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      Combinatorial molecular optimization of cement hydrates

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          Abstract

          Despite its ubiquitous presence in the built environment, concrete’s molecular-level properties are only recently being explored using experimental and simulation studies. Increasing societal concerns about concrete’s environmental footprint have provided strong motivation to develop new concrete with greater specific stiffness or strength (for structures with less material). Herein, a combinatorial approach is described to optimize properties of cement hydrates. The method entails screening a computationally generated database of atomic structures of calcium-silicate-hydrate, the binding phase of concrete, against a set of three defect attributes: calcium-to-silicon ratio as compositional index and two correlation distances describing medium-range silicon-oxygen and calcium-oxygen environments. Although structural and mechanical properties correlate well with calcium-to-silicon ratio, the cross-correlation between all three defect attributes reveals an indentation modulus-to-hardness ratio extremum, analogous to identifying optimum network connectivity in glass rheology. We also comment on implications of the present findings for a novel route to optimize the nanoscale mechanical properties of cement hydrate.

          Abstract

          Concrete is a vital material in meeting present day construction demands. Here, the authors report a computational combinatorial approach to understand how molecular level characteristics influence the mechanical properties of cement hydrates, via screening against distinct defect types.

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          Most cited references 61

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          Topology of covalent non-crystalline solids I: Short-range order in chalcogenide alloys

           J.C. Phillips (1979)
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            Composition and density of nanoscale calcium-silicate-hydrate in cement.

            Although Portland cement concrete is the world's most widely used manufactured material, basic questions persist regarding its internal structure and water content, and their effect on concrete behaviour. Here, for the first time without recourse to drying methods, we measure the composition and solid density of the principal binding reaction product of cement hydration, calcium-silicate-hydrate (C-S-H) gel, one of the most complex of all gels. We also quantify a nanoscale calcium hydroxide phase that coexists with C-S-H gel. By combining small-angle neutron and X-ray scattering data, and by exploiting the hydrogen/deuterium neutron isotope effect both in water and methanol, we determine the mean formula and mass density of the nanoscale C-S-H gel particles in hydrating cement. We show that the formula, (CaO)1.7(SiO2)(H2O)1.80, and density, 2.604 Mg m(-3), differ from previous values for C-S-H gel, associated with specific drying conditions. Whereas previous studies have classified water within C-S-H gel by how tightly it is bound, in this study we classify water by its location-with implications for defining the chemically active (C-S-H) surface area within cement, and for predicting concrete properties.
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              Constraint theory, vector percolation and glass formation

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                Author and article information

                Journal
                Nat Commun
                Nat Commun
                Nature Communications
                Nature Pub. Group
                2041-1723
                24 September 2014
                : 5
                Affiliations
                [1 ]Department of Civil and Environmental Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USA
                [2 ]<MSE>2 MIT-CNRS Joint Laboratory , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USA
                [3 ]Department of Material Science and Engineering , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USA
                [4 ]Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue , Cambridge, Massachusetts 02139-4307, USA
                [5 ]Centre Interdisciplinaire des Nanosciences de Marseille, CNRS and AIX-Marseille Université, Campus de Luminy , 13288 Marseille, Cedex 09, France
                [6 ]Department of Nuclear Science and Engineering, Massachusetts Institute of Technology , 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
                Author notes
                [*]

                Present address: Department of Civil and Environmental Engineering, University of California, Los Angeles, California 90095, USA

                [†]

                Present address: Bayer MaterialScience LLC, 100 Bayer Rd, Pittsburgh, Pennsylvania 15205, USA

                [‡]

                Present address: Department of Civil and Environmental Engineering and Department of Material Science and NanoEngineering, Rice University, 6100 Main Street MS-519, Houston, Texas 77005, USA

                [§]

                Present address: EyeNetra, Inc, 35 Medford St., Somerville, Massachusetts, USA

                Article
                ncomms5960
                10.1038/ncomms5960
                4200522
                25248305
                Copyright © 2014, Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.

                This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/4.0/

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