Many deep disposal concepts for radioactive wastes in natural clay formation use cementitious materials as structural support material for access galleries and disposal drifts of cells (e.g. concrete/shotcrete), backfill and waste matrix. Thus, cementitious materials can be in contact with clay host rock. Due to contrasting chemical properties between cementitious materials and clays, chemical gradients occur at concrete-clay interface involving chemical and miner alogical perturbations. Nevertheless, long-term in situ mineralogical evolution remains poorly documented in the literature. In 2009, five experiments were placed between -5m and -7m below the concrete invert of the main drifts of Andra's underground research laboratory to be dismantled at five deadlines (1- 2, 5, 13 years). For each experiment, a 101 mm-diameter borehole was drilled in the Callovian Oxfordian clay rock (COx). Three concrete formulations (CEM I, CEM V and low pH) were poured, separated by bentonite/sand compacted interlayers (Figure 1a). The interlayers were saturated with synthetic pore water between each concrete emplacement. In 2021, 12 years after the beginning of the experiment an overcoring was carried out on one of the borehole to characterize the concrete/Cox interfaces. A multi-technical approach including micro X-ray fluorescence, X-ray diffraction (XRD), SEM observations and electron microprobe mapping was used to investigate mineralogical and chemical changes in clay host rock and concrete materials. Additional cation exchange capac ity, anion leaching, strontium isotopes on the clay exchanger, and (C, O, Sr) isotopes on calcite were conducted on the clay host rock at different distances from the interface, to further inves tigate chemical changes of clay and calcite fraction in the clay host rock