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Title: Densification of the interlayer spacing governs the nanomechanical properties of calcium-silicate-hydrate

Calciuam-silicate-hydrate (C-S-H) is the principal binding phase in modern concrete. Molecular simulations imply that its nanoscale stiffness is 'defect-driven', i.e., dominated by crystallographic defects such as bridging site vacancies in its silicate chains. However, experimental validation of this result is difficult due to the hierarchically porous nature of C-S-H down to nanometers. Here in this paper, we integrate high pressure X-ray diffraction and atomistic simulations to correlate the anisotropic deformation of nanocrystalline C-S-H to its atomic-scale structure, which is changed by varying the Ca-To-Si molar ratio. Contrary to the 'defect-driven' hypothesis, we clearly observe stiffening of C-S-H with increasing Ca/Si in the range 0.8 ≤ Ca/Si ≤ 1.3, despite increasing numbers of vacancies in its silicate chains. The deformation of these chains along the b-Axis occurs mainly through tilting of the Si-O-Si dihedral angle rather than shortening of the Si-O bond, and consequently there is no correlation between the incompressibilities of the a-and b-Axes and the Ca/Si. On the contrary, the intrinsic stiffness of C-S-H solid is inversely correlated with the thickness of its interlayer space. This work provides direct experimental evidence to conduct more realistic modelling of C-S-H-based cementitious material.
Authors:
 [1] ; ORCiD logo [2] ;  [3] ;  [4]
  1. Univ. of California, Berkeley, CA (United States). Dept. of Civil and Environmental Engineering
  2. Univ. of California, Berkeley, CA (United States). Dept. of Civil and Environmental Engineering; Yale Univ., New Haven, CT (United States). School of Forestry & Environmental Studies
  3. Univ. of California, Irvine, CA (United States). Dept. of Civil and Environmental Engineering
  4. Univ. of California, Berkeley, CA (United States). Dept. of Civil and Environmental Engineering; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Material Science Division
Publication Date:
Grant/Contract Number:
AC02-05CH11231; 1410557
Type:
Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 7; Journal Issue: 1; Journal ID: ISSN 2045-2322
Publisher:
Nature Publishing Group
Research Org:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 36 MATERIALS SCIENCE; Civil engineering; Colloids; Geochemistry; Mechanical properties
OSTI Identifier:
1416936