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Title: Non-ideal solid solution aqueous solution modeling of synthetic calcium silicate hydrate

Abstract

New data relevant to calcium silicate hydrate (C-S-H) gels prepared at room temperature have been obtained over a time period of up to 112 weeks. X-ray diffraction (XRD) indicates equilibrium was attained after 64 weeks. Coupled with fourier transform infrared (FT-IR) spectroscopy, a phase change in C-S-H gel at Ca/Si {approx} 1.0 was identified and the occurrence of portlandite as a distinct phase for Ca/Si > 1.64. The incongruent dissolution of C-S-H gel was modeled as a non-ideal solid solution aqueous solution (SSAS) between the end-member components CaH{sub 2}SiO{sub 4} (CSH) and Ca(OH){sub 2} (CH) using equations defining the solidus and solutus curves on a Lippmann phase diagram. Despite being semi-empirical, the model provides a reasonable and consistent fit to the solubility data and can therefore be used to describe the incongruent dissolution of C-S-H gels with compositions Ca/Si {>=} 1.0.

Authors:
 [1];  [2];  [3];  [4]
  1. Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol, BS8 1RJ (United Kingdom). E-mail: c.walker@nhm.ac.uk
  2. Quintessa Limited, Dalton House, Newtown Road, Henley-on-Thames, RG9 1HG (United Kingdom)
  3. Department of Materials, Imperial College, South Kensington, London, SW7 2AZ (United Kingdom)
  4. Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen's Road, Bristol, BS8 1RJ (United Kingdom)
Publication Date:
OSTI Identifier:
20995375
Resource Type:
Journal Article
Resource Relation:
Journal Name: Cement and Concrete Research; Journal Volume: 37; Journal Issue: 4; Other Information: DOI: 10.1016/j.cemconres.2006.12.002; PII: S0008-8846(06)00314-0; Copyright (c) 2006 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; AQUEOUS SOLUTIONS; CALCIUM HYDROXIDES; CALCIUM SILICATES; DISSOLUTION; EQUILIBRIUM; FOURIER TRANSFORMATION; GELS; HYDRATES; INFRARED SPECTRA; PHASE DIAGRAMS; SIMULATION; SOLID SOLUTIONS; SOLUBILITY; TEMPERATURE RANGE 0273-0400 K; X-RAY DIFFRACTION

Citation Formats

Walker, Colin S., Savage, David, Tyrer, Mark, and Ragnarsdottir, K. Vala. Non-ideal solid solution aqueous solution modeling of synthetic calcium silicate hydrate. United States: N. p., 2007. Web. doi:10.1016/j.cemconres.2006.12.002.
Walker, Colin S., Savage, David, Tyrer, Mark, & Ragnarsdottir, K. Vala. Non-ideal solid solution aqueous solution modeling of synthetic calcium silicate hydrate. United States. doi:10.1016/j.cemconres.2006.12.002.
Walker, Colin S., Savage, David, Tyrer, Mark, and Ragnarsdottir, K. Vala. Sun . "Non-ideal solid solution aqueous solution modeling of synthetic calcium silicate hydrate". United States. doi:10.1016/j.cemconres.2006.12.002.
@article{osti_20995375,
title = {Non-ideal solid solution aqueous solution modeling of synthetic calcium silicate hydrate},
author = {Walker, Colin S. and Savage, David and Tyrer, Mark and Ragnarsdottir, K. Vala},
abstractNote = {New data relevant to calcium silicate hydrate (C-S-H) gels prepared at room temperature have been obtained over a time period of up to 112 weeks. X-ray diffraction (XRD) indicates equilibrium was attained after 64 weeks. Coupled with fourier transform infrared (FT-IR) spectroscopy, a phase change in C-S-H gel at Ca/Si {approx} 1.0 was identified and the occurrence of portlandite as a distinct phase for Ca/Si > 1.64. The incongruent dissolution of C-S-H gel was modeled as a non-ideal solid solution aqueous solution (SSAS) between the end-member components CaH{sub 2}SiO{sub 4} (CSH) and Ca(OH){sub 2} (CH) using equations defining the solidus and solutus curves on a Lippmann phase diagram. Despite being semi-empirical, the model provides a reasonable and consistent fit to the solubility data and can therefore be used to describe the incongruent dissolution of C-S-H gels with compositions Ca/Si {>=} 1.0.},
doi = {10.1016/j.cemconres.2006.12.002},
journal = {Cement and Concrete Research},
number = 4,
volume = 37,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • Calcium–silicate–hydrate (C–S–H) gel is the main binder component in hydrated ordinary Portland cement (OPC) paste, and is known to play a crucial role in the carbonation of cementitious materials, especially for more sustainable alternatives containing supplementary cementitious materials. However, the exact atomic structural changes that occur during carbonation of C–S–H gel remain unknown. Here, we investigate the local atomic structural changes that occur during carbonation of a synthetic calcium–silicate–hydrate gel exposed to pure CO₂ vapour, using in situ X-ray total scattering measurements and subsequent pair distribution function (PDF) analysis. By analysing both the reciprocal and real-space scattering data as themore » C–S–H carbonation reaction progresses, all phases present during the reaction (crystalline and non-crystalline) have been identified and quantified, with the results revealing the emergence of several polymorphs of crystalline calcium carbonate (vaterite and calcite) in addition to the decalcified C–S–H gel. Furthermore, the results point toward residual calcium being present in the amorphous decalcified gel, potentially in the form of an amorphous calcium carbonate phase. As a result of the quantification process, the reaction kinetics for the evolution of the individual phases have been obtained, revealing new information on the rate of growth/dissolution for each phase associated with C–S–H gel carbonation. Moreover, the investigation reveals that the use of real space diffraction data in the form of PDFs enables more accurate determination of the phases that develop during complex reaction processes such as C–S–H gel carbonation in comparison to the conventional reciprocal space Rietveld analysis approach.« less
  • In this work, the relationship between the composition of pore solution in alkali-activated slag cement (AAS) pastes activated with different alkaline activator, and the composition and structure of the main reaction products, has been studied. Pore solution was extracted from hardened AAS pastes. The analysis of the liquids was performed through different techniques: Na, Mg and Al by atomic absorption (AA), Ca ions by ionic chromatography (IC) and Si by colorimetry; pH was also determined. The solid phases were analysed by XRD, FTIR, solid-state {sup 29}Si and {sup 27}Al NMR and BSE/EDX. The most significant changes in the ionic compositionmore » of the pore solution of the AAS pastes activated with waterglass take place between 3 and 24 h of reaction. These changes are due to the decrease of the Na content and mainly to the Si content. Results of {sup 29}Si MAS NMR and FTIR confirm that the activation process takes place with more intensity after 3 h (although at this age, Q{sup 2} units already exist). The pore solution of the AAS pastes activated with NaOH shows a different evolution to this of pastes activated with waterglass. The decrease of Na and Si contents progresses with time. The nature of the alkaline activator influences the structure and composition of the calcium silicate hydrate formed as a consequence of the alkaline activation of the slag. The characteristic of calcium silicate hydrate in AAS pastes activated with waterglass is characterised by a low structural order with a low Ca/Si ratio. Besides, in this paste, Q{sup 3} units are detected. The calcium silicate hydrate formed in the pastes activated with NaOH has a higher structural order (higher crystallinity) and contains more Al in its structure and a higher Ca/Si ratio than those obtained with waterglass.« less
  • This study assesses the quantitative effects of incorporating high-volume fly ash (HVFA) into tricalcium silicate (C 3S) paste on the hydration, degree of silicate polymerization, and Al substitution for Si in calcium silicate hydrate (C–S–H). Thermogravimetric analysis and isothermal conduction calorimetry showed that, although the induction period of C 3S hydration was significantly extended, the degree of hydration of C 3S after the deceleration period increased due to HVFA incorporation. Synchrotron-sourced soft X-ray spectromicroscopy further showed that most of the C 3S in the C 3S-HVFA paste was fully hydrated after 28 days of hydration, while that in the puremore » C 3S paste was not. The chemical shifts of the Si K edge peaks in the near-edge X-ray fine structure of C–S–H in the C 3S-HVFA paste directly indicate that Al substitutes for Si in C–S–H and that the additional silicate provided by the HVFA induces an enhanced degree of silicate polymerization. This new spectromicroscopic approach, supplemented with 27Al and 29Si magic-angle spinning nuclear magnetic resonance spectroscopy and transmission electron microscopy, turned out to be a powerful characterization tool for studying a local atomic binding structure of C–S–H in C 3S-HVFA system and presented results consistent with previous literature.« less
  • Some studies on the fluoride adsorbancy of synthetic calcium monohydrogen phospchnte and synthetic sintered and unsintered zirconium silicate and beryllium silicate were made. Ten ppm of fluoride was passed at about 0.3 ml/ min through chromatographic tubes packed with the material under study together with diatomaceous earth, and the conceutration of the fluoride in the effluent solution determined. The materials which were sintered with glass adsorbed very slight amouris of fluoride. Calcium phosphate and unsintered beryllium silicate adsorbed about half of the fluoride from 50 ml of 10 ppm fluoride solution. Unsintered zirconium silicate adsorbed all detectable fluoride from suchmore » a solution. One gram of zirconium silicate adsorbed as much as 5 mg of fluoride from solution. Passing O.1 N sodium carbonate through the zirconium silicate columns caused adsorbed fluoride to be released; however, the extent of fiuoride recovery by this method varied unpredictably between 30 and 100%. (auth)« less