In situ interaction between different concretes and Opalinus Clay

Abstract

International audienceInteractions 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 lm 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 CO2=HCO 3 , SO2 4 , 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

5-year chemico-physical evolution of concrete–claystone interfaces, Mont Terri rock laboratory (Switzerland)

“…Compared to OPC, the ESDRED cement matrix contains up to twice the proportion of Si in all zones due to the addition of silica fume. Jenni et al (2014) C6: less portlandite and Mg-hydrate; some relict belite; close to bulk unreacted cement.…”

5-year chemico-physical evolution of concrete–claystone interfaces, Mont Terri rock laboratory (Switzerland)

“…This reinforced section was overcored with a single-barrel 86 mm outer diameter (OD) diamond drilling tool equipped with a core catcher and using a simple Hilti drilling machine and compressed air as cooling agent. This operation was only partially successful, and provided only a limited amount of intact LAC and OPC interface samples (Jenni et al 2014). The interface between ESDRED and Opalinus Clay was recovered from a mock-up experiment of identical age and material and using the same coring technique (Fig.…”

“…This may lead to mineralogical alteration in the barrier system which in turn is expected to locally influence properties like porosity/permeability, swelling pressure or specific retention properties in case of concrete in contact with claystone or compacted bentonite. Laboratory experiments (Adler 2001;Adler et al 2001;Dauzeres et al 2010) and in situ experiments (Read et al 2001;Tinseau et al 2006;Gaboreau et al 2011Gaboreau et al , 2012Techer et al 2012;Jenni et al 2014) demonstrate alteration of both cement paste and claystone adjacent to interfaces. An increase in porosity in the cement paste close to the interface, and clogging in the claystone adjacent to it are commonly predicted by reactive transport modelling (De Windt et al 2008;Marty et al 2009;Kosakowski and Berner 2013;Bradbury et al 2014).…”

Impact of a 70 °C temperature on an ordinary Portland cement paste/claystone interface: An in situ experiment

“…1). Katoite is part of a solid series between two endmembers, grossular (Ca 3 Al 2 Si 3 O 12 ) and synthetic phase (Ca 3 Al 2 (OH) 12 ), also known as hydrogarnet. In this paper, the term katoite is used for Si-katoite (C 3 ASH 4 ).…”

“…Only a handful of studies have discussed the interactions at the interface between cement binder and claystone. Such interfaces have been created at ambient temperature by pouring cement mixes into boreholes [11][12][13] or by putting disks of material into contact in transport cells [14]. In the current design of the French radioactive waste deep disposal facility [15], the thermal transient, due to the presence of heat-emitting waste, is expected to entail a temperature increase of up to 70°C in the concrete plugs located in the high-level waste cells and potentially also in the intermediate long-lived waste cells.…”