Silicon-29 and oxygen-17 nuclear magnetic resonance investigation of the structure of calcium-silicate-hydrate
Cong, Xiandong
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https://hdl.handle.net/2142/22613
Description
Title
Silicon-29 and oxygen-17 nuclear magnetic resonance investigation of the structure of calcium-silicate-hydrate
Author(s)
Cong, Xiandong
Issue Date
1994
Doctoral Committee Chair(s)
Kirkpatrick, R. James
Department of Study
Geology
Discipline
Geology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Geology
Engineering, Civil
Engineering, Materials Science
Language
eng
Abstract
This thesis investigates the structure of calcium-silicate-hydrate (C-S-H), a major hydration product of Portland cement, using primarily $\sp{29}$Si and $\sp{17}$O MAS and $\sp1$H-$\sp{29}$Si CPMAS NMR, XRD, chemical and thermal analysis. It presents a comprehensive defect-tobermorite structural model for C-S-H.
C-S-H gels with C/S ratios ranging from 0.4 to 1.85 have been synthesized by hydration of highly reactive $\beta$-$C\sb2S,$ reaction of fumed silica and CaO in aqueous solution and reaction of highly reactive $\beta$-$C\sb2S$ and fumed silica. Phase-pure C-S-H has C/S ratios between 0.6-1.54. The main findings include the following: (1) C-S-H shows continuity and diversity in both composition and structure and forms a continuous series. (2) At least six O-sites have been identified, two NBO's, BO, Ca-OH, Si-OH and $H\sb2O.$ The compositional variation of the relative intensities for different sites measured by $\sp{17}$O NMR is consistent with that calculated from $\sp{29}$Si NMR. (3) There is significant proton motion at room temperature at frequencies of 10$\sp4$-10$\sp5$ Hz. (4) Silicate chain length distribution of the C-S-H samples with C/S $>$ 1 is not unimodal. There are probably many dimers and relatively long chains in the structure, but few chains with intermediate length. An ideal formula for C-S-H with a C/S ratio of 1.5 is: $Ca\sb{4.5}\lbrack Si\sb3O\sb8(OH)\rbrack(OH)\sb4\cdot nH\sb2O.$ All the evidence indicates that the structure of C-S-H is more similar to that of 1.4-nm tobermorite than to jennite. A defect-tobermorite structural model is proposed for C-S-H in which individual layers have the basic structure of 1.4-nm tobermorite but are more disordered. Stacking disorder in adjacent layers and disorder within individual layers may both contribute to the local and long range disorder and thus to the diversity of C-S-H.
Structures of some potential crystalline model compounds including 1.1-nm tobermorite, 1.4-nm tobermorite, jennite, calciochondrodite, xonotlite and hillebrandite, have also been studied. The $\sp{17}$O and most of the $\sp1$H-$\sp{29}$Si CPMAS results are the first reported for these phases. The two tobermorites are structurally similar and jennite contains long, single silicate chains.
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