Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS-Université de Bourgogne, 9 Avenue Savary, BP 47 870, F-21078 Dijon Cedex, France.
Inorg Chem. 2012 Feb 6;51(3):1827-36. doi: 10.1021/ic202124x. Epub 2012 Jan 25.
Calcium silicate hydrate (C-S-H) is the main constituent of hydrated cement paste and determines its cohesive properties. Because of the environmental impact of cement industry, it is more and more common to replace a part of the clinker in cement by secondary cementitious materials (SCMs). These SCMs are generally alumina-rich and as a consequence some aluminum is incorporated into the C-S-H. This may have consequences on the cohesion and durability of the material, and it is thus of importance to know the amount and the location of Al in C-S-H and what the parameters are that control these features. The present paper reports the (29)Si and (27)Al MAS NMR analyses of well-characterized C-A-S-H samples (C-S-H containing Al). These samples were synthesized using an original procedure that successfully leads to pure C-A-S-H of controlled compositions in equilibrium with well-characterized solutions. The (27)Al MAS NMR spectra were quantitatively interpreted assuming a tobermorite-like structure for C-A-S-H to determine the aluminum location in this structure. For this purpose, an in-house written software was used which allows decomposing several spectra simultaneously using the same constrained spectral parameters for each resonance but with variable intensities. The hypothesis on the aluminum location in the C-A-S-H structure determines the proportion of each silicon site. Therefore, from the (27)Al NMR quantitative results and the chemical composition of each sample, the intensity of each resonance line in the (29)Si spectra was set. The agreement between the experimental and calculated (29)Si MAS NMR spectra corroborates the assumed C-A-S-H structure and the proposed Al incorporation mechanism. The consistency between the results obtained for all compositions provides another means to assess the assumptions on the C-A-S-H structure. It is found that Al substitutes Si mainly in bridging positions and moderately in pairing positions in some conditions. Al in pairing site is observed only for Ca/(Si+Al) ratios greater than 0.95 (equivalent to 4 mmol.L(-1) of calcium hydroxide). Finally, the results suggest that penta and hexa-coordinated aluminum are adsorbed on the sides of the C-A-S-H particles.
硅酸钙水合物（C-S-H）是水合水泥浆的主要成分，决定了其粘性特性。由于水泥工业对环境的影响，越来越多的情况下，水泥中的熟料部分被二次胶凝材料（SCM）所取代。这些 SCM 通常富含氧化铝，因此一些铝被掺入 C-S-H 中。这可能会对材料的粘性和耐久性产生影响，因此了解 C-S-H 中铝的含量和位置以及控制这些特性的参数非常重要。本文报道了经过充分表征的 C-A-S-H 样品（含铝的 C-S-H）的（29）Si 和（27）Al MAS NMR 分析。这些样品是使用一种原始程序合成的，该程序成功地合成了具有受控组成的纯 C-A-S-H，并与经过充分表征的溶液达到平衡。（27）Al MAS NMR 谱图是在假设 C-A-S-H 具有托贝莫来石结构的情况下进行定量解释的，以确定该结构中铝的位置。为此，使用了一个内部编写的软件，该软件允许使用相同的约束谱参数对每个共振进行同时分解，但强度可变。在 C-A-S-H 结构中铝的位置假设决定了每个硅位的比例。因此，从（27）Al NMR 定量结果和每个样品的化学组成出发，确定了（29）Si 谱中每个共振线的强度。实验和计算（29）Si MAS NMR 谱之间的一致性证实了假设的 C-A-S-H 结构和提出的 Al 掺入机制。所有组成的结果之间的一致性提供了另一种评估 C-A-S-H 结构假设的方法。结果表明，在某些条件下，铝主要取代桥位的硅，适度取代配位的硅。仅在 Ca/（Si+Al）比值大于 0.95（相当于 4 mmol·L（-1）的氢氧化钙）时，才观察到配位位的铝。最后，结果表明五配位和六配位的铝被吸附在 C-A-S-H 颗粒的侧面。
