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Title: The nanogranular nature of c-s-h
Authors: Constantinides, Georgios 
Ulm, Franz Josef 
Keywords: Granular materials
Statistical methods
Nanostructured materials
Issue Date: 2007
Publisher: Elsevier
Source: Journal of the Mechanics and Physics of Solids,2007, Volume 55, Issue 1,Pages 64-90
Abstract: Despite its ubiquitous presence as binding phase in all cementitious materials, the mechanical behavior of calcium-silicate-hydrates (C-S-H) is still an enigma that has deceived many decoding attempts from experimental and theoretical sides. In this paper, we propose and validate a new technique and experimental protocol to rationally assess the nanomechanical behavior of C-S-H based on a statistical analysis of hundreds of nanoindentation tests. By means of this grid indentation technique we identify in situ two structurally distinct but compositionally similar C-S-H phases heretofore hypothesized to exist as low density (LD) C-S-H and high density (HD) C-S-H, or outer and inner products. The main finding of this paper is that both phases exhibit a unique nanogranular behavior which is driven by particle-to-particle contact forces rather than by mineral properties. We argue that this nanomechanical blueprint of material invariant behavior of C-S-H is a consequence of the hydration reactions during which precipitating C-S-H nanoparticles percolate generating contact surfaces. As hydration proceeds, these nanoparticles pack closer to center on-average around two characteristic limit packing densities, the random packing limit (η = 64 %) and the ordered face-centered cubic (fcc) or hexagonal close-packed (hcp) packing limit (η = 74 %), forming a characteristic LD C-S-H and HD C-S-H phase.
ISSN: 0022-5096
DOI: 10.1016/j.jmps.2006.06.003
Rights: © Elsevier Ltd. All rights reserved.
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