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

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