Interaction processes at the concrete-bentonite interface after 13 years of FEBEX-Plug operation. Part II: Bentonite contact

Authigenic Clay Minerals from Interface Reactions of Concrete-Clay Engineered Barriers: A New Perspective on Mg-Clays Formation in Alkaline Environments

“…The formation of a Mg enriched zone within the concrete-clay interface, characterized by the formation of Mg-silicates hydrates (M-S-H), is known as Mg-perturbation. It has been recognized elsewhere when clay rocks or compacted bentonite are held in contact with solid cementitious materials [8,[10][11][12][13][14]. Usually, the source of Mg comes from the bentonite exchange complex or through the dissolution of Mg minerals in the concrete (i.e., brucite) or in the clay rocks (dolomite, serpentine, chlorite).…”

Investigating the Potential Barrier Function of Nanostructured Materials Formed in Engineered Barrier Systems (EBS) Designed for Nuclear Waste Isolation

“…To advance this characterization, we applied thermal, infrared and Si and Al NMR methods. The thermal analysis confirms the presence of brucite‐like and disordered MSH‐like phases with broad dehydroxylation effects between 450 and 550 °C that are not produced in the bentonite outside the altered rim ,. The broad 550–650 °C dehydroxylation of Mnt in these samples and the presence of calcite also make it difficult to discard the presence of other Mg hydrated silicates with very similar effects to those of serpentine.…”

“…In the present paper, the results from three experimental setups were considered. The experiments exhibit conditions with different complexities, including reaction mixtures in batch reactors,, long‐term concrete‐bentonite column experiments (10 years),, and results from the concrete‐bentonite in situ FEBEX experiment (13‐year‐old interface) ,. Three testing scenarios composed the framework of the research.…”

“…The profiles depicted for the variations in the weight percent of the major elements show a relevant increase in Mg from 1 mm in the concrete side to 2.5 mm in the bentonite side. With an average variation of ±0.5 and ±2 mm in the concrete and bentonite, respectively, the rim has been measured and studied in at least three HB cells (4.5, 6 and 10 years), four interfaces in the FEBEX in situ experiment, two portlandite/bentonite interfaces in small cells (5‐mm‐thick lime mortar and 2‐cm‐thick compacted bentonite), and at 60–90 °C in the alkaline alteration (K, Na−OH, pH=13.5 solution) of a 2‐cm‐thick Mg‐saturated, compacted FEBEX bentonite . Calcite precipitates in concrete when the Mg‐enrichment peak ends after a millimetric rim, and a Ca,Si (Al)‐rich region develops as the Mg decreases (i. e., a calcium aluminum silicate hydrate phase (C−A−S−H)).…”

“… Composition of the chemical analysis and mineralogical zonation (major cations Ca, Si, Al and Mg, excluding C and O and recalculated to 100 % (Na, K, Fe, and S not shown)) determined by SEM‐EDX showing the characteristic changes in the concrete‐FEBEX bentonite interface. Data elaborated from . 0 on the x scale is the contact interface.…”