15 years of in situ cement–argillite interaction from Tournemire URL: Characterisation of the multi-scale spatial heterogeneities of pore space evolution

• Published in: Applied geochemistry Vol. 26; no. 12; pp. 2159 - 2171
• Main Authors: Gaboreau, S., Prêt, D., Tinseau, E., Claret, F., Pellegrini, D., Stammose, D.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-12-2011; Elsevier
• Subjects: Analogue; Autoradiography; bentonite; cement; Cements; clay; data collection; Earth Sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental Sciences; Evolution; Exact sciences and technology; Geochemistry; Global Changes; Heterogeneity; Materials selection; Mathematical models; mechanical properties; Pollution, environment geology; Porosity; radioactive waste; safety assessment; Sciences of the Universe; solutes; steel; France; Europe; Aveyron France; Western Europe; argillite; fissures; steel; extension; bentonite; protection; networks; radioactive waste; spatial distribution; clay; solution; safety; cement materials; clastic rocks; models; interfaces; autoradiography; porosity; clogging; host rocks; bridges; biosphere; heterogeneity; in situ; sedimentary rocks; cement; materials
• ISSN: 0883-2927; 1872-9134
• DOI: 10.1016/j.apgeochem.2011.07.013

► We characterise the porosity of an
in situ cement–argillite interaction. ► Multi-scale characterisation of the pore space is proposed with classic and innovative techniques. ► Porosity measurements was done in both cement and clay materials. ► These sets of data are unique.
The solution selected by some countries to isolate radioactive wastes from the biosphere for up to one million years in deep geological repositories includes a multi-barrier disposal design, with steel canister, bentonite and cement materials. The geochemical contrast between such materials and the host rock formation creates perturbations potentially altering the confinement properties of the formation. In this context, the French Institute for the Radiological protection and Nuclear Safety (IRSN) have developed an
in situ experimental programme based on the study of cement/argillaceous formation interfaces in their Underground Research Laboratory at Tournemire (Aveyron, France). An
in situ engineered analogue of a cement/clay-rock interface which has undergone 15
years of interaction has been characterised. Such important interaction time for an
in situ engineered analogue provides a bridge between laboratory-derived data and the long time scale of safety assessment modelling. As the mineralogical and petrological investigations have already been published, this work presents for the first time a quantitative characterisation of the spatial distribution of the porosity in the cement and the clay-rock in terms of time scale and design. Interfaces have been characterised using an autoradiography technique in addition to petrophysical measurements. This technique enables visualisation and quantification of the spatial distribution of the porosity using 2D mapping of decimetric-scale specimens. Thus autoradiographs allow highlighting the relationship between the field heterogeneities and the pore space evolution in each material in contact. Moreover, the porosity measurements show a clogging of the porosity in the clay-rock while the porosity increases in the cement. The extension of the porosity evolution extends to a centimetre on both sides of the interface but is heterogeneously distributed in space as a function of the fissure network and interface geometries. The connected fissure network visualised using autoradiography in the clogged area could permit solute (e.g. radionuclide) transport and may also be interpreted as an evolution of the mechanical properties of the clay-rock formation upon alkaline perturbation. This set of data, with the spatial quantification of the porosity in both cement and clay materials will be useful to constrain reactive transport modelling and thus to predict long term evolution of an engineered barrier.