶上接枝有机部分来杂化水合物。这可以通过有机硅烷前体混合物的受控水解或通过在硅烷化聚合物溶液中进行无水硅酸盐的水合来实现。结果可能是材料具有更高的断裂能和更大的失效应变。 (C) 2007 Elsevier Ltd. 保留所有权利。
On the basis of recent molecular simulation and experimental studies, we discuss two possible strategies for tuning the mechanical properties of cememitious materials by modifying the bonding scheme in the hydrates at molecular level. We focus the discussion on the calcium silicate hydrates (C-S-H). A first strategy would be based on the strengthening of the network of cohesion forces acting between the individual C-S-H lamellae or between their crystallites. Atomic scale simulations by ab initio, molecular dynamics and energy minimization techniques show that the iono-covalent forces between individual C-S-H layers or C-S-H layer stacks, separated by strongly localized calcium ions and water molecules, are orders of magnitude larger than the ionic correlation forces acting between C-S-H surfaces separated by nm- or multi-nm-thick layers of mobile water molecules and ions. The elastic properties derived from this iono-covalent bonding scheme are in good agreement with experimental values obtained by ultrasonic or statistical ("grid") nanoindentation techniques. The concept picture for C-S-H which follows is that of a crystalline semi-continuum, with dense domains ("crystallites" or "particles") iono-covalently bonded to each other, possibly entangled also, and embedded as long as the mesoscale porosity is water-saturated in a relatively weak attractive stress field due to fluctuating electrostatic forces. Depending on the size, the aspect ratio, and the turbostratic order of the crystallites, and also the composition of the interstitial solution, the relative importance of each contribution could be modified. This provides the basis for a better control of properties such as early age or long term strength development for instance. In this respect, the microstructure-properties relationships in clay minerals provide interesting leads, pointing to the importance of bonding continuity rather than bond strength.A second strategy to tune the mechanical properties of cement systems, akin to a biomimetic approach, is to hybridize the hydrates by grafting organic moieties on the mineral lamellac. This can be achieved by controlled hydrolysis of organo-silane precursor mixtures or by performing the hydration of the anhydrous silicates in silanized polymer solutions. The outcome may be materials with improved fracture energy and larger strain at failure. (C) 2007 Elsevier Ltd. All rights reserved.