Alteration of MX-80 bentonite backfill material by high-pH cementitious fluids under lithostatic conditions – an experimental approach using core infiltration techniques

Dolder, Florian Dominik; Mäder, Urs; Jenni, Andreas; Münch, B. (2016). Alteration of MX-80 bentonite backfill material by high-pH cementitious fluids under lithostatic conditions – an experimental approach using core infiltration techniques. Geological Society Special Publications, 443(1), pp. 281-305. Geological Society 10.1144/sp443.10

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We characterize and quantify processes at a cement–bentonite interface spatially and temporally during a long-term core infiltration experiment.A young ordinary Portland cement pore fluid (K+–Na+–OH−: pH 13.4) was infiltrated into a MX-80 bentonite core with an initial saturated density of 1920 kg m−3 that shifted to 1890–1930 kg m−3 after 761 days. A hydrostatic external pressure of 4.1 MPa and an infiltration pressure of 2.1 MPa were applied in a triaxial-type apparatus. A decrease in hydraulic conductivity from approximately 2.2×10−13 to approximately 4.2×10−15 m s−1 was observed passing from advection-dominated flow to a diffusion-dominated regime. Sulphate replaced chloride in the outflow during the high-pH infiltration period controlled by the dissolution of gypsum, the uptake of K+ by ion exchange, and complex mineral reactions occurred near the inlet. X-ray computed tomography (CT) scans performed repeatedly during the experiment tracked a progressing hemispherical reaction plume in the first millimetres of the bentonite, revealing a zone of bulk density increase. This zone consisted of two distinct, but overlapping, zones of Mg- and Ca-enrichment related to precipitation of saponite and calcite. The experiment attested an effective chemical buffering capacity for bentonite, a progressing coupled hydraulic–chemical sealing process and also the preservation of the physical integrity of the interface region in this set-up with a total pressure boundary condition on the core sample.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geological Sciences
08 Faculty of Science > Institute of Geological Sciences > Rock-Water Interaction

UniBE Contributor:

Dolder, Florian Dominik; Mäder, Urs and Jenni, Andreas

Subjects:

500 Science > 550 Earth sciences & geology

ISSN:

0305-8719

Publisher:

Geological Society

Language:

English

Submitter:

Andreas Jenni

Date Deposited:

07 Jun 2017 13:14

Last Modified:

07 Jun 2017 13:14

Publisher DOI:

10.1144/sp443.10

URI:

https://boris.unibe.ch/id/eprint/96088

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