International audience The reactivity of well materials, individually considered in the case of geological storage of CO2, is well documented. However, a lack of data concerning the reactivity of the interfaces between these materials still remains. This observation led the G2R laboratory (Université de Lorraine) to develop an original experimental set-up called "Sandwich". It consists in performing CO2-ageing of composite materials. The reactivity of a caprock/cement interface was thus examined after 30 days of exposure to CO2 at a temperature of 80°C and a pressure of 100 bar. A SEM study showed a fracturing of the interface, which was partially filled with carbonate minerals. The comparison with the blank samples aged in the presence of N2 leads to the conclusion that the CO2 is responsible for the fracturing, due to the precipitation of carbonates and the induced crystallization pressure.