Hostname: page-component-cd9895bd7-q99xh Total loading time: 0 Render date: 2024-12-27T10:27:06.798Z Has data issue: false hasContentIssue false
  • English
  • Français

Calcium silicate hydrate (C-S-H) gel dissolution and pH buffering in a cementitious near field

Published online by Cambridge University Press:  05 July 2018

G. M. N. Baston ,
A. P. Clacher ,
T. G. Heath ,
F. M. I. Hunter ,
V. Smith  and
S. W. Swanton
G. M. N. Baston
Affiliation:
AMEC, Building 150, Thomson Avenue, Harwell, Didcot, Oxfordshire, OX11 0QB
A. P. Clacher
Affiliation:
AMEC, Building 150, Thomson Avenue, Harwell, Didcot, Oxfordshire, OX11 0QB
T. G. Heath*
Affiliation:
AMEC, Building 150, Thomson Avenue, Harwell, Didcot, Oxfordshire, OX11 0QB
F. M. I. Hunter
Affiliation:
AMEC, Building 150, Thomson Avenue, Harwell, Didcot, Oxfordshire, OX11 0QB
V. Smith
Affiliation:
AMEC, Building 150, Thomson Avenue, Harwell, Didcot, Oxfordshire, OX11 0QB
S. W. Swanton
Affiliation:
AMEC, Building 150, Thomson Avenue, Harwell, Didcot, Oxfordshire, OX11 0QB
*
*E-mail: [email protected]
Rights & Permissions [Opens in a new window]

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

A cementitious backfill has been proposed in many geological disposal concepts for intermediate-level waste and low-level waste in the UK and elsewhere. In this paper, the main features of the chemical evolution of backfill and the associated changes in the near-field pH are illustratedwith results from recent work. For example, interaction of the groundwater with calcium silicate hydrate (C-S-H) phases in a backfill is expected to play an important role in the long-term pH-buffering behaviour. Existing experimental data for the dissolution of C-S-H gels are compared withrecent experimental results from leach tests on gels of a lower calcium to silicon ratio (C/S) to provide a consistent set of data across the full C/S range. The results confirm that a congruent dissolution point around C/S = 0.8 is approached by leaching from below (i.e. for gels with 0.29< C/S < 0.8), as well as from above, as reported elsewhere. In addition, a spreadsheet model has been developed to calculate the volume of backfill required at the vault scale to meet specified pH performance criteria. This model includes the major reactions of the backfill with thegroundwater, waste encapsulants and waste components. It can also consider the effects of specific waste packages on local pH performance to allow comparison with the vault-scale calculations.

Keywords

evolutionnear-field performancebackfillengineered barriercalcium silicate hydrateC-S-H gelsdisposal concept
Type
Research Article
Information
Mineralogical Magazine , Volume 76 , Issue 8 , December 2012 , pp. 3045 - 3053
Creative Commons
Creative Common License - CCCreative Common License - BY
© [2012] The Mineralogical Society of Great Britain and Ireland. This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY) licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2012

References

Chambers, A.V., Heath, T.G., Hunter, F.M.I. and Manning, M.C. (2003) The Effect of Sodium Chloride on the Dissolution of Calcium Silicate Hydrate Gels. Serco Assurance Report, SA/ENV- 0623.†Google Scholar
Chen, J.J., Thomas, J.J., Taylor, H.F.W. and Jennings, H.M. (2004) Solubility and structure of calcium silicate hydrate. Cement Concrete Research, 34, 1499–1519.CrossRefGoogle Scholar
Greenberg, S.A. and Chang, T.N. (1965) Investigation of the colloidal hydrated calcium silicates. II. Solubility relationships in the calcium oxide–silica– water system at 25ºC. Journal of Physical Chemistry, 69, 182–188.CrossRefGoogle Scholar
Harris, A.W., Manning, M.C., Tearle, W.M. and Tweed, C.J. (2002) Testing of models for the dissolution of cements - leaching of synthetic C-S-H gels. Cement and Concrete Research, 32, 731–746.CrossRefGoogle Scholar
Heath, T.G. and Hunter, F.M.I. (2011) Calculation of near-field pH buffering: Effect of polymer encapsulant. Serco Assurance Report, SA/ENV-0909.Google Scholar
Heath, T.G., Hunter, F.M.I., Magalhaes, S. and Smith, V. (2011) Spreadsheet model for the impact of waste packages on local pH conditioning. Serco Report, SERCO/TAS/E000356/01, Issue 1. †Google Scholar
Hoch, A., Glasser, F., Baston, G.M.N. and Smith, V. (2009) Modelling pH evolution in the near field of a cementitious repository. TOUGH Symposium, Lawrence Berkeley National Laboratory, Berkeley, California, 14–16.September 2009.Google Scholar
Hoch, A.R., Baston, G.M.N., Glasser, F.P., Hunter, F.M.I. and Smith, V. (2012) Modelling evolution in the near field of a cementitious repository. Mineralogical Magazine, 76, 3055–3069.CrossRefGoogle Scholar
Kulik, D.A. and Kersten, M. (2001) Aqueous solubility diagrams for cementitious waste stabilisation systems: II. End-member stoichiometries of ideal calcium silicate hydrate solid solutions. Journal of the American Ceramic Society, 84, 3017–3026.CrossRefGoogle Scholar
Nirex (1997) Development of the Nirex Reference Vault Backfill: Report on Current Status in 1994. Nirex Science Report, S/97/014. †Google Scholar
Nuclear Decommissioning Authority (2010a) Geological Disposal: Generic Post-closure Safety Assessment. Nuclear Decommissioning Authority Report, NDA/RWMD/030. .Google Scholar
Nuclear Decommissioning Authority (2010b) Geological Disposal. Near-field Evolution Status Report. Nuclear Decommissioning Authority Report, NDA/RWMD/033. .Google Scholar
Nuclear Decommissioning Authority (2011) Geological Disposal: An Introduction to the Derived Inventory. Nuclear Decommissioning Authority Report, NDA/ RWMD/065. .Google Scholar
Swanton, S.W., Fairbrother, H.J. and Turner, N.A. (2004) The Effect of Sodium Chloride on the Dissolution of Calcium Silicate Hydrate Gels. II. Effects of Temperature and Cation Type. Serco Assurance Report, SA/ENV-0725. †Google Scholar
Wang, L., Martens, E., Jacques, D., De Canniére, P., Berry, J.A. and Mallants, D. (2009) Review of sorption values for the cementitious near field of a near surface radioactive waste disposal facility, project near surface disposal of category A waste at Dessel. ONDRAF/NIRAS Report, 5–03.03, version 1. †Google Scholar