Abstract
AbstractConcrete and bentonite are being considered as engineered barriers for the deep geological disposal of high-level radioactive waste in argillaceous rocks. Three hydrothermal laboratory experiments of different scalable complexity were performed to improve our knowledge of the formation of calcium aluminate silicate hydrates (C-A-S-H) at the interface between the two materials: concretebentonite transport columns, lime mortar-bentonite transport columns and a portlandite- (bentonite and montmorillonite) batch experiment. Precipitation of C-A-S-H was observed in all experiments. Acicular and fibrous morphologies with certain laminar characteristics were observed which had smaller Ca/Si and larger Al/Si ratios with increasing temperature and lack of accessory minerals. The compositional fields of these C-A-S-H phases formed in the experiments are consistent with Al/(Si+Al) ratios of 0.2– 0.3 described in the literature. The most representative calcium silicate hydrate (C-S-H) phase from the montmorillonite–cement interface is Al-tobermorite. Structural analyses revealed a potential intercalation or association of montmorillonite and C-A-S-H phases at the pore scale.
Highlights
ABSTR AC T : Concrete and bentonite are being considered as engineered barriers for the deep geological disposal of high-level radioactive waste in argillaceous rocks
The calcium silicate hydrate (C-S-H)-type phases formed in experiments from cement–bentonite interaction have complex chemical composition, mainly due to the intimate mixture with existing clay minerals
When the experimental conditions reproduce more realistic scenarios of interactions between the concrete and bentonite barriers of a radioactive waste repository, the characterization of crystalline disordered C-S-H phases formed at low temperature (
Summary
The medium cells comprise a series of laboratory column experiments performed under the NF-PRO and TABLE 1. The results extracted in the present study were taken from cells HB4 and HB5, performed for 4.5 and 6.5 y, respectively. Both cells included a cylindrical concrete block 70 mm in diameter and 30 mm tall in direct contact with a compacted FEBEX bentonite column 70 mm in diameter and 71.5 mm tall. The cells were heated at 100°C from the bottom (bentonite side) and hydrated from the top (concrete side), simultaneously. These conditions simulate the heat emitted by the radioactive waste from the canister side and the hydration to the engineered barriers system from the host-clay formation side. Detailed descriptions of these experiments and the results obtained for cells HB1–HB4 have been published by Torres et al (2009) and Cuevas et al (2012)
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