Effect of a cement-bentonite grout on AVM glass alteration and C-steel corrosion at nanometer scale

Two experimental mockups were operated for one year at 70°C to study the corrosion of C-steel and alteration of AVM glass surrounded by Cox claystone. Only one system included cement-bentonite grout (CBG). Nanometer-scale analyses (TEM, XANES) examined the glass/C-steel interface to assess CBG's effects. The most notable difference was the presence of a nanometric magnetite layer on the C-steel surface in the CBG system. This layer, promoted by the slightly alkaline pH (8–10) solution influenced by CBG, could act as a passivating barrier, potentially mitigating corrosion, although corrosion rates showed no significant differences over one year. A 5 µm-thick sodium-depleted gel layer of disordered SiO ₂ formed on AVM glass in both systems, with similar porosity (14–20 nm). The open porosity may limit the gel's protective capacity. However, glass alteration rates decreased over time due to passivation mechanism primarily driven by reduced diffusion through the gel layer, with chemical affinity playing a lesser role. Secondary phases (Si-Fe-O, Si-Mg-O) were detected only in the CBG system, likely originating from the claystone or CBG rather than the glass itself. These findings indicate that CBG had little effect on AVM glass alteration but may enhance long-term C-steel corrosion resistance through magnetite layer formation.