In situ interaction between different concretes and Opalinus Clay

Abstract Interactions between cementitious materials and claystone are driven by chemical gradients in pore water and might lead to mineralogical modifications in both materials. In the context of a radioactive waste repository, this alteration might influence safety-relevant clay properties like swelling pressure, permeability, or specific retention. In this study, interfaces of Opalinus Clay, a potential host-rock in Switzerland, and three concrete formulations emplaced in the Cement–Clay Interaction (CI) Experiment at the Mont Terri Underground Laboratory (St. Ursanne, Switzerland) were analysed after 2.2 years of interaction. Sampling techniques with interface stabilisation followed by inclined intersection drilling were developed. Element distribution maps of the concrete–clay interfaces show complex zonations like sulphur enrichment, zones depleted in Ca but enriched in Mg, strong Mg enrichment adjacent to the interface, or carbonation. Consistently, the carbonated zone shows a reduced porosity. Properties of the complex zonation strongly depend on cement properties like water content and pH (ordinary Portland cement vs. low-pH cement). An increased Ca or Mg content in the first 100 μm next to the interface is observed in Opalinus Clay. The cation occupancy of clay exchanger phases next to the ordinary Portland cement interface is depleted in Mg, but enriched in Na, whereas porosity shows no changes at all. The current data suggests migration of CO 2 / HCO 3 - , SO 4 2 - , and Mg species from clay into cement. pH decrease in the cement next to the interface leads to instability of ettringite, and the sulphate liberated diffuses towards higher pH regions (away from the interface), where additional ettringite can form.

[1]  D. Bartier,et al.  Mineralogical characterization of the Tournemire argillite after in situ interaction with concretes. , 2006, Waste management.

[2]  D. Newbury,et al.  An electron microprobe study of a mature cement paste , 1984 .

[3]  F. Glasser,et al.  Mineralogical and microstructural changes accompanying the interaction of Boom Clay with ordinary Portland cement , 2001 .

[4]  Alexandre Dauzères Etude expérimentale et modélisation des mécanismes physico-chimiques des interactions béton-argile dans le contexte du stockage géologique des déchets radioactifs , 2010 .

[5]  B. Lothenbach,et al.  Thermodynamic modelling of the hydration of Portland cement , 2006 .

[6]  F. P. Glasser,et al.  The magnesia–silica gel phase in slag cements: alkali (K, Cs) sorption potential of synthetic gels , 2005 .

[7]  B. Lothenbach,et al.  A thermodynamic approach to the hydration of sulphate-resisting Portland cement. , 2006, Waste management.

[8]  G. Kosakowski,et al.  The evolution of clay rock/cement interfaces in a cementitious repository for low- and intermediate level radioactive waste , 2013 .

[9]  Eric C. Gaucher,et al.  In-situ interaction of cement paste and shotcrete with claystones in a deep disposal context , 2012, American Journal of Science.

[10]  Barbara Lothenbach,et al.  Hydration of a low-alkali CEM III/B–SiO2 cement (LAC) , 2012 .

[11]  D. Grolimund,et al.  X-ray micro-diffraction studies of heterogeneous interfaces between cementitious materials and geological formations , 2014 .

[12]  Christophe Tournassat,et al.  Influence of reaction kinetics and mesh refinement on the numerical modelling of concrete/clay interactions , 2009 .

[13]  M. Cathelineau,et al.  A reinvestigation of smectite illitization in experimental hydrothermal conditions: Results from X-ray diffraction and transmission electron microscopy , 2011 .

[14]  C. C. Coumes,et al.  Physico-chemical investigation of clayey/cement-based materials interaction in the context of geological waste disposal: Experimental approach and results , 2010 .

[15]  A. Meunier,et al.  A new method for quantitative petrography based on image processing of chemical element maps: Part II. Semi-quantitative porosity maps superimposed on mineral maps , 2010 .

[16]  Alain Meunier,et al.  An Imaging Method for the Porosity of Sedimentary Rocks: Adjustment of the PMMA Method--Example of a Characterization of a Calcareous Shale , 2002 .

[17]  D. Pellegrini,et al.  15 years of in situ cement–argillite interaction from Tournemire URL: Characterisation of the multi-scale spatial heterogeneities of pore space evolution , 2011 .

[18]  A. Lindberg,et al.  Study of porosity and migration pathways in crystalline rock by impregnation with 14C-polymethylmethacrylate , 1993 .

[19]  K. Kawamura,et al.  Swelling behavior of Na- and Ca-montmorillonite up to 150°C by in situ X-Ray diffraction experiments , 2009 .

[20]  D. Beaufort,et al.  Porosity distribution in a clay gouge by image processing of 14C-PolyMethylMethAcrylate (14C-PMMA) autoradiographs:: Case study of the fault of St. Julien (Basin of Lodève, France) , 2004 .

[21]  T. Sterckeman,et al.  A comparison between three methods for the determination of cation exchange capacity and exchangeable cations in soils , 1997 .

[22]  M. Bradbury,et al.  A Physicochemical Characterisation and Geochemical Modelling Approach for Determining Porewater Chemistries in Argillaceous Rocks , 1998 .

[23]  I. Sims,et al.  Concrete Petrography: A Handbook of Investigative Techniques , 1998 .

[24]  D. Rentsch,et al.  Hydration of a silica fume blended low-alkali shotcrete cement , 2014 .

[25]  L. D. Windt,et al.  Reactive transport modeling of geochemical interactions at a concrete/argillite interface, Tournemire site (France) , 2008 .

[26]  C. Gallé,et al.  Effect of drying on cement-based materials pore structure as identified by mercury intrusion porosimetry: A comparative study between oven-, vacuum-, and freeze-drying , 2001 .