Reactive Transport Simulation of Low-pH Cement Interacting with Opalinus Clay Using a Dual Porosity Electrostatic Model

Jenni, Andreas; Mäder, Urs (2021). Reactive Transport Simulation of Low-pH Cement Interacting with Opalinus Clay Using a Dual Porosity Electrostatic Model. Minerals, 11(7), p. 664. MDPI 10.3390/min11070664

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Strong chemical gradients between clay and concrete porewater lead to diffusive transport across the interface and subsequent mineral reactions in both materials. These reactions may influence clay properties such as swelling behaviour, permeability or radionuclide retention, which are relevant for the safety of a radioactive waste repository. Different cement types lead to different interactions with Opalinus Clay (OPA), which must be understood to choose the most suitable material. The consideration of anion-depleted porosity due to electrostatic repulsion in clay modelling substantially influences overall diffusive transport and pore clogging at interfaces. The identical dual porosity model approach previously used to predict interaction between Portland cement and OPA is now applied to low-alkali cement—OPA interaction. The predictions are compared with corresponding samples from the cement-clay interaction (CI) experiment in the Mont Terri underground rock laboratory (Switzerland). Predicted decalcification of the cement at the interface (depletion of C–S–H and absence of ettringite within 1 mm from the interface), the Mg enrichment in clay and cement close to the interface (neoformation of up to 17 vol% Mg hydroxides in concrete, and up to 6 vol% in OPA within 0.6 mm at the interface), and the slightly increased S content in the cement 3–4 mm away from the interface qualitatively match the sample characterisation. Simulations of Portland cement—OPA interaction indicate a weaker chemical disturbance over a larger distance compared with low-pH cement—OPA. In the latter case, local changes in porosity are stronger and lead to predicted pore clogging.

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

UniBE Contributor:

Jenni, Andreas and Mäder, Urs

Subjects:

500 Science > 550 Earth sciences & geology

ISSN:

2075-163X

Publisher:

MDPI

Language:

English

Submitter:

Andreas Jenni

Date Deposited:

08 Jul 2021 17:19

Last Modified:

29 Apr 2022 16:37

Publisher DOI:

10.3390/min11070664

Uncontrolled Keywords:

cement—clay interaction; diffusion; dual porosity; electrostatic effects; reactive transport modelling; near field; radioactive waste repository; low-pH cement

BORIS DOI:

10.48350/157413

URI:

https://boris.unibe.ch/id/eprint/157413

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