早在2000多年前，古罗马帝国便开始用混凝土浇筑大型建筑物。然而时至今日，研究人员已经分析了许多材料的分子结构，但不可思议的是，应用极为广泛并排放出大量温室气体的混凝土化合物的分子结构却始终没有破译。 
        现在MIT的团队对混凝土展开了研究，研究小组发现混凝土中的钙-二氧化硅水合物并不是真正的晶体，它是某种晶体结构和非晶体结构的混合。研究论文(开放获取)发表在PNAS上。论文作者之一的民用和环境工程部教授Franz-Josef Ulm称，在混凝土的纳米结构就像是杂货店金字塔形状的水果。水能削弱一些材料的强度，但却能增加混凝土水合物的强度，这要拜其混杂的结构所赐。通过了解分子结构，研究人员也能开发出新型的能满足不同需求的混凝土材料。

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A realistic molecular model of cement hydrates

1. Roland J.-M. Pellenq^a,^b,
2. Akihiro Kushima^c,
3. Rouzbeh Shahsavari^b,
4. Krystyn J. Van Vliet^d,
5. Markus J. Buehler^b,
6. Sidney Yip^c,^d and
7. Franz-Josef Ulm^b,¹

+ Author Affiliations

1. ^aCentre Interdisciplinaire des Nanosciences de Marseille, Centre National de la Recherche Scientifique and Marseille Université, Campus de Luminy, Marseille, 13288 Cedex 09, France;
2. Departments of ^bCivil and Environmental Engineering,
3. ^cNuclear Science and Engineering, and
4. ^dMaterials Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139

1. Edited by Zdeněk P. Ba?ant, Northwestern University, Evanston, IL, and approved July 21, 2009 (received for review February 27, 2009)

Abstract

Despite decades of studies of calcium-silicate-hydrate (C-S-H), the structurally complex binder phase of concrete, the interplay between chemical composition and density remains essentially unexplored. Together these characteristics of C-S-H define and modulate the physical and mechanical properties of this “liquid stone” gel phase. With the recent determination of the calcium/silicon (C/S = 1.7) ratio and the density of the C-S-H particle (2.6 g/cm³) by neutron scattering measurements, there is new urgency to the challenge of explaining these essential properties. Here we propose a molecular model of C-S-H based on a bottom-up atomistic simulation approach that considers only the chemical specificity of the system as the overriding constraint. By allowing for short silica chains distributed as monomers, dimers, and pentamers, this C-S-H archetype of a molecular description of interacting CaO, SiO₂, and H₂O units provides not only realistic values of the C/S ratio and the density computed by grand canonical Monte Carlo simulation of water adsorption at 300 K. The model, with a chemical composition of (CaO)_1.65(SiO₂)(H₂O)_1.75, also predicts other essential structural features and fundamental physical properties amenable to experimental validation, which suggest that the C-S-H gel structure includes both glass-like short-range order and crystalline features of the mineral tobermorite. Additionally, we probe the mechanical stiffness, strength, and hydrolytic shear response of our molecular model, as compared to experimentally measured properties of C-S-H. The latter results illustrate the prospect of treating cement on equal footing with metals and ceramics in the current application of mechanism-based models and multiscale simulations to study inelastic deformation and cracking.